Bill and I replaced the leaking power steering rack on my car with a rebuilt unit from ZF. My car is a '91 model with the lighter, higher pressure power steeering pump and airbags. According to the Service Information for '91, the rack has low friction seals. All I can say is that the car had significantly more power assist than older 928 models, which was a big reason for me to choose a '91 model.

Since the rack replacement, the car steers like an older model - much heavier than before. I do not like it at all!


There were a few unexpected hurdles we encountered during the replacement:

- When the new rack was centered, the wheels pointed slightly towards the right
- The shaft that comes out of the steering rack to connect to the steering column had its flat area in a totally different position than the original rack
- As a result of the above, it was very difficult to get the steering wheel straight. We had to reposition the airbag switch and steering wheel, then make slight adjustments to the tie rods (the steering wheel was "between two teeth")
- Before the rack replacement, I was able to pull my steering wheel towards me just a hint. In other words, it had a little forward/backward play. It does seem to have that now.

The old rack is gone, as it had to be returned as a core:

- On an attached plate it said: 7840955121 and 928.347.01026
- On the back of the gear housing (where the shaft to the steering column is) it said 7840.114EEEE - if I read this correctly.

Suspecting that I might have gotten the wrong rack, I did some research. This is what I came up with so far:

- The number on the ZF part I purchased is 7840-955-114W
- ZF literature says that racks for 84 and later models are interchangeable.
- Performance Products and Tweeks offer different racks for 928s up to '90 and for '91 to '95 models.
- Porsche PET also lists separate racks, but lists another one without any model year designation.
- A customer from England told me his GTS requires less effort since rack replacement.

Questions:

1. Is there anything we could have done wrong during installation that could cause the steering effort to be so noticeably higher?
2. Could the significantly higher effort be connected to the fact that I don't feel that back/forth play in the steering wheel anymore?
3. What is the difference in the racks for different model years, as offered by Tweeks and Performance Products? Is there a difference in the internal hydraulics, or is it just the low friction seals?

 

Hi Nicole,
I don't know anything about the different types of rack.

But, when you disconnected that nasty universal joint where the rack stub joins the main shaft, was the joint free in its movement ? Also, when you fitted it to the new rack, do you think it was fitted so that the universal joint was not "loaded up" - if you follow me.............

Maybe that could explain why you don't feel that slight fore and aft play at the sterring wheel.

There is a guy here in England who had his rack modified to reduce the steering effort required.

 

Nicole,

It sounds like something is binding & you may be heading for trouble.

I would lift the front tires off the ground, and check how much effort is required to turn the wheel with the engine off. It should feel about like you would expect with the wheels on the ground with the engine running.

Maybe check the front end alignment if it was disturbed during your repair?

 

(ignore this, I put in the wrong thread)

 

Nicole,

I had a DEVEK replacement 2 years ago and noticed the same thing. The new rack was definately more "stiff" turning the wheel. Now, either the rack loosened up or I just got used to the new feel. It doesn't bother me now.

 

Nicole. A word of caution. Is the heaviness of the turning at all uneven?

I had an experience with a rack that I personally rebuilt and it blew up the pump. Of course I rebuilt the pump myself as well, and that could have been the cause.

The supplier should be undterstanding if you situation.

 

This is also an issue. The rack main shaft CAN EASILY be put back into the main body in the wrong direction, such as 180 off. Maybe even some other random angle as well. This will then UN-align the fluid paths.*

*This is my understanding of the mechanicals from my expeirence in rebuilding a rack with another rennlister

 

If your steering wheel no longer has the fore and aft play that you were speaking of, it may be that the sleeve that fits onto the inner race of the steering shaft bearing has been forced into the inner diameter of the bearing race. If this is true, it would keep the steering wheel from moving aft when pulling on the wheel and may also be the cause of the harder to turn steering because it is binding the bearing. When replacing the rack you sometimes have to hammer the lower u joint off of the rack, which causes the sleeve to be forced into the inner race of the bearing. BTDT. new bearing and sleeve are about 30 bucks. It also sounds like previous front end work done on your car had been carried out without having the rack centered, or you have gotten a incorrectly assembled and/or incorrect model year replacement rack.

 

heh let some of your power steering fluid out and make it hard to steer, using lots of effort for about 2-3 weeks and then fill it back up with fluid and you will be amazed at how easy it is to turn. ask me how i know. lol

 

Joe:

If I was as physically strong as you, I probably wouldn't mind the increased steering effort either...

I chose a later model because the improved power assist was important to me (among other things). Since the 928 isn't a daily driver, I don't get enough of a workout from steering it and will probably always feel the difference (and be bothered by it). Besides, I like to keep the car as original as possible, and not downgrade it.

I have pretty much made up my mind to replace the ZF rack with an appropriate Porsche rack. All we need is to find a lift that we can rent or borrow for a half day. This is not a fun job to do on the garage floor...

Can't wait to have the beast feeling right again... Anybody have a lift available on a Saturday in the SF Bay Area?

 

The universal joint is a larger one that was closer to 8 mm on the old rack, and we set it the same way as it was, give or take a hint. I doubt it could make that much of a difference. But we will definitely take extra care of the joint when redoing the thing again.

 

No two parts are ever completely alike...

-I wonder if you might have the correct part...yet it simply hasn't been "broken in" yet. I changed the rack on my '85 earlier this year, and afterwards I could feel a definite difference: The car felt more like the S4 I test drove before I bought my current car- It suddenly had a certain "oily" smoothness. Not the same as my original rack at all. Of course, the little circular date code marks indicated it was from an '87 S4 originally....

How much harder to turn is it? I must confess to never having driven a GT or GTS. Is the steering effort much lower? If there is a large difference in your steering now, then something is definitely binding!

Best of luck!

N!

 

Nicole,
The part about the output shaft on your rack being different than your factory unit. My replacement had the same problem. I was not happy at that point,, I know your frustration.
Mine was 180 off, I riged it/made it work by unbolting the Ujoint shaft and flipping it 180. Not what I wanted to do on a part of that price.

Luckly I kept my old rack and would like to rebuild it some day. It's garage art at the moment, along with Rotors, rims, factory sport suspention, sway bars and mufflers.

I noticed the difference in feel also, all in all it was a bad day.

Larry

 

See my follow-up at https://rennlist.com/forums/showthre...652#post877652