Adrian WC

I recently had the opportunity to drive my 964 at high speed (legally!) and noticed that the steering was very sensitive at high speed. Just the smallest movement of the wheel would result in a dramatic movement on the road! Not very reassuring.

I suspect that something is wrong with the power steering as turning at lower speeds feels more cumbersome than it should and at higher speed, to light. Am I on the right track and what else should I have checked?

The steering, wheels and suspension are all standard. The alignment was also recently checked and confirmed OK.

Adrian

Dear Adrian,
What do you call high speed? I cannot give you anything until I know what speed you were driving at.
If you were at 160 mph then this is quite normal at standard suspension settings on 16 inch wheels with standard tyre sizes.
Aerodynamics and tyres are the big issue not the steering. The front end will lift at high speeds and you will start to lose traction on the front wheels as the weight comes off.
Ciao,
Adrian
964C4

Randall G.

You may be on to something, Adrian WC. This past summer, I had my rebuilt power steering rack (installed the previous summer) replaced, due to massive leakage. With the old rack, the car was uncomfortably (or irritatingly) darty on the freeway--too responsive to small corrections. This condition existed for at least several months before the rack started to hemorrhage severely. The car feels wonderful with the new rack, no more dartiness.

To be honest, I'm not sure what was going on inside the rack to cause it to act like it did. I'm pretty sure it had something to do with unbalanced (or over) assist, but I can't say exactly why? Something to do with the leak causing weird pressure fluctuations? Any theories out there?

Here's a photo showing where my rack was leaking, according to the shop that did the install. Sounds plausible, as the left-side gaiter (which is about all I could see)--while wet--wasn't squishy (full of fluid) when squeezed. When my original rack gave out, the gaiter was distinctly full of fluid. The picture shows the steering column spline, which is (of course) on the left-side the car for LHD.

Adrian WC

Adrian,

What you are saying makes sense to me. The lift generated at speed (240 + KM/H) should make the steering LESS responsive given my setup. My problem is that the opposite is happening. I have way too much sensitivity to steering input making the vehicle difficult to steer round bends as small corrections to the wheel result in big changes in direction on the road - contrary to what you would expect taking your description into account.

Is the power assitance supposed to be speed sensitive?

Randall G, thanks for the comments. I will have a look at the unit tonight and look for leaks.

Adrian

Dear Adrian,
I have to be quite honest here and say I feel you are mixing up steering sensitivity and impending loss of control. I know exactly the feeling you have and I am sure many other do as well. In fact my wife can even tell you. It is scary the first time it happens. You are reaching the limit.
Yes please go ahead and check steering racks and the like. If it is leaking fix it but if your 964 remains in its current configuration not matter what you fix I feel the problem will persist because it is not really a problem it is reaching the outside of the envelope. Lower the rear by 5 mm and the front by 10 - 15 mm and feel the difference.
Ciao,
Adrian
964C4

Adrian WC

Adrian,

Thanks for the feedback. I have driven at these speeds before (I also have an M3 as well) and do not have the same feeling. I agree that the ride height on the Porsche could be lowered to improve the handling at speed and is something I will look into in the new year.

Thanks again for the valuable advice.

Ade - C4 91

Hi AdrianWC,

Not discounting what Randall has said regarding the steering rack (as I had the same problem last year), I might suggest that you consider the alignment settings first.

You may have found this out already, but trying to get a 964 suspension set up correctly, especially for high speed driving stability, is a very tricky exercise, requires quite a lot of knowledge of the 964 and it's idiosyncrasies, and a great deal of time (usually about 3-5 hours).

In my experience - the people who know how to set these cars up are usually the specialists who set up track cars or have a larger number of 964s passing through their shops. I've been through several alignments - starting with an OPC's (who really had no idea at all) and finally getting it right with a specialist who had very accurate alignment gear (thanks JZM). Even then, only after several attempts with varying values of front/rear toe and caster, did we get it right specifically for my driving style.

After fitting Roock coilovers and setting up to Euro RS alignment settings, I found that the car was very nervous over 80mph and frighteningly unstable at 140mph. Decreasing the front toe out was the answer and the closer it got to 0deg the more stable (but less responsive) it became. In the end i settled for a compromise at 0'10'' giving reasonable turn in, where 0'05'' was rock solid right up to 145mph but felt too light into corners.

Lowering the car is probably the way to go, and will dramatically alter the way the car handles especially at speed, but it may not make your car easier to drive fast, just more predictable at the limit. Other changes that make significant differences are 17" wheels, changing the anti-rollbars and the choice of tyres.

Can you let us know what your current alignment values, as it would be interesting to know.

Good luck



Ade.

Adrian WC

Ade,

The car is going in on Friday to a guy who has the "right equipment" and "experience" for a Porsche. I will wait and see what the drive feels like then. I will post the alignment values on the weekend which is also when I will have time to take a closer look at the steering rack and related items.

Till then.

Randall G.

Ade,

When you had the same problem, was it accompanied by a leak? I'm not absolutely certain that the problem was related to the leak, or if I had a crap rack that just happened to leak. Though, I would think hypersensitivity would suggest hydraulic pressures not being what they're supposed to, caused by either internal or external seal leakage.

In my case the darty/hypersensitive handling was definitely caused by the rack, as replacing the rack alone cured the problem. Although, the car was realigned (to factory specs) after the rack installation...by the same people who did the previous installation (to factory specs).

When I had the dartiness problem, I felt as though people in other cars might think I was drunk, constantly correcting the car from side to side. I don't think it was that noticeable to the casual observer, but it sure felt that way to me behind the wheel.


Thanks...

Adrian WC

Quick update.

Last nights search(of all areas mentioned above) revealed the Power Steering resevoir was low (1/2 full) and that the ATF was a dirty coffee colour meaning it needs replacement. Futher searching found that the pipes leading to and away from the resevoir were all coated with fluid indicating a leak (common problem?) from resevoir to the PS motor (not sure where the pipes go to).

The fluid is being replaced to-day and the wet pipes will also be looked at and replaced if necessary.

Car will go in for wheel alignment tommorrow after the repairs have been carried. A test drive up the coast this weekend will tell if the problem has been solved :-)

P.S. The pan under the engine was full of ATF fluid which lead me to believe their was a leak somewhere. This will also have to be cleaned.

Randall G.

Hey Adrian WC,

When my rack went out the first time (shaft seal failed, filling gaiters), I also had a leak on the reservoir supply line at the pump. After the rack was replaced, this leak went away.

When I had the rack installed, I also gave the shop a new pump-to-reservoir hose to install. When I picked up the car, the new hose was still sitting in a box. Asked them why they hadn't installed it...not necessary, they said, my leak at the reservoir line was caused by high-pressure being where it wasn't supposed to be. Sure enough, the leak went away. I don't understand exactly how higher pressure was getting to the pump suction--must have been blowing by a seal.

Anyway, still take a look at your rack seals, if you haven't already. And, look at your pump--another common leaker.

GrantG

The standard 993 has a slower steering ratio that you may prefer, although some 993 owners have replaced theirs with 964 units for a more sporty feel (maybe a trade?). BTW, the 964 power rack is the same part as the one in the 993RS...