928 Trailer Hitch/Tow bar
 

I have a customer looking to purchase a trailer hitch/tow bar set up for a 928.
If you have one, or know where I can find one please email me at Roger@928srus.com.
Thanks,
Roger:bigbye:

I am looking for one too.. I figure they are like hens teeth :)

they are probably on a pallet next to where Greg B found the stash of transmissions

The best ones are home brewed. I like the one that comes out of the license plate area. A hole is cut in the bumper cover behind the plate, and the plate is on spring swivel. There's a receiver mounted behind the plate to the bumper bar. Tip down the plate, insert the hitch in the receiver and away you go!

You could build one for very little. Here's my solution.

Angle iron from Home Depot: $15
Grade 10.9 nuts and bolts: $5
944 bumper shocks, welded solid: free from parts car
Tow bar: $ varies, but roughly $130

http://sphotos.xx.fbcdn.net/hphotos-...34535351_n.jpg

http://sphotos.xx.fbcdn.net/hphotos-...73988550_n.jpg

I towed the car about 10 miles a couple weekends ago with no issue. I've been towing my 924S to and from the track for over 4 years with a nearly identical setup.

The best part is I can bolt the bumper on and the tow bar arms fit through the fog light holes (since I deleted them).

That's pretty cool, but I think Roger means a rear towbar?

https://members.rennlist.com/porken/Towbar.jpg

D'oh! :banghead:

IF you do manage to get hold of one Roger, the PLEEAAASSSSEEEEE take a full set of measurements so they can be replicated. I am sure you could make and sell a few.

Myles

I could easily make one of these.

But the style I prefer is the style that TerryGT has on his car. It requires the entire bumper cover to be removed and the aluminium bumper be modified. Then the hitch gets put through the rear license plate (on a flip down hinge).

I will look into the costs associated with making this style though as it doesnt require the rear cover to be removed.

What size of ball do y'all want?

Why not mount a standard receiver behind the license plate, and insert a standard hitch (with the desired size ball and amount of lift) only when needed?

Colin /Wally etc,
I would much prefer one that attached to (at least) the factory points and was hidded behind the bumper cover with a removeable std type hitch receiver if this is possible.

With this setup the owner could then choose the ball size.

Myles

928Myles,

For that design, you will require taking off the rear bumper cover, cutting a hole in the cover, and either shipping the rear bumper to me, or me shipping you the pieces ready to have a shop over there weld it on.

But if you do that, then I could not guarantee that their welds are strong enough.....

Nothings ever easy is it.

If I could figure out the stock mounting points then I could probably make something up myself. It would be good to get a photo of one mounted on a car to confirm exactly how they were mounted by the factory.

Something in the back of my mind tells me that the one Wally pictured is not factory - can anyone confirm that?

Myles

IIRR there used to be at least two different setups. Westfalia was what factory sold at the time. Kovil made aftermarket setup which I think used same mounting points as factory. Or it could have been done by some Kovil dealer using generic parts.

I made one based on a design from a long time 928 DE guy in Indiana - Randy Faunce - who I met at Road America. I only pull a small 2 wheel trailer with 4 wheels/tires and a tool box weighing a total of about 500 lbs to and from the tracks.

Piece of flat steel bolts onto the bottom of the aluminum bumper bar, has a receiver welded to it, and a hole cut in the plastic "bumper" behind the license plate. Use a '50's type GM license plate holder that has a hinge and folds down. Slip the receiver with a 1 7/8" ball into it, insert the locking pin and I'm ready to connect the trailer and the electrical wiring for it's lights.

Once I'm at the track, just withdraw the locking pin that is behind the plastic bumper and withdraw the square bar from the receiver and flip the license plate up for the event.

Anyone who wants a copy of the "plans", send me a direct e-mail. I 'think' I can find them in my files somewhere!!

Gary Knox

If you meant the photo that Ken posted - that is the factory hitch. No welding, it just bolts to the mounting points for the bumper shocks and additional points. If I built one, it would bolt on pretty much the same way, but would have a US-standard hitch receiver rather than the flat plate just behind the license plate. Much like Gary's - but I wouldn't hook to the aluminum bar for anything heavier than what Gary is doing.

When one shows up, lets do an auction for it. I'd like one too.

I'll bet there is a market for at least 100. I'd buy one with a 2" hitch receiver. I want to carry less than 200 pounds (total) of bike carrier and bicycles.

I'd buy one for a tire trailer. But then I'd have to find a suitable tire trailer. Hmm.

Got the tire-and-tools trailer, Rob. Yours whenever you need it. Problem for most of us urbanites is how to store the trailer between uses.

Brainstorming hitch options...

The tow-eye in the rear bumper is strong enough to pull the car. A hitch adapter that used those threads in the aluminum bumper beam might be cool for light duty stuff like the tire and tool trailer. Threaded pin to fit the bumper, a lock nut or lock plate of some kind to keep it from loosening in use would be needed. Box receiver on the aft end for standard attachments.

my thoughts as a "racer"....IF you have the rear bumper internals in place....you could easily modify it to a trailer.....remember 928's are rated to pull 1500lbs without trailer brakes and 3500lbs with it....

while I wouldn't pull 3500lbs from a custom tow eye hitch....1500lbs would be easy....a 500lbs single axle trailer with only tires-tools is super easy...

I see TONS of "sports cars" at the track pulling little trailers....Miatas through Corvettes....

For only EUR 3343.00, you can get a whole shark with the trailer hitch already installed...

http://www.ebay.de/itm/Porsche-928-S...#ht_500wt_1156

Like this?

Exactly like that. :cool:

Nick in Oz is also selling his car with a hitch , i asked for the hitch without the car but .....well he wants to sell the car!

Am I the only one who thinks this is a very weird place to mount a hitch? A part that's designed to move, to "give" when hit by forces, and made of deformable aluminum?

Got one!
 

