81 SC Lowering Issue

[jhoughton]

I am in the process of lowering my 81SC and have run into the following problem:

After indexing the torsion bars on the rear and getting both sides to a ride height of 24" and 24 5/8 front. The right rear shock seems to be making a thumping noise like it has run out of travel? This happens when i push down hard on the rear bumper to settle down the ride height. Is the shock dead? They are stock along with the torsion bars. Have I just lowered the car too much?

The car is going to be 50/50 autocross and street.

Any help is appreciated...

Thanks in advance...Jay Houghton

[surflvr911sc]

24” seems awful low, although there are quite a few guys that lower that much but they usually have rebuilt their suspension.
Maybe try bumping it up to 24.5”-25” and see if it stops. I don’t think I would try going below F-25.5”/R-25” without new shocks, bushings, torsion bars, etc. For a 50% AutoX car you will want to do those anyway.
If the shocks have been there a while they should probably be replaced. Don’t forget the Corner balance and Alignment afterward.

[Joe Bob]

Could be a dead shock....got any records on the car? When were they last replaced? Could be time fer sum nu Konis DooD....

When ya get a bowl of lemons....make lemonade.....

My car has been lowered to 61 & 62 cms. App 24 inches at the rear and 24,4 at the front. At first my 9x17 245/40 left rearwheel rubbed (when accelerating hard out of a curve), but then the camber was made more negative which helped. I have Bilstein Sport shocks. Standard torsion bars.

[vesnyder]

Jay - If you have the original shocks you should replace. I have an '83 and replaced the shocks recently with Bilsteins. When I removed the old ones they came out in pieces! I suspect your old ones are shot. The ride will be remakably better with a new set - money well spent in my case.

[RANDY P]

Shot shocks. I'm at your height w/ same year and no problems. Have 1.5 neg. camber in rear on 16" x 8".


cheers.

rjp

[david c.]

your ride height will be increased substantially by new shocks... something to consider since you've started down the ride height path. You may need to adjust the bars again if/when you install new shocks.

Good luck,

[kristian85]

Originally posted by jhoughton
After indexing the torsion bars on the rear and getting both sides to a ride height of 24" and 24 5/8 front.

That's too dang low for a street car. Wasn't designed for it. Get closer to 24.75, 25.25.

[masraum]

I would think there is a problem with the shock, but isn't there a rubber bump stop or something for the suspension that needs to be trimmed down when you radically lower our cars?? That could be part of the problem. Or is that only on the front?

[Superman]

1. A thunking noise when you push down on that corner is not a normal sound, and not the sounds of a worn shock. It is the sound of something broken.

2. Pushing down on the corner of your bumper should do almost nothing. With performance suspension parts, these cars are as stiff as park benches. With fresh factory parts, they are still stiff, just not that stiff.

3. Few, if any, other improvements can be made to your car that would result in a more noticeable improvement. Fresh shocks will surprize you very much with the improved ride quality.

[kristian85]

Originally posted by Superman
1
3. Few, if any, other improvements can be made to your car that would result in a more noticeable improvement. Fresh shocks will surprize you very much with the improved ride quality.

Hear hear!

[chrisp]

I am sure there are many differing feelings on this subject. Just watch out and make sure your ultimate setting suits your needs and driving conditions. Yes US issue SC's we're higher than their Euro counterparts. So it is pretty safe to go to Euro ride height. If you drive on roads or with a style that will use a lot of suspension travel don't go too low. Remember that the torsion bar is a spring supporting the car over the wheel. If you load the wheel the bar flexes and the wheel moves up towards the car. It's all about the rate of the spring and the amount of travel to gradually increase the load on the spring. With stock torsion bars the car will bottom much more easily than with a higher rate t-bar. That's why when cars are lowered the spring rate is increased. If you were going with 23mm front and 30mm rear I would say go as low as you want. The track cars are sub 24" rear. If you use a lighter t-bar like 22mm and 28mm then 24" rear is okay but I would say for stock t-bars then 24" rear is risky.
There's no extensive testing specific to 911's behind my logic but the spring theory is true and you shouldn't lower a car much more than 1/2" to 1" without substantially raising the spring rates. Unless you drive on a silky smooth highway made with something like 27 inches of cement and like 6 inches of pavement where cracks and heaves are dealt with by replacing long sections of highway....like the German autobahn (saw that one on TV).

[jhoughton]

I went ahead and bought all new Bilstein Sports and 22/28 torsion bars along with the bump steer adapter. Hopefully that will solve all of my problems.

[kristian85]

Originally posted by jhoughton
I went ahead and bought all new Bilstein Sports and 22/28 torsion bars along with the bump steer adapter. Hopefully that will solve all of my problems.

*ouch* A smooth, supple ride it ain't gonna be. And, it may not fix your problem. You should diagnose it accurately before throwing money at it.

[Speedy1]

I to just replaced the shocks on my 82SC with bilstein sports and the ride is much improved over the old ones not too stiff but not too soft. I am lowered also but I don't know how low. (Too lazy to measure) The thing that you hear is more than likely the rubber bump stops under the protective sleeve. My left rear came out in 300 pieces. A cool member listed a post for a tech tip on how to install new shocks on a lowered car and what to do with the bump stops. Basically the bump stop has 2 portions to it, a thick solid area and 3 ribs cut off the solid area of the stops and install the ribbed section only. If you bottom out your suspension during an autocross and it hits the uncut bump stops it'll send the spring rates threw the roof and possibly cause a snap spin in a corner. NOT GOOD! I hope this helps just my .02c worth.Speedy1 ooo yea good luck getting to the top of your shocks it was a bit**

[chrisp]

I have the 22/28 t-bars with Bilstein Sports and Weltmeister 22mm F&R sway bars. It is a very acceptable ride on the street (if you are accepting of a firm and noisy ride but one that is by all means fully street-able) and works well on the autoX and track. It is kind of an interesting set up because although it is a good balance between street and track it's major compromise to a pure street set-up and gives up time on the track to a better track set up. Since I use my car for both I was willing to accept the compromise. I think you'll like it. You're passengers may not however. My car is set at 25 front, 24 1/2 rear.

[kstylianos]

Check out this thread regarding the bump stops for front Bilstein inserts for Boge struts.

The external bump stops are not needed as they are internal to the insert.

Help needed fitting new shocks


2 Other links showing bump stop modifications for front bilstein insert/bilstein strut and rear.


www.smart-racing.com/pdf's/Rubber%20Rear%20Shock.pdf

www.smart-racing.com/pdf's/Rubber%20Front%20Shock.pdf