'resonance' from power steering

[tim993]

Sometimes when maneuvering the car in the drive and I apply full lock at a slow crawl, I get a 'resonance' or slight vibration at the wheel. It's almost as if a valve / pressure bypass is opening and closing rapidly. Apart from that there are no apparent problems, leaks or lack of help from the power assistance.

Does anyone elses car do the same thing / or do you have any ideas what is going on?

I am told the racks were supplied by ZF, but maybe they changed over the models life. Perhaps it's a 'feature' of earlier cars?
Mine is August 1995.

cheers

tim

 

[Pickled Piper]

Hi tim993,
my 1996 C4 does exactly the same. I had it checked out and was told the resonance was from the hydraulic pipes to the steering rack. Apparently, it is very common and nothing to worry about.

pp

 

[John Maddox]

As PP - just check your PS fluid is full to the mark. If not top it up and monitor for leaks just in case.

 

[tim993]

Thanks PP / John. Okay I'll check that again. Though last time i looked it was fine and my car has always done this. The reason i asked was that I was talking to the chaps at GT-One who have also seen it on some cars - also with no apparent problems; however they did not know why it happens. I'm glad it is nothing to worry about! If it's the pipes, is it that the pressure comes in pulses and causes a pipe to vibrate / can the pipe be 'damped' or 'tied down' or something?

cheers

tim

 

[Pete B]

Mine was almost cured by fitting the rack brace (see TSB on fiting 18" rims). Apparently the extra torque makes the rack mountings creak and fitting the brace spreads the loads....

 

[Guards Red]

Fitting the brace is really easy and very cheap for a Porsche part so worth trying and good insurance any way. One of the otherthings worth trying is changing the PS fluid. Most will still be running around with whatever they were filled with at the factory and this will now be some 13 years old. Porsche now recommend Pentosin 202.

 

[tim993]

Hi Pete B / Guards Red - thanks for this advice as well. Is the rack brace a Porsche or aftermarket part and will it fit the TT, do you know? Also, is changing PS fluid a home or garage job?
thanks again
tim

 

[Guards Red]

Hi Tim,

it's a proper Porsche part. About 50 quid all in or less. Will fit a turbo but I would've thought it already had one. Can get you aprt numbers if intrested. You will need to get the allen head bots to go with it (two only) as they longer.

As for bleeding the PS, not easy as the pump will not tolerate running dry. Porsche empty the system by disconnecting a line front the front at the rack and letting it drain. The tank can be disconnected and turned over to drain it fully. To fill you need to pour Pentosin 202 (12 pounds from OPC for 1 lite) into the tank whilst cranking the engine (but not letting it start!) make sure the pump never runs dry.

An easier way is to use a turkey baster! You draw as much as possible from the tank using the baster, once empty you fill with fresh fluid and run the engine turning the stereing wheel side to side. Repeat until you've used the entire litre (capacity is one litre). This should progressivly dilute the old fluid with new.
Regards
GR

 

[38F3E1]

I think it's a characteristic of whatever tire you have fitted and the surface you are driving on. My car does it on tarmac with MPSC tires fitted but not with Contis fitted. It's the scrub angle of the inner tire on full lock that causes it. It will also depend on what geo setting you have on your car.

Ian.