Roger, the 87S4 I bought last year came with a factory hitch. The documentation I have from the PO even has the specs from Germany. I'll scan and post later today. I'll take bids on my hitch! I don't think I'll ever tow anything with my baby. What do they go for? I could use a cash infusion (intake & TB/WP) on the horizon

Nicole,

You are absolutely correct about the "designed to move/bend when hit". However, I have been using that exact hitch - got the plans from Randy Faunce - for 7 years to pull a 4' X 4' trailer with 12" tires that weighs about 450 lbs including 4 Porsche wheels/tires and a tool box full of "stuff" to and from tracks. Furthest track has been ~850 miles each way, closest one is 250 miles each way. Most trips are through parts of the Allegheny mtns. NOT AN ISSUE ever. I did, however, use a much longer steel plate (~18") and 6 bolts that attach it to the bottom of the aluminum channel.

I have the tow eye installed, and a safety chain attached to each side of the trailer in front, as well as the electrical hookup for the turn signals and brake lights.

Rob/Bob, the trailer is one sold by Harbor Freight. They also sell one - or at least used to - that is 8' X 4', and folds in the center, allowing it to be stored easily. Another 928 track guy - Physics professor at a big 10 school - had one of these for his track stuff and his kids bicycles for several years.

Gary---

A reader on this forum named Joe sent me a request for the plans for this tow hitch. I CAN NOT respond to the address that was supplied. Joe - please send me a Private Message.

Gary--

that black GT looks just like the one in my garage ! I have a hitch on both my 928,s . The GT has just a reciver bolted to the alum bumper beam , with a flip down plate holder .Only capable of towing very light trailers . My 81 has a frame mounted hitch that I made and has towed 3500 # + . As a major trailer manufacturer, 50,000 and counting , making and developing a hitch for the 928 would not too hard . I would have to check to make sure our product liability insurance covered it . Anyone else building a hitch should do the same .

Hitch Info
 

Here is some info on the hitch. The one I have is just like the one in Porken's Pic. What are these things worth? I see where the PO paid $207 just for the ball neck. I also have the wiring harness.

On the car
 

Here is the pic on the car

Sorry
 

The pics won't upload:banghead:

If you have the harness and all the mounting hardware, I'll open the bidding at $400 plus actual-cost shipping to the PRK.

Dumb question-

Per PET, it looks like there are 2 flavors of factory tow hitch:

928 722 031 02, for 78-86

928 722 003 00, with wiring harness, for 87-91. 'cept the wiring harness (928 612 905 01) is separately listed for '85 and up.

I wonder what the difference is?

FWIW, I need the hitch for a 78-86 car.

First time I've seen all of the parts for the install.

What does (42) do?
Where does (40) attach?
(55) attaches to the battery box?


http://members.rennlist.org/porken/HitchParts.jpg

I have a factory hitch on my 85. When the draw bar isn't installed it is fairly inconspicuous, not as much so as, the ones with the receiver in front of the license plate, but still fairly concealed. I’ve tried numerous times in the past put have been unable to get any reasonable pictures of the mount points until recently. I had the fuel tank out the other week which allow for me to snap a few pic’s of the installed hitch (cell phone camera so not great). I will try to post them here in in the near future.
To mount the factory hitch the rear bumper cover does have to be removed, as the side mounts attach at the bumper shock mounting points. If you notice on the pic that PorKen posted the side mounts are “C” shaped to reach both the upper and lower mount bolts. With the “C”s both facing the center you cannot get the hitch in place without removing the rear bumper shocks, necessitating the removal of the rear cover. If someone were to replicate the OEM hitch and face both the “C”s in the same direction I believe it would greatly simplify installation. I personally like the factory style hitch mount as it does not rely on the bumper shocks to carry any load. Also the torque applied to the hitch it handles by the long forward arm of the hitch. In a bumper mounted hitch all the tongue weigh and torque of the pulling and stopping force (if the ball isn’t perfectly in line with the center of the bumper shocks) is carried by the bumper shock mounting bolts which are only a couple inches apart. If you are only carrying a very light load this is probably acceptable, but I wouldn’t want to rely on it.
I think the ideal setup would be one which picks up the factory mount poits but incorporated a standard 2” receiver. For mine I currently have the 50mm ball which allows me to tow any trailer with a standard 2” ball hitch. I however also have a trailer with a 1 7/8 hitch, and I would like to have the ability to use hitch mounted bike racks and other standard hitch accessories, but of course none of it interfaces with the factory mount. When time permits I figure I will make an adaptor to go between the OEM hitch and whatever accessory want, just haven’t had time yet.

Intresting hitch drawing Ken . If I had a original hitch , I could copy it and do a run of them , with a 2" reciver style hitch .And some mounting updates.

That would be sweet. I'd be in.

Dan
'91 928GT S/C :eek: 475hp/460lb.ft

+1

Unfortunate that we don't live closer. I would be more than happy to let someone take any measurements and attachment details (though it looks as though I'm missing a couple parts in the sketch above, I don't have 40 or 41) from mine. I'll admit it would be really convenient to have the 2" receiver incorporated.

Parts from drawing above

#51 Vertical link attaches through right rear of spare tire well with bolts #46. (Pic 1 below)

Left and right ends of hitch #19 attach at “C” shaped brackets to bumper shock mounting points with bumper shock mounting bolts #44 and #45. (Pic 2 below)

Forward end of hitch #19 attach through forward side of spare tire well with bolts #44 and #46, and vertically through rear deck with bolt #46, and forward through body with bolt #46. (Pic 3 and 4 below)


I believe #40 is designed to capture as much body material as possible to distribute the load at the forward end of the hitch. I do not have this piece, and didn’t know it existed until the above drawing was posted, so during my install I used oversized fender washers. I also the rearward hole on the forward arm of my hitch was not a through hole it only penetrated one layer of the overlapping welded arm so I did not install a bolt at that location. I also did not see how to gain access to the forward side of the body sheet where the forward facing bolt would be located so I omitted that bolt not knowing how to get a nut on it. Looking at the drawing all locations where #42 interface with bolts there are no nuts present, so I assume #42 are tapped nut plates which may explain how the forward bolt would be installed. I’ll have to go back and look at that area again and see if there is access to install them, if I can still see the area since I have reinstalled my tank.

Awesome. Makes sense, now.


