Don Carter

The arm ranges on the Pro 9D are:

Front arm (short): 28"-41"
Rear arm (long): 39"-57.5"

So I definately have longer arms than yours at their shortest settings. Again, there are extra pads that fit onto the arms themselves, (you can see on the workbench in the far left of my picture) that can in effect provide a shorter arm, just haven't tried them yet.

blown 87

I need to take a picture of how I measured mine, I think the big difference is in the angle of the risers.

If I measured from the center of the swing pin to the center of the pad at its shortest setting I think mine would be about like yours, but both of mine have dead cars on them so I can not do that right now.

Brad W

Don, I see I have a PM from you and will also respond to that.
You are right about the arms being a tad too long for the front. We found that by useing a hockey puck on the front lift pad and that will help center the car on the lift point of the lift. I will put my car on the lift tonight and snap a picture.

Don Carter

I just noticed in the grainy iPhone pic I have of Brad's lift, the rear arms are extended 5-6". I'll try that this evening and see how the front's line up. I didn't have them extended at all.

(talk about too many Chefs...)

Brad W

see if this helps

Don Carter

Brad,

Thanks that helped me know where to position the car.

Got it all lined up to the jack points without anything but the stock arm pads. It just takes a lot of trying different positions. The garage floor is now marked to make it easier for next time.

I was able to raise it to the max height without hitting anything! (so much for taking it slow...)

Brad W

Don see if you can get a floor plate for the tire location. I just tell whoever to leave about 1 inch showing. I took some pics and looks like you got it. Here is with a hockey puck.

Don Carter

Thanks again for the pics and tips Brad.

That's an actual hockey puck? Looks like it's job is to focus the lifting on the jack point because the pad it too large?

Also looks like you have a spacer installed to raise the pad on the rear (long) arm to match the height of the puck.

Not sure where to find a hockey puck in TX but I may have to look into that.

pcar928fan

Don't you guys have a hockey team in H'town? Hell, we have one in Austin! Used to be the Ice Bats, they are something else now...not sure what...I have not yet gone to a game at the new location w/ the new team (probably the same old players though!)

jon928se

Don't want to scare you but a 4" slab does not seem thick enough to me unless it has a whole lot more reinforcement in it than you'ld normally expect. Even if the lift has a structural strut across the top of the posts (not just a cable tray) the holding down bolts are still stressed (pull out) when the car is unbalanced fore and aft on the lift.

I did the engineering work for a retrofit of a 10 lift workshop in the UK with some lifts up to 5 ton capacity (for delivery vans) and others just 2 ton capacity (about 4,500 lbs) even with the 2 ton lifts and with the original design data for the floor slabs the 6" floor was overstressed . Ended up extending the bases of all the small lifts with 20 or 25mm thick steel plate to get the floor loadings to acceptable levels and dug out and put new bases in for the 5 ton lifts.

StratfordShark

In the various photos the lift pads are on the jack points front and rear.

But in the WSM at the start, it says that for a "hoist" it shows photos with lifting arms, and states the front arms should be on jack points as normal, but rear pads should be on "rear axle control arm bracket".

For a trolley jack it says to use the normal lift points front and rear (and rear cross member alternative)

Why does it stipulate those brackets at rear for lift points? Are the jacking points safe to use all round with a lift?

S4ordie

Thanks Jon that is good to know. To make it clear, even with a 6 inch (152mm) foundation you still decided to increase the load footprint of the lift itself by inserting a larger base plate (1 inch / 25mm) under the feet of the lift? Porportionaly, how much larger were these pads than the base of the lift itself and how were these plates anchored to the slab?

I tend to over engineer things, my cars can attest to that, and when it comes to above ground lifts I am always a bit nervous. Especially in any region prone to earthquakes.

Cheers

Don Carter

Jon, Dan,

I have given this topic a lot of thought over the last could of months since I got the lift bug. I'm more of a closet engineer, not a real one though...

When I first started looking into 2 post lifts, I was amazed the base plates were not 3'-4' long to reduce the load on the bolts and the concrete with an unbalanced load. I looked and looked and noone makes one like that. I did see one on a Brittish car show where the mechanic, Ed China has one, but the plate was unpainted and looked like it was added on.

The manufacture specs require 4" of 3000 psi concrete for most of these lifts. You only see thicker requirements for very heavy duty lifts. I tested each hole after it was drilled and they were all 4-4.5" and there's rebarb in the slab, so even with cracks, it would take alot of force for a chunk to come lose.

With asymetric arms that allow the doors to be opened more easily, the car is shifted to the rear. For most front end heavy cars this may not be too far out of balance, but for the 928, it probably is. If you think about a 3600 lb car, with say 2200 lbs on the rear arms and 1400 lbs on the front, how is that extra 400lbs on the rear arms distributed? Of course it's a big lever so the forces are probably amplified some. Since the lift weighs over 1500 lbs, some of it is offset by the weight of the lift I would think and the rest pulls against 4 bolts, so less than 100 lbs per bolt. There are also 2 additional bolts mid way down the base plates that take some of the load, and the 4 bolts on the overloaded side are also working some to stop the tipping of the lift. (I know this reasoning is not exact since I don't know how to calculate all this, but just trying to think though where the forces are distributed)

If you search the internet as I have done for lift failures, it's hard to find cases of 2 post lift failures where the bolts pulled out of the concrete or the concrete somehow failed. I found one YouTube video from a show called Wrecked where a huge delivery van pulled a 2 poster lose and tipped it.

Anyway, I think if 4" were not enough and the baseplates were too small, there would have been lots of issues by now and manufactures would have been sued for their incorrect requirements specs and the specs would have changed. So I'm pretty comfortable at this point with the setup although it still doesn't look it should work to the eye...

Edit: ok, extra 800lbs on the rear arms, but the point is the same. Should have waited till after my 2nd cup of coffee to type that...

Don Carter

StratfordShark,

I'll check the WSM. That's interesting info and it would be great to have other options that might be easier to line up with this lift.

Don Carter

Found it...