AO

If you have a 1990+ car, you have a PSD limited slip differential that uses pressurized brake fluid to actuate and engage the limited slip.

There's a great writeup on how to flush it on the 928 OC website.

Working on bigmac's car today and decided to flush the PSD fluid as the first order of business since after his supercharger install, he's gonna need it.

Here's the fluid out of the accumulator... Yuk! It should be almost clear.



And here's what came out the slave cylinder. Can you say milkshake? Yuk.

928 at last

That looks fresh compared to what came out of mine a couple years back.......should have at least 10 years left in it if it looks that good.......

I'm due to refresh again actually this year...

Leon Speed

Andrew, put the beer can down

Rob Edwards

Yep, always gnarly:

bigmac

Christ, Andrew PSA stands for Prostate Specific Antigen. Don't scare me like that.

bigmac

Boys, don't forget a PSA test @ age 60. I will help with the results if questionable..

the flyin' scotsman

how did you run the pump? I use Theos diag system that plugs into the brains

SeanR

Bosch KTS tool has the option for bleeding the PSD, seen a few that were locked up due to not changing it.

AO

Running of the pump is easy... turn the key to on, pump runs.

Actuating the solenoid is the tricky part. I have found that using my battery jump box works best. Hook the jump box up to the solenoid connector and then while you're under the car just turn on the jump box.

Solenoid gets energized, releases fluid, pump runs, more fluid comes out. Let it run until it's clear (I did stop a couple time to refill the reservoir) and then you're done.

Theo's tools is good for diagnosing, but not that convenient for bleeding IMHO.

Randy V

Isn't there some issue with difficulty in getting a wrench in there to remove something when accessing the accumulator?

bigmac

Andrew you are amazing. Thanks,Mac

Tails

A little difficult to get at the accumulator bleed valve, but a small ring and open ended ring spanner will do the trick. High pressure is the worry here.

The PSD should be bleed every 2 years and I do it at the same time as the brakes.

Bleeding the accumulator is relatively simple and the pump can be activated via the ignition switch, however when I bleed the slave cylinder, I activate the solenoid valve via an extension lead with an ON/OFF switch in line with the leads by plugging the the leads into the power socket for the pump so that I can actually be next to the slave cylinder opening and closing the bleed valve whilst ensuring that the reservoir does not run dry and suck in air (IIRC).

Tails 1990 928S4 Auto

blown 87

Now this is bad brake fluid.

GeorgeM

You guys forgot about the hardest part... getting the left rear wheel well liner off w/o it falling apart.

I thought mine were in good shape until I started taking it out. It virtually started falling apart in my hands.

How's that repro project coming... was that Jerry Feather doing that?

I guess I'll just patch with duct tape until a better solution comes along. Ideas?

AO

You're right. Fortunately for me this was on a 1990 (not my car) so there was no full liner.