(40) and (41) mount inside the cabin, as backing plates.

yes 41 and 42 are backing plates. they also provied additional fore/aft bolt locations to further distribute the load.

I posted info on where to buy these in Germany many months ago. The company is Oris. They may still be in business.

Simon, also in photo 2 is a large crack, with what appears as some displacement to the "C" bracket. Might be time to remove the hitch for some maintenance.

In the big circle is a shadow. Not sure what's in the small circle.

Attachment 675056

They are:

and I emailed them for a price. I will see what they come back with. The site is all German and I am not that good at reading it yet... http://www.autoteile-shopping24.de/products/3379914/

Thanks for the info... If I can get one for less than a kings ransom, I would be willing to ship it direct to the folks that want to build in the 2" ball...

Emerald

good pictures they show the mounting points . not the greatest lay out or construction , I think a better mount could be built . plasma cut the parts / two piece construction / 2" reciver . Maybe I should build 20 or so . ?

Yes, please do. I'll take one.

I'm in for ~5% of the production run.

I would probably take one too. Depending on price.

+1

Keep us informed about your progress on getting a new Oris hitch. It will be interesting to see if they're still available, and if they are how much they want for one.

Suppose if it comes down to it and there's enough demand to actually implement a redesign, I could be persuaded to pull mine and send it out for reverse engineering.

If it costs way less than $1500 for a factory original one from autoatlanta, then I am really interested in one for my 81.

Yaaa, which model are you referring to the factory-type or the behind the license plate-type?

Out of curiosity I called autoatlanta, both the per and post 86 hitches are NLA. They have them listed on their site but have no availability.

OK, Terry GT, we need you to gin up a bunch. I want a behind the license plate 2" receptical capable of supporting a bike rack and 4 bicycles. GW about 200# with some bounce.

Anything more on this project? I'd sure be in for something. I'm seeing a setup like this in my mind, for the 928. Maybe put a big wing on the back of the trailer to match the car :)

http://www.sportscarillustrated.com/.../C/12_0233.jpg

I am off to Maui for a bit, then I will get the hitch project underway. First thing I need is a dead car so I can fit it up , and later rip the hitch out to test it .

Enjoy your trip. I'd like a hitch before the Minnesota cycling season starts in May, 2013.

Guys...I have an '81 euro with the factory hitch. I'd sell it considering I have no interest in trailering anything. It's clean and actually very cool looking. It tucks up under nicely also. I am a bit concerned about what removing it will do to the value of my car....my car also came with a factory telephone.

Car would make a good trailer

Only if you tow it backwards....

don't know

I am interested. Need to pull a motorcycle trailer.

That had crossed my mind as well. I think the complication would be that the rear axle would be way to far back and you would end up with a lot of excess tongue weight (which the 928 can't handle). So to do it you would need to relocate the axle further forward. It would probably make more sense to remove all the original rear suspension anyway so you could drop the floor to increase the interior room. Also I thought it would be ideal to have a canvas enclosure to allow the rear hatch to be popped when in use as a camper.

Also you can disregard the function of the W. axle when used as a trainer. The axle needs fore and aft thrust at the wheels to function, and a free rolling trainer will not do this.

my trailer hitch
 

Not the best pics but they give an idea. All original untouched. Still has the factory paint. Not sure what the value would be. Open for offers or may list on ebay. I have no use for it. Attachment 709028

Attachment 709029

Attachment 709030

Do you have the ball to go with it? If so do you know what size it is? Mine has the 50mm ball which works with standard 2" trailers. Don't know what options where originally available, but would like a ball that works with 1 7/8" hitches too.

I don't have the ball. Sorry.

Simon-is your hitch like mine?

agreed

Yes, it is identical to yours.

I would love to do it, but have so many things that would take priority; I doubt I’ll ever get around to it. Not sure how one would add air support to the rear of a 928, with the coil overs on the rear. I’ve seen bags that go inside coil springs and I've seen air shocks, but neither of these would be directly adaptable to the rear of a 928. Cutting it off I front of the hatch hinge seems pretty messy to me. If it were to be done it seems to me the logical thing to do would be to cut it at the firewall. The tongue section could then attach were the front frame rails currently are and then to finish off the trailer all you would need to do would be build a fairing to conceal the firewall. the tub would already be sealed as it currently is, with the exceptioin of havine to address a few areas where electrical and hoses pass through the tub.

me too

Sharkfest Beer Caddy
 

beer, other where fuel tank was

That doesn't look too bad. I'm just thinking if I'm going to be dragging an enclosed trailer around, might as well be long enough to sleep in.

would be a lot of fun, will do when i retire.

Just to resurrect this thread. Has anyone scored an original or templates for a light duty hitch?

Could be made easily

plenty of 928 material to work w/ back there/ attach hitch to.

Emerald...did you ever get a response from Oris about the hitch?

post#48 https://rennlist.com/forums/9951391-post48.html

I'd be interested.
Joe
6120865-7956

@F4GIB I too would be interested in a bike rack out of a 2inch reciever. but what confuses me is if the reciever is behind a flappy license plate then how is the plate visible when you are towing something?
you could make a shark train with a a few of these lol.. weight permitting... if you get brakes in the trailers you could probably get two or three lol. also you can get aerosol waterproof stuff that you spray on ageing raincoats to re waterproof them

The bike rack loaded with bikes obscures the plate on my Jeep. In 4 years, no cop has noticed. Not a significant risk.

...and I have the car! Gary, I'll check the paperwork you provided me,but I don't think you have that to me. However, I can take pics of the setup AND you can see it live of you go to Frenzy (without the actual trailer). It's so simple, yet so brilliant.

I did not. Sorry for the slow response. I gave up. I still would love to have this setup for my 89 with the hidden connection under the plate.

E

Still working on a trailer hitch . Its not as easy as one would think . The hitch on my GT is simply a plate welded to a 1 1/4 " reciver tube and bolted under the alum bumper ,a hole cut in the bumper ,with a flip down LP holded . It is VERY VERY light duty , a bike rack is out of the question . My 81 has a much stronger set up , but is visable . What I am working on is a high cap ,hidden hitch that dose not require the removal of the bumper cover to install like the factory one did . So you can use a bike rack and tow something like a class 1 hitch .

