Imo000

Hmmm....... learn something new every day.

hacker-pschorr

A better test would be to lower the car, and loosen the four bolts that hold the lower control arm in place

I wouldn't go that far. It's a compromise most (if not all) performance cars have. How many street cars do you know of that come from the factory with 100% solid bushings?

Even the Ferrari guys are looking for solid bushings:

http://www.ferrarichat.com/forum/sho...d.php?t=263591

Here is the photo from the 2nd post:

Or these "pillow ball" bushings:
http://www.rhdjapan.com/m-tecnologia...rari-355-59516

Fabio421

Well maybe I got a little carried away w/ myself. What can I say, I was on a roll. But the old school rubber bushings are the problem.

Lloyd

The lower control arm rubber bushings do not provide any freedom of movement. They may provide great high speed dampening on the autobahn, but if you want to have a responsive track car it has to go. Remove as much rubber as you can with a drill bit then fire up a propane torch and melt the rest of it out. This is a real messy job. I machined the A-arm spindle on a Bridgeport Mill. Also made delrin bushings to fit. I have been running this car on the track with 2000 lb front springs and LEDA shocks for 4 years with no issues. I have some pictures I will try to include.

mark kibort

It might not be the shocks,but it might be the springs. after being in full droop, the compress and might take time to "settle". I dont know, but what I can tell you and can see with my hypercoil springs, is that there is really not any setting time. its low from the moment you drop the car. Now, with scots car, using the old springs (although cut), it still sits way high until its driven a long while. (or a few laps on the race track). maybe its a function of the stock diameter springs and those purches it uses.

chewy8000

Lloyd!

Thats exactly what I was lookng for. Delrin part #'s, measurements or where you got them please... I have a machine shop that can do the arms no problem. I just need a place to start with the delrin. I'm going to replace the upper A-arms with Carl's tubular units eventually and I think the delrin on the bottom is the way to go.

SharkSkin

Mark, as I mentioned before, you have a much higher spring rate, so the car is held off the ground by that considerable resistance offered by the springs. With stock springs, the amount of resistance overall is less, so the same resistance due to the bushings plays a larger part in the whole picture, relatively speaking. Also, it's possible that your setup does not allow the front suspension to droop enough to make the bushings take the new "set" that we see with stock suspension. What is the fully extended length of your front shocks, and how does that compare to an original assembly?

hacker-pschorr

That is awesome!!!

I recently swapped out the OEM rubber for poly on a non-928. You are correct, grab a torch and make a huge mess....

+1

mark kibort

I think you might be right there too, but it doesnt explain scots set up, with the same (near the same) spring rate up front. However, after pulling the holbert car apart in that area, i now remember how much stiction and binding the rubber bushings have. You guys are probably right. Its all in that lower control arm set up!

mk

Lloyd

Chewy, Set up the A-arm on a bridgeport mill with the spindle pointing up. Use an indicator to determine that z-axis is parallel with the spindle. Using a boring bar set up to the inside "trepan" the spindle. Remove a minimum of material, but enough to clean up. Put a nice radius on the bottom to relief any stress point. Measure the diameter of the A-arm spindle and make some bushings with about .003" clearance on the hole. One of the bushings will need to be split. Also , the OD of the bushing is important so you have enough clamping, but not too much. I have drawings somewhere, you may have to email me. I actually used UMHW plastic because it is really tough stuff and it machines much better than delrin.

wildwestsydney

How rough is the surface after the rubber is removed? Was it machined? How is the rubber bonded to the aluminum?

Sam

chewy8000

I wish one of the vendors offered these. I would buy them in a heartbeat.

hacker-pschorr

The issue for most vendors is the modification to the control arm, so to offer a complete package would need to include some kind of exchange for arms too.

I have never seen a lower control arm with the rubber removed, so I have no idea what is all involved. I have a set of S4 lowers I was sent by mistake (when I purchased some uppers.....non vendor purchase). If I get bored this weekend I might fire up the torch to satisfy my curiosity.

BC

The lower control arm is sort of ribbed on one of the cast shafts. I do not remember the other. I replaced mine on the S4 arms I had with a sort of blue urethane bushing. Whether it holds up, I will not know until I get the drive the car (finally!)

Erik - I did not need the torch. I simply worked and worked at it until it came off. Obviously the one with the metal outers - will be a bit more difficult.

I think machining down the shafts is a good idea - though I would not want to go too far. I assyme the inner ridge between the body and the shaft is specifically radiused for a reason.





The ones I have I don't think are made any more. I would probably replace them with delrin if they failed quickly.

hacker-pschorr

Delrin or UMHW that Lloyd used is cheap enough. I know we have a couple of places in our area that could pump them out for a reasonable cost. If we can put a rough cost on machining the lower A-Arms, this could be a reality rather quickly.

I'll be chatting with Todd soon, take a look at some lower arms with him & figure out a game plan.