964Andrew

After 2 MB PS pumps and reverting back to stock cam driven pump and having each time after the swap excellent steering feel, months after a tightness in steering returns (particularly when turning left but not always in the same spot on the rack). The last is on all OEM Power steering setup and spec geometry.

How the tightness feels:
More noticeable on cold engine early in the morning. When turning left from straight, first half of the turn goes well, then the steering wheel tightens and after extra force is added the steering feel suddenly returns to normal. It doesn't always happen in the same spot on the rack and the same angle of turn. After the car warms up the tightness is still there but barely noticeable.

- The power steering rack was rebuilt with new seals, before rebuild on old seals same tightness was noticed (2 years, 2 different PS setups since then) - no leaks
- Rebuild OEM lines - no leaks
- Cam driven pump - no leaks, no weird sound
- Porsche spec PS fluid - flushed and new
- Pump to reservoir lines refreshed - no leaks
- Steering linkages - all new Elephant Racing (2 years, 2 different PS setups since then)
- Replaced all bushings and joints with new (2 years, 2 different PS setups since then)
- Rennline camber plates ans spherical bushings (3 years, 3 different PS pump setups)

Two ideas as what is happening:
1- problem with input shaft, maybe blocked passages?
2- worn OEM power steering pump

I need help with this, what's happening?
I have replaced 2 MB pumps and went back to OEM setup and unless I'm encountering the same problem 3 times in a row the problem is somewhere else.



Thanks!
Andrew

Rocket Rob

Have you fully bled the system? To do so, with the engine running, turn the steering full lock to lock a few times. When I rebuilt my PS pump, I did this 10 times, just to be sure.

Also, what is the condition of your steering column universal joints? And the front struts, tie rod ends and ball joints?

964Andrew

System is fully bled. Universal joints have zero play in the column. With the wheels on the ground, car running I had my hand on the steering shaft down under the dash to see if I can feel any incorrect movement. None detected. Tie rods and ball joints - new. Both replaced 1.5 - 2 years now (2 different pump setups since then, same behavior). Front struts, top mounts also new.

Thanks!
Andrew

jwbavalon

Andrew, I would recheck the steering u-joints. Although they have zero clearance, do they move smoothly?. If one is stiff it could give the sensation you are experiencing.

964Andrew

OK, I will. I'll put a camera there to see the operation.

Thanks!
Andrew

apanossi

Wow! Not sure what to make of this. I have been going on 20k miles on my MB pump with only a small weep of fluid at the base of the pump itself. The steering is still fantastic. There must be something downstream from the pump that is increasing pressure and causing the pump to fail.

-nick

Is it similar to this?
https://rennlist.com/forums/993-foru...turn-left.html

That’s 100% a rack issue.

My Merc pump has been working without issue too.

964Andrew

Thanks, just read through the thread. It sure sounds very similar. If it is the rack then this sure sucks big time. I don't even want to think about the possibility of this being the cause of my MB pump failures.

Thanks!
Andrew

964Andrew

Anyone knows what this butterfly type of gate on the input shaft is? I am suspecting this to be the reason for one sided pressure support loss. Maybe a pressure relieve valve activated too soon while turning the wheel?


(picture borrowed from KLA industries)

Thanks!
Andrew

964Andrew

Just received info from KLA industries. The circled element is called barrel valve and could be the issue. Finally I'm getting somewhere.

Thanks!
Andrew

964Andrew

If anyone can provide service instruction for the barrel valve in particular it would be awesomly appreciated.

Thanks!
Andrew