Ill take 1 for sure. Let me know if you need seed money.

Thanks for the offer . Money is not one of my problems , time is .

I have the Original ORIS D83 hitch on my 86. Im looking for a ''ball'' for it... Any pointers?

Factory Hitch FSS
 

I have the original hitch with the ball and some sort of wiring harness I'll take $550 + shipping for. Price is because I have to pay someone to remove it. I'm not able to health wise right now. I posted the info on the Oris Hitch. It's the same one. PM me if interested.

You might want to start your own thread as many do not look this deep into the thread.

I am interested, but funding is allocated elsewhere right now.

PM sent

Terry GT

Have you had time to work up the trailer hitch yet?

Update
 

Update: I got a reply from ORIS / Bosal. Unfortunately no longer available from them, meaning the OEM:

No, its on my "list" but I am over my head in work and personal issues . Sorry

Did any of these tow bar re-creation projects ever come to?

if I could get a factory hitch to use as a starting point , it would push me along . then adapt it to a receiver style hitch ,std 2" . would also be nice not to have to re and re the rear bumper set up . then some testing to confirm its load capacity .

U-Haul will make one for free if you can get your car to their Tempe, Az location.
I need one, but that too far and snakey for me.

I'm pretty sure I don't want to have the U-Haul guys trying to fabricate one on the car. The mounting access for the rear supports would require welding up "inside" the PU bumper cover after sandwiching steel plate between the bumper shocks and the rear bumper beam/crossbar. Then getting that forward brace tied to the aluminum suspension crossmember will add to the challenge, welding under the fuel tank. I think that whoever takes on this task will end up with a fixture to locate the mountings correctly, so all the welding is done with full access.

To me this is a task assignment most appropriate to a Ken or Jake (Ducman...) or others with the fab and welding skills. Lots of "looks easy" stuff like this is not really that easy. Might be the reason we haven't seen any good aftermarket or DIY options yet.

I don't see why welding on the car would be required. From what I've read the factory bar doesn't require it. Might need to tack the parts together in place, but there are adhesives that can be used for that.
At any rate it's just something I came across during my search. I'm not advocating one way or the other.
On the other hand this thread is six years old and I still don't see any offered for sale.

Edit: Clearly what U-Haul really wants is to make a jig to add to their inventory. I'm sure if someone sent them an original they would be able to use that.

Really...nobody is gonna do this, because liability.

Now Uhaul doing it..well, that would be interesting, and I doubt they would take it on, the OEM setup was IMHO really underwhelming in its design, and im not sure how it could be done better.

https://www.uhaul.com/Trailer-Hitche...eId=10154&ship

It seems they actually have one for an '86. Aren't they all the same? I didn't bother searching further before.

Trying to visualize what that had to be drilled out and bolted to..

It clearly says the picture is not the actual unit.

The hitch was the same 78-95. So that U haul one would work on all 928s.

That is, if they actually manufactured it to fit correctly.

For a buck seventy five I might have to find out. How much was the original?

Did u ever try the u haul hitch?

How fun would it be to drag one of these around with a suspiciously polished silver 928...

https://cimg0.ibsrv.net/gimg/rennlis...ba9e63e914.png

Or... this...

https://cimg3.ibsrv.net/gimg/rennlis...ee3ff09f02.png

What about removing the rear 5 mph shock absorbers and aluminum protection bar under the bumper cover and installing a 3" square steel tube with a receiver welded in the middle behind the flip down license plate?

From what I see you could actually get in there to install and remove it without taking off the bumper cover (after the initial fabrication and instillation adventure).

>

But why?

https://cimg8.ibsrv.net/gimg/rennlis...5b034ac6a.jpeg

Should be done this week, powder coated..and on the car hopefully next weekend, time allowing.

There are a few significant issues with the pictured one thats been around. No gusseting at the mount, and there's even a crack in the photos floating around where it failed.

Going to move the receiver plate back another 1/8" to more comfortably clear the bumper lip you see there, But..we ended up smack on where we expected to from using a chunk of a car I cut up earlier this year, with the strips of aluminum marking where in space the lower bumper lip center and location was from the chassis. We cleared the bumper straps (92850527902) and the muffler hangar may require a teeny weeny adjustment.

Just got tired of years of talking...and decided Yesterday AM to do it. Two 12-6pm days invested so far.

https://cimg3.ibsrv.net/gimg/rennlis...b99a6cce56.jpg

Sweeeeeeeet...

Speedtoys,
Looks like you're off to a good start. I'm excited to see how this turns out, and what the final assembly and tie-in points are.
As for the crack you mention, Are you referring to the pics I posted earlier in this thread? If so, I can guarantee those are shadows and not cracks. Where do you believe that the original is missing/needs gusseting? I agree there are some things that I would change from the original design, but overall I think the original hitch as a very robust system.

Since my 85 (with the hitch installed) got T-boned, I will eventually be pulling it, but a bit low on the priority list at the moment. I have thought of either replicating it with my desired changes or modifying it, before installing on my 86.5, but again it may be a while. The main change I'm looking at incorporating is changing to a standard receiver in place of the proprietary Euro coupler, so that I can mount a bike rack. the other change that I would consider, though it only impact the installation on the car is to change (reverse) mounting bracket on the right rear bumper shock so the hitch could be raised up then slid left into position instead of having to remove the bumper shock to get it into place. I think this change would allow for installation without removing the bumper cover, so the only thing that would be required would be to drop the fuel tank for the install.

https://cimg9.ibsrv.net/gimg/rennlis...639a28fe6a.jpg

Thats absolutely a crack at the weld. Thats a horribly designed junction, and shows that the fore/aft bracing in place was inadequate.

We dont see a need to drop the tank at this point.

That is a shadow. There is absolutely no crack there. The plate that attached st tube to the bumper mount is formed so there is a 90 degree bend in the bracket that is casting that shadow. The fore/aft bracing extends all the way forward past the fuel tank, which is what drives the removal of the fuel tank for install.

Then we disagree.

