TD in DC

As some of you know, I broke my control arm at Shenandoah Circuit two weeks ago.

In purchasing replacement parts, I researched the rules for SCCA ITS class and for PCA stock classes to learn that suspension bushing material is free.

So . . . what to buy. How much of a difference do the bushings really make?

It seems like you have stock rubber bushings, aftermarket plastic bushings, or the high end metal bushings.

Which would you recommend? I am not trying to "fix" any problems in handling of my car . . . rather I am just in "while you are in there mode."

The whole car kit for the metallic bushings is $1,200. The front end only kit is approx $650. This seems like an awfully lot of money to dump into a n/a 944 if it will not make "that" much of a difference. On the other hand, if the difference is night and day, then maybe it isn't so bad.

Thoughts?

Larry Herman

Funny how most answers to your questions start with "it depends", but it really does. The purpose of harder/solid bushings is to locate the suspension more accurately. This will prevent deflection which can cause greater camber and toe change than the suspension design allows. Also the better you can control side movement in the rear suspension, the wider tires you can run without rubbing.

So it depends on your suspension design, and how sticky are the tires that you run. Street tires? Unless your bushings are old, forget about it. R compounds, run harder or solid bushings. Race tires require monoballs for best performance. Another item to consider is the suspension design. The farther apart the "locating points" on the suspension the more effective the bushing can be, so usually on Porsches, redoing the front is less critical than the back because of all the load on the rear trailing arms, and how close together those pivot points are.

TD in DC

Thanks Larry,

Your answer reminds me that I can provide some more information. This is for a 1984 normally aspirated 944 that runs Toyo RA1s for DEs and Hoosier slicks for races. I am running the early steel control arms, which I have had boxed for added strength. Sadly, that is exactly the type of control arm that snapped.

TD

P.S. Right now, I have plastic bushings. I need to inspect the current ones to see if they were damaged.

Larry Herman

Monoballs are good for suspension members that twist a little as they move through their range. 4 and 5 link rear suspensions require this. I assume that they last longer as well. Solid plastic bushings are fine for suspensions where the pivot points stay in perfect alignment (like on a 944 trailing arm or a 964 lower A arm).

924RACR

Hey, don't be so hard on that control arm - it gave its life so your car could live!!! I just badly tweaked my LF a-arm the other weekend, brushing the tire wall at 72mph. The a-arm wrinkled up pretty good, the spindle bent, and the caliper anchor bracket snapped at the bridge.

I replaced the spindle and caliper, bolted on a replacement a-arm, put the wheel on and checked the alignment. Perfect.

Start making the a-arm real stiff, you'll find out when the frame will start to buckle. Steel a-arms are cheap; buy the replaceable monoball bushings (which I wish I had - mine press in, not easy to switch between arms), carry a couple of spares, and be glad your a-arms aren't aluminum.

Besides, I think reinforcement may be against the letter of the law for IT (though I know some cheaters do it anyway).

Gotta have a fuse in the system. I've had the same experience bending rear control arms.

For the record, for an all-out race car, I prefer the monoballs, but will admit that the plastic will save a LOT of money...

TD in DC

Thanks Vaughan,

Yeah, it looks like the welds from the arm to the cylinder that connects to the crossmember pulled apart. This was on the passenger side. When it started to fail, right hand turns were hell, but left hand turns felt as if nothing was wrong at all, I assume because the load held the arm in place.

Where do you get the replaceable monoball bushings and, for that matter, the plastic bushings?

TD

M758

TD... this is the reason we don't allow metal bushings in 944 spec. They cost alot.

Rubber bushing work fine on street cars since they locate the suspensoin and provide some level of isolation from the harshness of the road.

The various plastic (delrin) included greatly reduce the fexibility of these bushings and therefore sharpen then handling of the car. With soft rubber when you turn all forces of the car's body must react throught the bushings. If they are soft then the response is dulled.

Now the plastic types are nice since the increase that stiffness at a reasonable cost. Metal "bearings" are in fact much better since they allow zero off axis movement, but allow plenty of unrestricted on axis movement. This great for creating precise suspension movement and handling response. Any top notch build car will use these.

There are downside to the metal bushing however.
They are inital cost and maintinence. You have seen the cost part. The maintence end is due to metal on metal friction. They need to be greased and maintained clean. Now I am not certain of the specfic requiredments of each particular unit, but most rubber or plastic bushings are install and forget types. Not so for most metal ones.

On my 944 spec car I run white delrin busings at the control arm to crossmember point. I tried to run weltmeister red poly bushings, but they did not stand up to the abuse in that spot. The delrin's have worked great for years and have outlasted one steel control arm. For the caster block I used the welt red bushing. Those seem to work fine there.

In the rear I used weltmeister black poly bushings for the t-bar carrier. I have been running those for 5 years and they seem to be perfectly fine. They do squeak like hell however. Very unpleasant if it were a street driven car.


I feel the plastic types are must for any racer. The rubber is just too soft and flexes too much. Metal is ideal if it were not for the large cost. Plastics are closer to $250-300 for the entire car vs the $1200. From a value angle the plastics are the way to go. Performance wise metals are better. How much better is tough to say, but they are better.

Couple points.

