motionbroker

My differential control light has been going on for some time now even though occasionally the psd light comes on indicating the system is working.

When the car was up on the rack in the shop we bled the system with the bosch hammer and all seemed fine but it appears that there is fluid leaking from the slave cylinder on the side of the differential.

Has anyone had this problem before ? I looked through the posts and only saw a single reference to this particular failure.

The dealer is telling me that it will take one month to get this part and I am wondering if anyone has had any luck repairing it. Unfortunately it is hard to locate in the shop manuals and since the car is 500 miles away from where I am now I am not able to asess the likelihood of repairing it.

Any advice would be greatly appreciated.

Thanks
MB

derporsche928

Hello,
I'm assuming it's not leaking from the line fittings or the bleed nipple, so that only leaves the the cylinder seals themselves.... Did you remove the slave cylinder to confirm it's leaking? (I would think any leakage from the cylinder would go into the trans, and you'd only be able to verify cylinder seal failure by removing it....)
Are you sure it's brake fluid, and not trans fluid leaking?
If your cylinder is leaking, you should have a corresponding drop in your PSD reservoir level....
There is an o-ring seal (easily sourced) where the slave cylinder mounts to the trans, and if it's leaking around this seal, I think it's going to be trans fluid.....
If the cylinder itself is leaking or bypassing, then I'd bet it uses simple u-cup seals which should also be easily sourced from a hydraulic supply house. Of course, if the PSD system has been neglected, and there is water and the subsequent pitting in the cylinder, then it should be honed before you replace the seals.... And if it's deeply pitted, you'll (sadly) have to replace it.....

Best,

borland

Mine failed on my 90' S4 last year. Make sure you replace the bellows at the same time, as any contamination of the slave cylinder with gear oil will lead to it's failure.

928.332.775.09 Slave Cylinder, $274.14
928.332.051.02 Bellows, $24.70

Prices were Sunset Porsche, less shipping. Parts came from Germany, so it was about a month of putting up with a few drops and slow leak.

The square o-ring inside the cylinder is what failed on mine. The cylinder is easy to take apart. I looked at rebuilding it with a clutch slave cylinder kit, but the cylinder for the clutch slave is larger.

The bellows is not easy to remove. It's a press fit. I used a flat nose inverse spring clip spreader tool to remove mine. Similar to this Snap-on transmission snap ring pliers...

http://cgi.ebay.com/ebaymotors/SNAP-...QQcmdZViewItem

The new slave cylinder has a larger bleed screw, so it makes putting a box ended wrench on more difficult than before.

motionbroker

Thanks guys.

Much appreciated. For some reason there is not much in the service manual about this particular component.

Regards

RyanPerrella

yes PSD isnt mentioned much. Apparently though the Jim Moorehouse CD's have all the tech bulletins relating to the PSD and many many more things. But dont take my word for it, i still havent bought his set. I have the manuals on CD, but i got them from someone else. I just hate buying things twice, in this case I bought the set from the wrong person, but i still do need to get Jim's. Those that dont have these service bulletins and tech bulletins would be doing yourselves a big favor in getting this very complete set.

motionbroker

I actually do have the set from Jim but the psd section does not really deal with the output cylinder in much detail.

RyanPerrella

yes, ive never really head of problems with the slave cylinder myself. But I would love to hear more on your solution.

My psd is non active, hasnt been since ive owned the car, Thats something i need to get to now that most everything else is now in order.