Thats most ceertainly a crack, theres nothing there with light from that direction to cast -that- shadow, to identify as a metal fatigue crack. It even extends into the weld itself.

No way, IMHO, and my fabricators opinion, is that a shadow...there are sharp lines, surfaces, and patterns that match _so_ perfectly, for this to be a shadow (from nothing in front of it) to be a crack.

It's a crack.

https://cimg1.ibsrv.net/gimg/rennlis...37358eed03.png


You can see why its there, in the drawing and image here below.

ALL of that stress is in the attachment of the reinforcement down to one small tab..with a big fat weld on it.

The other 90% of the attachment to the mounting bracket is not sharing in any of the work here.

https://cimg2.ibsrv.net/gimg/rennlis...a6c86815ba.png
https://cimg3.ibsrv.net/gimg/rennlis...9000c757e2.png

As a dual major in metallurgical and mechanical engineering, and someone who has supported a major airline doing failure analysis and accident investigation (for example), I can verify that without a doubt that is a shadow caused by the flash on my phone not being concentric with the camera lens. The small tab is what is causing the shadow that you are trying to identify as a crack. If you notice the horizontal tube is also causing a shadow which extend up across the mounting bracket as well as along the bottom edge of the body and across the fuel tank vent line.

To help visualization, the red line is the edge of the hitch assembly illuminated by the phone flash. the green line indicates the shadow edge caused by the hitch assembly which corresponds with the area below the red line which has the flash illumination blocked by the hitch. The orange circle is on the area where the tube shadow is crossing the fuel tank vent line. In this area, if you zoom in, you can actually see that the vent line didn't crack of but is faintly visible in the darkness of the shadow.

https://cimg5.ibsrv.net/gimg/rennlis...307b0a709a.jpg

If its yours, remove it.

Put in proper light.

Theres nothing there making that "shadow".

Everyone can see where the light source is, and nothing is casting a shadow there.

No list of professional qualifications is required to understand where shadows come from.


PS, you forgot to explain away the crack in the weld at the bottom.

Either way, it doesnt matter, the drawing itself shows why theres probly a crack there.

Remove it...then we will all know for sure.


Remove it, put it on a bench...until then, even as a friendly debate, there exist a probability we're looking at a failed unit with a weak design point that can be done better.

https://cimg4.ibsrv.net/gimg/rennlis...a6bf6ac4a6.png

Still doesnt explain the crack apparent in the weld.and I can see the direction the flash is, and where the gusset doesn't not sit between the flash and the material.

Pull it.

I agree there's a crack in the root of that weld.
As for the shadow it's like one of those trick pictures where once you see the thing you didn't see you can's not see it. I thought it was a tear too at first.

Pulling the bumper isn't hard..solve all this in about 30min.

That crack in the weld is functionally the same match to the failure in the gusset.

The tongue weight and/or fore/aft stress is all in -1- small area in these design photos, for this implementation...IMHO.

There is no explanation of for the crack because the crack doesn't exist, neither the large gaping crack perceived by Speedtoys or the weld root crack mentioned by G8RB8 (both are shadows. I know you think that everyone can percieve the lighting angle anknow that shadows cant exist here, but apparently everyone can't.

Don't worry though, I'll be pulling it, not because it is cracked, but because I need to transfer it from my 85 to my 86.5.

Someone of your qualifications should be able to pull if off fairly quickly then.

I'll take the Mark I Mod 0 eyeball assessment over what I can discern in a picture.

Home Made Tow bar
 

I made my own based on the pic posted by 'Porken' with mods to stop cracking that was also posted.
It wasn't that hard but I did have the car stripped.
I can remove mine without removing the fuel tank.
https://cimg6.ibsrv.net/gimg/rennlis...e6a68f61c6.jpg
https://cimg2.ibsrv.net/gimg/rennlis...9b0175a3ba.jpg
https://cimg4.ibsrv.net/gimg/rennlis...f910ba2936.jpg
https://cimg7.ibsrv.net/gimg/rennlis...d04204b13e.jpg
https://cimg4.ibsrv.net/gimg/rennlis...f40665d131.jpg
https://cimg7.ibsrv.net/gimg/rennlis...7c9d1370b0.jpg

That looks really nice.. i see you fabricated the bumper mounting brackets both open to the left, that is one of the changes I would have liked done to the factory hitch. It would allow the assembly to be installed without removing the bumper shocks to get the hitch between them, which would installation much more convenient.

it may not be an issue removing the factory hitch without dropping the tant, but would have been incredibly difficult to install it the first time without dropping it. Primarily due to limited access for aligning and drilling the necessary bolt holes.

People keep referring to mods to address cracking. The pictures above in this thread are of my factory hitch, and there are no cracks in it. Everything people have interprerated as cracks are actually shadows.

What do you tow with this?

Well, I have $1 that says you'll be re-thinking what that stress fracture means from that incomplete weld at the mount/bar junction. That's just an incredibly poor way to attach those two pieces there that placed a lot of load across a really narrow path...we think.

We do agree it's a shadow, a shadow of a fracture. There is no matching un-even hardware between the light source and the black pixels there...some of us don't think. Its good for a beer when its off and visible. ;)

None of this is saying you did anything bad..just that we'd all love to see what you see, when it's off the car.

This is more how that should have been tied in, not simply connection that terminates -at- the stress point where the metal will, some of think we see, fatigue. There will be a few passes to fill that weld gap to move load up the plate than sit in the placement weld there now.

https://cimg1.ibsrv.net/gimg/rennlis...4212e44c8f.jpg
https://cimg2.ibsrv.net/gimg/rennlis...af21ad9234.jpg

If we travel any distance, my wheelchair and shower chair. With both, my wife thinks there isn't any space for clothes!

Cool..thanks for the pictures. It answered a few question I had over the older other drawings.

I think I'm done..some last finishing bits, more pics once done in two weekends. Lots easier with the car apart. :)

So, the 'million dollar question':
When are they going into production?

Myles

We would like a pre S4 Car to verify a few assumptions. And then we will decide.

Location?

San Jose area, shop in is Santa Cruz.

Looking for a volunteer to confirm Pre-S4 fitment this coming Friday in Norcal.