1) 944 spec (SP1) prep is allowed in 944 cup at 2600lbs. Basicly no changes to the 944 spec trim. DD seems to think it will be competitive at that weight. So far one car seems to be showing that. The biggest advanage of 944 spec trim is that you can run the toyos at race time and not need to spend money on hoosier or even metal bushings like a few cup cars have.

2) I got my stuff from Paragon products athough I believe Karl at racer's edge is one that makes the delrin front bushings for the crossmember. Infact it was about 2003 when It was busting through the welt red bushing and Paragon contacted Karl to make up some protoype delrin bushings. They went in my car and have worked extremely well. Cost was double that of normal poly bushings, but still much less than full on metals. I recommend these to all 944 spec guys with steel control arms.

chrisp

Was caused the control arm failure? Although I'm not that familiar with 944's, in general when a bushing has stiction it can cause problems. Instead of an control arm just being in compression or tension the sticky bushing will cause it to need to bend and it'll snap. This is where bearings are great, they let the system move more freely. Not only do you gain a level of performance becuase of the free travel but suspension components are less stressed in ways they don't like to be stressed.

Nader Fotouhi

Todd,

I went all out to spherical bearings and derling bushing everywhere I could a couple of yeras ago. But I also changed the entire suspension (more than once ). The difference I feel is more stiffness with less change in geometry which helps in corners. Remember all of these components must be matched and the guys that can do the best job of matching all suspension parts come up with the best set up. Unfortunately, I am still developing the car $$$$.

I canot remember whether the ITS rule limits the t/b and spring rates. I know you have to retain the t/b which if I remember correctly means that 31 mm t/b is the biggest you can use on 44 cars. Can you go to 400lbs springs with perches up front? Do some research on spring rate limits. If SCCA rules limit the spring rates, going with high end stuff does not make sense becasue the spring rate becomes the limiting factor.

BTW, I do not believe that box welding the a-arms is outside the ITS rules. It is a safety modification of stock component.

924RACR

ITS does not limit spring rates or torsion bar sizes - but they must be of stock type, meaning no rear coilovers. The biggest rear t-bar you can get is 34mm (hollow), which is what I'm running in my car (pairs well with 660# springs up front).

Safety modifications are not allowed unless specifically labeled. Reinforcement of stock suspension arms is not allowed, IIRC.

The "replaceable" sphericals are the type that are installed in a cartridge that screws together in place in the joint; Racer's Edge are this design (don't know if there are any others). My a-arm bearings are from Shine Racing Service, for the VW steel front a-arm, and are half the cost - $295. But you have to press them in, and they are not easily swapped like the cartridge-style (when you bend an arm).

My a-arm did start to tear at the leading edge of the front bushing tube. It was also bent backwards about 3-4 inches from stock location at the balljoint end. Yes, the tire was touching the wheel well.

Regarding bearing longevity - these are not metal-on-metal contact, obviously those wouldn't last long. They're teflon-lined sockets, and I've been impressed by the lifetime of mine. I put them on in 2000 IIRC, and it's now 2006 and racing hard (5-6 weekends per year) ever since. I check them every year, but no need to replace yet - still no slop.

I'm using the RE design spherical cartridges in the rear control arms.

Geo

As Vaughan has stated, this is not legal in IT. There is no provision in the rules to modify parts for "safety reasons." If there were, some very clever people would come up with some very clever modifications for "safety reasons."

TD in DC

It is ok. I run with 44 cup, which allows me to come in either through ITS or PCA rules, with certain additional modification allowed. I can bring my car in to 44 cup through PCA rules, and thus I think that boxed control arms will be fine for my racing venues, which include 44 cup and, now, PCA Spec 2 club racing.

Besides, I am fine with someone calling me on this if I ever were to race SCCA ITS. This is one of those "c'mon" mods that cannot possibly make me go faster, and they are easily replaceable.

RedlineMan

Hey;

Here's my perspective. What you use and whether you notice any difference has a lot to do with how stiff the chassis is and how tall a tire you run. The softer and taller you are running, the less you will notice. I run 16s with fairly stiff springs (500F/450R), home-made steel arms, and all solid bearings, and did not notice anything to speak of. If you get to 600+ and down to an 18" 35 aspect tire, you might start feeling it.

There are two choices in my mind: OE and Metal. Plastic bushings wear too quick for my interest level. Rubber and metal last "forever."

Vaughan makes an outstanding point about stress transfer. Not something 99% of people ever consider.

Most steel arms fail exactly as yours did, Todd. When you reinforce them, you also need to wrap a strip around the bushing barrel and weld it up. This is often overlooked.

John Brown

It's only money Todd.

Joe P's setup is the best value. Full on metal is ultimate.

80/20 rule is in play big time. First 20% of the cost gets you %80 of the performance. Is it worth the extra (to you) and could you really tell the difference??

We tend also to forget that if you are someone who has a shop install this stuff the cost of parts may be irrelevant or at least masked by the instalation cost.

kurt M

I was going to ask about this. Other than wraping a shipping strap around the arm to get the car on the trailer I have not had a good look at the failure or fail mode yet. The arm came apart form the barrel. The barrel was not frozen in place as it turned in my hand while I was straping things back together.

Is this a common failure? A quick look at the arm showed that the sides of the swing are were beefed up as was the sway bar hookup point but the arm the bushing barrel was not overlaid IIRC. I was talking to TD about this and brough this up as well as an easy fix but did not know if this was a common or uncommon failure.