Could bad shocks be my problem?

[D911SC]

I am trying to tweak the handling of my car (road use only) and while I have made some improvements it's not quite right yet.

The symptoms are that the car seems to wander a bit under hard acceleration - it feels a bit unstable. It's like the front is lifting. Again it seems a bit loose under heavy braking, but the acceleration is what is more noticeable.

On long sweeping bends the car sits quite flat but again it seems to wander a bit. It's like it is shifting from oversteer to understeer and back again.

I recently refurbished the car and did the following to the suspension:

1. New ball joints
2. Steering rack rebuilt (done by my mechanic)
3. 22/28 hollow TB's
4. New rear drop links
5. All new poly bushes front and rear including spring plate (they dont squeak!)
6. Turbo tie rods with 'spacer' bump steer kit

The was aligned by a specialist referred by my mechanic and he set the toe to straight at the front and 1/16 toe in at the rear.

Aside from using the standard sway bars the only moving parts on the suspension I didn't replace were the rear shocks and front inserts.

Before I pull the trigger on new shocks to solve my issue I'd like to get some feedback if this is likely to be my problem. It's hard to say if they have ever been replaced before but when I pulled them out they looked pretty old.

I have the Bilstein Sports (green), no rear tail but I do have a front chin spoiler.

Thanks.

[Rot 911]

I suspect your problem is the toe on the front. Stock I believe is -1/4. Neutral or positive toe can lead to the sensations you are describing.

[D911SC]

Thanks Kurt. Perhaps I should organising another trip to the alignment shop.

Darren

[ganun]

Per the Tech Spec Book front toe in is +15'+/-5' per side.... that is 1/4 (0.25) degree per side.
Then assuming 16" rims:
SIN (0.25) = X / 8"
8sin(.25)=X
X=0.35" toe in per side (about 1/32") and total toe would be ~1/16" measired at the rim.

George Nunez
Miami

[ganun]

My mistake with the decimal ....it should be 0.035", obviously NOT 1/3" per side!
George Nunez
Miami
Its late

[D911SC]

Thanks George.

I'll take these numbers and get another alignment done.

Is it possible that my shocks could be contributing to the issue? I guess another way of wording this question would be to ask what symptoms I would experience by running worn/old shocks - front and/or rear.

Cheers,
Darren

[trond]

Based on my very recent experience with wrong tires causing wandering front end and loose rear end I would suggest you look at the tires ? I thought I had a bent chassis or something out of order with the suspension but when I changed tires all stability issues were gone

[D911SC]

Thanks trond.

I am running Bridgestone Adrenalin RE001's on 16 inch Fuchs (7s and 8s). They are 205/50/16 and 225/45/16.

They are near new.

[trond]

The tires that I had to replace because of lacking stability were also new. Fronts were 205/55-16 Michelin Primacy HP and rears 225/50-16 Goodyear EfficientGrip
The car was very unstable and unsettling especially in fast corners. Your description on how your car feels as if it goes between understeer to oversteer sounds very similar

I got the car back from alignment & corner balance same day I got the Goodyear rears and having changed several things I did not understand why it handled so bad. As part of troubleshooting I reluctantly agreed to try a set of track day wheels (w/some soft compund Federal tires) that had worked well on another 911 and handling was restored.

There are brands/types of tires that does not work well with the 911. Don't know about yours. Could be a bad shock as you suggest

[McLaren-TAG]

Okay, you've asked a number of times now but reading through the responses no one has given you a direct answer to your question. The answer is yes, your shocks could certainly affect the situation you're describing. But the answer is not as simple as that since you've seen the other responses.

Tires and alignment also play a part (a more impacting part IMO) than shocks, so it's worth to look at those first. Suspension is part art and part science and every suspension component change has a ripple effect on other suspension components.

The primary job of a shock absorber is to keep the wheels planted on the road surface, preventing them from hopping and keeping the car from leaning and rolling too much. In other words the help to balance each corner of the car.

You've changed just about every other component of the suspension because it was tired, why not just go ahead an do the shocks, it's only going to help the overall effect of the other changes you've made. But it may not be the source of the issue you describe so it's prudent to try tires and alignment first.

[tobluforu]

If you are not use to zero toe, then this could be the issue, period. If the car is not corner balanced, then this can contribute as well. If you have a wing on the back and no dam on the front, highway driving at speeds can be downright fun as hell. There are a lot of factors in regards to setting up ones car just right; took me years to really dial my car in, only to screw it all up again when I changed ride height, front shock, etc. It has never been the same since, should have left well enough alone. How old are the bilsten sports, and yes it could be the shocks, but I loved my old boge shocks in the front that were 12 years old paired with koni adj in the back.

[Driven97]

It's important to understand what's going on as well.

With toe-in, the front tires are constantly lightly loaded, opposing each other, towards the center of the car. This gives straight line stability.

With toe out, the tires are also lightly loaded but opposing out. Under perfect conditions, these forces would cancel, but road variations cause one tire to have more say than the other at times, and you get to make corrections going down the freeway.

With zero toe, the tires are actually unloaded. Even with new components there is a slight bit of give, and the sensation of the tire loading and unloading with road variation can be more unnerving than toe out.

EDIT - there's also a chance that the shock shaft / seal is worn. The strut gives physical location for the front tire, so even a small amount of play will be noticeable. I once returned a car to an alignment shop three times unhappy before they figured out that my strut shaft could wobble in the body.

[kjchristopher]

Did you replace the bushing on the trailing arm as well?

[D911SC]

Thanks for the responses.

Judging by some of the other parts I replaced I would not be surprised if the shocks were original, which makes them 30 years old (135K miles).

With the shocks installed is there any way of assessing their condition?

kjchristopher - yes I replaced the trailing arm bushing.

[Jonathan S]

Have you checked the Ackerman? If one front tire is turning in more than the other then you will get an unstable attitude in turns as they fight each other. Center the steering and measure toe, then sweep left and measure distance between inside tires, then sweep right and measure the same they should be equal to left sweep.. If you have a greater variance between left and right then one wheel is turning farther than the other causing an instability. I am not an expert, but that should give you some idea of whether they are close or totally out, then an alignment shop could properly set it.

[krisjkr]

I thought I had a bent chassis or something out of order with the suspension but when I changed tires all stability issues were gone