Not the best photos, but, all done and completed, and installed.

Gallery:
https://www.flickr.com/gp/28804666@N08/W520PW

Happy to answer any questions.

If you're selling these, please put me on the list.

I'll probly start a dedicated thread..but..we need the car. I'll finish the wiring this week, put the ball on it for a few more pics.

Per-Chassis Challenges:

• The slot up between the battery box and the gas tank . (VERY tight, but is in contact with neither the box or the tank)
• Leaving the bumper mounts aligned right to fit the crash bar
• The four rear tub holes you need to drill exactly (so the clamping plates do NOT slip)
• The last final-step (once everything else above is aligned and set and torqued) two holes drilled to fit the main bar to the longitudinal (fore--aft) and tongue weight brace..also exactly so there is no slipping....

We need the car. This will be built -to- a specific car and it's specific differences. In the same model of 928, I can think of at least four places where there will be 1/16" difference in where things end up, each, on three different planes.

We have a whole cut out tub to develop with, and its the "same" but it was not the same as mine..you'd end up with a handful of washers to soak up space, and inner clamping plates that wouldn't sit right (sheet metal forming differences plus the amount of dum-dum applied)..probably..and certainly with a few critical holes that would not be concentric and in the right place.

Nobody wants to sell things that require user fabrication to make fit right.

From S3 to S4 (in the two tubs we reviewed), there is 1/4" of difference between where the longitudinal brace meets the main bar...for example. To use a spacer/washers to soak up the difference, makes a (mostly) tight clamping load across two places, turn into a (much more) shearing load across two bolts quickly..and, that will lead to unhappiness.

You want more welds, with fewer bolts in the shear space..as you can get.

Someone sent a PM "Whats the tow limit?"

Good question.

Well, -I- cant think of a situation, that with the trailer weight plus gear on it, I would have over 1500 total pounds behind the car.

The acceleration rate to make 0-100mph in roughly 15 seconds, would be .3g, which would be...an extensively stupid thing to be doing, and with the trailer, a lot more HP than the every day 928.

That math, says that is a pulling force of 6120N, or 1375lb...plus some losses for the rolling friction of tires on good pavement, a coefficient of 0.01 perhaps. Not much.

A more reasonable, but still just as unlikely acceleration of .2g, would be a pullbar load on the hitch of 2720N, or 612lb. So this would have to support a steady load of "Two Speedtoys, plus some groceries"..racing. Silly. Tongue weight, is a non thinker..unless you did something unusually wrong, shouldnt be more than 135-225lbs on there for up to a fully loaded 1500lb trailer. (9-15% of trailer weight)

Four 10mm high strength bolts, torqued properly, with tub steel at the front of the spare well against the corner of the front of the box, and in the rear by the rear of the tub 'box'..with roughly 8" of plate clamping area...that's a fair amount more than the 600lbs of accel/braking force required. Each bolt has a shear rating of ~12000lb. So the bolts are fine, its about the shear forces across the clamped plates, roughly 10^2 inches with two bolts per plate, 10mm diameter, 75ftlbs. Its a lot. This works to deal with the low duration shock load of leaving a light hard with slack in the hitch, or a hard braking.

Honestly, other than my bike..I cant see more than 750lbs of bike + trailer behind the car. But I'd still feel OK wit a Uhaul 4x7 utility trailer with some gravel in it..just being more cautious.

After all, I/we are more looking to do this:
https://cimg8.ibsrv.net/gimg/rennlis...3cf5c54397.jpg

Not this:
https://cimg6.ibsrv.net/gimg/rennlis...45f1b0e522.jpg

U-Haul Tow Hitch
 

With the recent activity on hitch development by a few people, I thought I would share this information on the U-haul hitch I recently received. I confirmed they are still manufacturing this rack. I have no affiliation with this rack, I just wanted to share the resources with the list. I've added the technical drawing below and attached a Installation Instructions PDF, as well. Hope you find this useful.

Personally, I don't think this is nearly as well constructed or as strong as the units developed by @Speedtoys (Trailer Hitch Done..But Not A "Kit") or @76FJ55 (post above) but this may be an alternative for those wanting a kit.

This rack is for 1986 and earlier cars.

U-Haul Tow Hitch
Part Number- UHI24952CH
$179.95

https://www.uhaul.com/Locations/Imag...3e7=1268907331

Sportframe 1 1/4 inch Rec (Powder Coat)

• Class 1 hitch
• Max weight: 2,000 lbs.
• Manufacturer Part Number: UHI24952CH
• Part number: UHI24952CH
• Hitch image shown is for display purposes only and may not reflect the actual hitch for this vehicle.
• Please note:
  U-Haul is the only known company with a hitch that will fit your vehicle. However, these trailer hitches are built as ordered, so please allow 6 - 8 weeks to complete the manufacturing process.

https://cimg6.ibsrv.net/gimg/rennlis...6464a5076b.png

I posted the U-Haul hitch upthread, but at the time it didn't specifically say it fit the S4. Have you installed it?

Wait..this hangs from the bumper shock bodies? And then..pulls on the rear suspension cradle (The camber eccentric bolt) for pullbar load?

I could care less what someone buys, but this is a steaming pile of **** that someone was allowed 15min to design.

I wouldn't hang a tongue load on the bumper shock _body_, which is only now held to the car by the upper 8mm bolt...and on a lever arm and not as a shear load.

If that will pull 2000lbs...

The upper bumper shock bolt screws to a captive..and I mean _captive_ nut. It this get annoyed/yanked/disturbed, you're making some holes somewhere, to attempt a repair. The lower bolt is a washer/nut super easy to get to, but its the upper you _dont_ want to cycle load on and off of. You'll eventually I think, fatigue the spot weld on the nut.

If these were to be for load, IMHO, you would replace these to be M10 grade 8 or 10 bolts. Not the cheesehead OEM bolts which are only meant to locate the shock and bumper brace.

Mike --

You may have a little more fabrication ahead of you. A 5-6" --really-- stiff piece of 1/2" x 4" steel angle to wrap around the forward bumper shock mount, one for each side. Horizontal on the bottom, drilled to match the clamps arms on your hitch. That will get th weight off the shock body. I suspect that the design is intended for cars with rigid links where we have the bumper shocks.

There's absolutely no longitudinal strength to rely on at the bottom center of the rear suspension cross-member/gearbox cradle. Depending on that for fore-and-aft loading is not at all a good idea. It would have value neutralizing some tongue weight and maybe some lateral load on the ball though.

----

When I was growing up, the family Big Chevy Wagon got a 5/8 x 3 x 14" or so bar hitch that was suspended at the bumper with a really small bracket that doubled as the safety-chain catcher. The front end had a couple bolts through the rear-facing third-seat footwell tub with a backing plate. A couple 3/8" bolts at the bumper attachment, a couple more to the backing plate. That's it. 2000lb Weight rating with a 1 7/8" ball, a rating we stretched by throwing 6 kids worth of gear into the full-height tent trailer. Back when steel was good.

My little dirt-cheap folding utility trailer has a draw bar that's 1.5x2.5 of 16ga steel channel with rolled bottom edges. The "frame" is 1.5x4 16ga steel channel, no rolled edges. Formed up in a press brake. Has a 1200lb rating, whatever that means. It's a flexible-flyer I'm sure, but still manages to carry a couple yards of soil, half a yard of gravel, tires, furniture, jet skis, etc. when needed. The trailer hitches you guys are making are way stronger than the trailer I have. How strong is 'strong enough'?

I suppose it could be worse...

https://cimg1.ibsrv.net/gimg/rennlis...9363931048.jpg

You sure that's not "How to Give a Hand Job"?

No reason it shouldnt work. The bumper shocks are different in their overall shape, but not at where you would use mufler clamps to hang the hitch from....FFS..ugh..

:roflmao::roflmao::roflmao::roflmao::roflmao:

Yeah, but I don't need much to pull a little teardrop camper. I was, and still am dubious though. That's why I haven't jumped.

Maybe you'll be OK hanging a few hundred pounds off the shocks..

But that fore/aft bracket, that's going to taco if its ever asked for a Jesus Stop. Its way too long, and way too "not straight". And nothing was ever in anyones head to pull or push a 1000 load fore/aft on the rear suspension cross member...in it's design. At least the Porsche design is pulling, pushing, etc..through chassis metal, at the front and rear of the rear chassis spare tire box. Strong stuff.

Since U-Haul has deep pockets and warranties the work I suppose the thing to do would be out of the gate load it up, floor it to 80, then set the slips and see what happens.

Variation of an old idea
 

The designs that Jeff and others have made that recreate the factory design are really fantastic and well designed. However, these awesome designs using a receiver below the rear bumper pose some challenges for many rear mounted bike racks. I mocked up two racks (1 Up USA and Yakima Hold-up) into the location where the receiver would be. The tongues of the rack would not reach that far under the bumper without interfering with the rear bumper. The receiver is too low and tucked too far under. Adding an extension to the receiver is not desirable because it increases the bottoming-out on the rack when pulling into driveways since the extension makes the rack closer to the ground as the front of the car goes up the incline of the driveway.
https://cimg2.ibsrv.net/gimg/rennlis...5ecb317129.jpghttps://cimg8.ibsrv.net/gimg/rennlis...ac55f969d4.jpghttps://cimg9.ibsrv.net/gimg/rennlis...65a9c862dd.jpg

Since my needs are purely for a bike rack, I decided to adapt an an idea that was previously discussed. I spoke to two owners of this hitch style and they both indicated long term use of this design without issue. No damage to the cross member, no damage to the bumper shocks and no loosening of shock bolts. Additionally, on the boxster/cayman forum, mounting the receiver to the cross member is a fairly common hitch solution.


https://cimg9.ibsrv.net/gimg/rennlis...da7ea2b791.jpg https://cimg0.ibsrv.net/gimg/rennlis...e037a527df.jpg
https://cimg1.ibsrv.net/gimg/rennlis...aa2906808f.jpg

Here is how I adapted the design above, I decided to sandwich the cross member with steel plates on the top and bottom and brace the cross member internally with some thick box section tubing.

https://cimg1.ibsrv.net/gimg/rennlis...cf0a5e62c1.jpg
The bumper sits more or less flush on the cross member so the receiver was set flush also. I decided to use a 1 1/4" receiver tube purchased from e-trailer.com
https://cimg0.ibsrv.net/gimg/rennlis...acfc33d703.jpg
https://cimg3.ibsrv.net/gimg/rennlis...c7ed3faccc.jpg
According to the rack specification, the receiver needed to be at least 5" so it needed to protrude past the cross member.
https://cimg4.ibsrv.net/gimg/rennlis...1f4612dc2c.jpg
https://cimg6.ibsrv.net/gimg/rennlis...a28f8c51bd.jpg
The rack is shown at the minimum insertion line, but I have room to tuck it in further if needed.
https://cimg0.ibsrv.net/gimg/rennlis...cfdd1638df.jpg
https://cimg2.ibsrv.net/gimg/rennlis...1a63dd6001.jpg
https://cimg8.ibsrv.net/gimg/rennlis...3ab48e1cc7.jpg
https://cimg9.ibsrv.net/gimg/rennlis...bcceaa3f36.jpg
https://cimg1.ibsrv.net/gimg/rennlis...73daa5520c.jpg

I just thought I would share my progress thus far. I gave the rack a few good tugs and torques and even stood on it without issue.

I'll test fit the bumper before committing to cutting a hole in it. Hopefully I'll have an update by this weekend.


and here is the update. Drove 150 miles with 2 bikes and it was very solid

https://cimg3.ibsrv.net/gimg/rennlis...8bbf9b7e1.jpeg
https://cimg4.ibsrv.net/gimg/rennlis...cff5b92fd.jpeg
https://cimg7.ibsrv.net/gimg/rennlis...f1c223386.jpeg
https://cimg4.ibsrv.net/gimg/rennlis...c8da5970f.jpeg

They make receiver extensions...work well for camper shell equipped trucks.6.5.0

For anyone considering the u-haul option, here are a few photos of my install. It is worth noting that the forward bracket/brace design did not line up properly. Lucky for me, I had our man Stan (mrmerlin) do the install whilst my car was in for an oil change and maintenance. The install did require cutting and re-welding of the forward brace to fit properly, and removal of the exhaust (as was described to me). But the end result looks good and is unobtrusive.

Note - I intend to use the hitch for a bike rack only. I have been warned (by Stan) that it’s not a good design as he has noted in a separate post.

https://cimg2.ibsrv.net/gimg/rennlis...ec090e5cf.jpeg
https://cimg1.ibsrv.net/gimg/rennlis...24b0915e5.jpeg
https://cimg0.ibsrv.net/gimg/rennlis...c0742ddf9.jpeg

https://cimg8.ibsrv.net/gimg/rennlis...3d1543ef66.jpg

Nice!

FWIW I spent quite a bit of time installing this U haul hitch,

I dont recommend this part . the anchor bracket that went to the crossmember anchor was welded to the wrong angle ,
and the double U bolts hanging on the shock tubes removes the 5 MPH shock protection and could possibly damage the shocks once the hitch is installed.

I also told the owner that its poorly designed and the rear cross member could be damaged if you back into a curb and hit the hitch.
That said this is one car that should not be considered for towing
Other issues that could cause problems are the rear shocks being damaged from them bottoming out,
time will tell.

So the car isn't good for towing you believe, because of the Uhaul part, or the Uhaul part should not be considered for towing.

??

I dont think that the U haul part should have been passed on for installation for this car.
its a poorly engineered part and installed on pieces that were never made to have these loads on them

In general The rear suspension of a 928 isnt made to have additional weight on it ,
and as you can see the rear end is sagging in most of the pictures with a trailer attached,
this will in short order cause the rear shocks to be damaged from bottoming out
That said just because you can fit a trailer hitch to this car doesnt mean you should. IMHO
Though the picture of your black car with the trailer appears to be the best fit I have seen .
Now maybe if airshocks were used this would increase the towing capacity and restore unloaded ride height

I can put a bag of dog food in the back and have more weight on it than the trailer has on it right now too. This is maybe a 45lb tongue load. I wouldn't be too concerned unless passing 150lbs tongue weight. (Based on the drop I measured with my 280lbs standing on it)

If you overload the tongue, you can bottom it out.

If you overload it, a lot..I cant imagine a 3500lb capacity back there. My use case I cant think of ANY way I would have more than 1200lbs behind it.

The 928 is capable of quite some rear load!
I asked my wife to get me 10 bags of cement and 2 bags of sand. She thought I meant in one load!
https://cimg2.ibsrv.net/gimg/rennlis...e0caf1a563.jpg
Still more room in there.

Ya. But there's no room for a highway joint at 60mph.

Gary, I would love to have a copy of the plan.
thanks, drew

I'm interested

I'm in

Looks great. I did notice that you flipped the front half of the rack upside down. This makes sense to get the bikes lower relative to the body of the car, but doesn't this defeat the folding aspect of the rack when you don't have the bikes on it? After I get around to moving my factory hitch over to the 86.5, my plan was also to get a 1up rack, though I'll need to make an addapter from the factory hitch to the rack, I still think the 1up is the best starting point. I'll probably aim for a bit more clearance between the bike and car to eliminate any pedal to bumper contact possibility, and to be able to open the hatch with the bikes on.

Edit: That's a nice set of bikes you've got there as well. I'm guessing you do a bit of gravel with that S-Works. I just did the Mid South Gravel 100 this past weekend.

You're pretty close to Sean and Roger. Maybe one or both of them could be persuaded to make a few copies of your factory hitch while you have it off. I'd be a player for one.

Any news on this front? I like the bike rack idea. I'm looking to carry 2 65LB eBikes.

I really like Michael Benno approach.

Wonder if is strong enough to support around 200 LBs on a level arm that is almost 4 ft long. Assuming the torque would be approximately 100 LB at 1 ft and 100 LB at 2 ft. That would equate to 300 ft-lbs.

I'm putting one on my Cayenne first to see how well the eBikes travel on the rack.

Hi Simon, sorry I missed your response. Flipping the rack side plates required machining new locking grooves for the horizontal and the vertical position. I never got around to cutting the grooves for the vertical or stored position since I always remove the rack when not in use. Also, thanks for the comments on the bikes, my first passion. Hope your summer gravel rides went well. I just returned from 3-weeks Trans-Pyrenees gravel adventure (highly recommended).
https://cimg0.ibsrv.net/gimg/rennlis...604b15448.jpeg https://cimg7.ibsrv.net/gimg/rennlis...3bb398527.jpeg https://cimg1.ibsrv.net/gimg/rennlis...a20c0297f.jpeg


Each rack will have a max load rating. Not something I have been worried about with traditional bikes. But eBikes definitively is a whole different category and I'd recommend some research on that.

The hitch system I created is nice and suitable for the rack (50lbs) and two mountain bikes (60lbs) which is significantly less than your 200lb target. As I consider your weight goals and my understanding of the design I implemented. I would be a little weary of the viability of the design at 300lbs. I would recommend making a couple of enhancements:
1. A support that prevents torsional twisting of the bumper cross member (as the bikes bounce over speed bumps). This could be accomplished by a brace from the bumper to the body (eg exhaust hanger mount).
2. Replace the bumper shocks with the solid mounts 928-505-018-20 to better handle the additional tongue weight. I see this strategy with modern heavy duty OEM hitches like on your Cayenne. The bumper shocks are replaced with solid mounts.
https://cimg8.ibsrv.net/gimg/rennlis...c6f7786162.png
Solid bumper support 92850501820
https://cimg2.ibsrv.net/gimg/rennlis...624b3f42f8.png
Collapsable bumper support PN 92850501622

Michael, can I just ask, what is the receiver dimension? Is it for a 2" square hitch tube? It looks smaller, but hard to tell from photos.

Trailer hitch
 

I would be interested in a Trailer hitch as well

1.25" hitch. I purchased the parts for the assembly at etrailer.com

Thanks Michael. That explains how it looks.