Cheburator

The car is a 1990 MY 928 GT with various small improvements

I have the message "Clutch Control Off" every time I start the car. I also have the "Tyre Pressure Off" - but that is OK as I have the RDK brain off. My ABS works. Now the interesting stuff:

The minute I floor the gas the car would leave up to 40m of TWO black paralel tracks. The green PSD light on my dash comes on. I was at the Nurburgring again this weekend and the PSD light would come on in most corners, and I would also feel the action of the PSD. What is going on?

Also, can somebody post the schematics for the vacuum system on a 1990 GT. I had a look at John Pirtle's excellent site, but sadly the diagram is for AT equipped cars

Many thanks,

Alex

1990 928 GT (The Starship Enterprise)
1984 928 S2 5-spd (Frankenstein)
1989 VW Golf GTI 16v (Bugsy)

Randy V

Perhaps this video explaining PSD operation may be helpfull (courtesy 928 UK):

http://www.928.org.uk/mambo/content/view/135/59/

Click on the 'PSD Explained' link.

Takes awhile to load.

You may need to flush the PSD system. There's a great write-up by Tom Middleman (I think?) out there. Perhaps someone can post the link to it.

Vilhuer

Hi Alex, you can't stay away of from the Ring it seems. I'm hoping to get back there next May.

Try to change fluids first. http://928oc.org/journal/psd1.pdf

worf928

DYI PSD flushers should use the document from the 928 OC site (linked above by Erkka.)

John Speake and I did a comparative analysis of the OC procedure and the procedure available on the JM's CDs and we have come to the conclusion that the OC procedure is the safest and easiest to follow.

Randy V

Yep, that's the link - thanks Erkka. Credit for the procedure actually goes to Louis Ott and John Veninger.

worf928

Yup. And WallyP was the final technical signer-offer after he used the final procedure on his '90.

9x8

I'm getting the same "intermittent" PSD behavior with my '90 GT.
Most of the time it seems to work properly (light goes on, I leave 2 nice rubber marks), etc.

But when I burn rubber really hard (some 8-10 secs burnout ), it seems to deactivate with the "PSD abgeschaltet" error. After I shut down and restart the car, it seems to function until the next burnout.

PSD unit has been rebuilt a couple of years ago by PO, the fluid level seems to be proper. ABS/speedometer work properly too, so it's not caused by sensors, I guess.

Although I probably have an idea what might have caused this behavior:
The transmission is leaking from the top cover and I don't have time nor motivation to drop whole rear suspension to fix this minor leak at this moment, so I'm just topping it up for now. The oil I used for topping up was Castrol SAF-XO fully synthetic, it meets API GL-5 - but yesterday I noticed that its can says it's recommended by BMW for use in differentials w/o the limited slip.
So, the question is: can the 0.5 liter of non-lsd differential oil cause the PSD to not fully engage sometimes and lead to its deactivation by the ECU?
Should I replace all tranny oil with proper lsd oil now (and which one I should use?) or it won't cause any problems (aside from PSD deactivating sometimes) until I get to properly fixing that leak? I think I'll get to fixing it in a couple of months (or 1k to 2k kilometers).

Thanks in advance for all the input.

Herman K

Replace the PSD reservoir (it has a build in filter that may be clogged) flush and bleed the pressure reservoir and slave cylinder followed by exercising the transfer lock slave clinder with a hammer a like wise (after market) device

SteveG

For those following along, if you have read the OC instructions, you will know it is a work around to enable you to do this w/o the Hammer. I don't know how much the Hammer simplifies things, but it's not such a hard job w/o it once you figure out where everything is, fabricate a jumper to power the pump and realize you must access both wheel wells simultaneously.

You may also find yourself repairing the driver's side wheel liner. On RW, I have (finally) posted my pictures (under x- disintegration). It's not all that instructional, but it does show the wonders of roof flashing applied to this fix.

9x8

Like I mentioned earlier, PO rebuilt the PSD in 2006, and he seemed to do it properly.
That's why I'm blaming it on the type of gearbox oil or maybe sensors.

worf928

The basic mechanical bits of the rear end of the PSD are a non-limited-slip unit. It is correct to use normal 75w90 GL-5 gear oil.

I strongly suspect that the "issue" you observe after long burnouts is correct behavior. The PSD will shut off if it sees a large differential between rear wheel speeds and front wheel speeds. I suspect that an 8 second burnout is sufficient to convince the PSD/ABS ECU that something unexpected is happening. It only takes a few seconds on a Dyno for the PSD to pick up its marbles and go home when it sees that the front wheels are not turning and the rear wheels are turning with full lock-up.

Keep in mind that the entire purpose of the PSD is to eliminate rear wheel spin to maximize traction.


I did the editing of the OC procedure and was the first Beta tester. I've also used the Hammer. I think the OC procedure results in a more-complete flush of the system. But, the Hammer is quicker and is the only option if the rear wheel liner is disintegrating.

9x8

That's an interesting point, thanks.
Guess I should test it some more.

Schocki

The PSD will start to lock the rear wheels under hard straight line accelleration if a speed difference of 2 km/h or more is present between rear wheels. As soon as a speed of 30 km/h is reached the PSD will stop the action again.

If you go faster than 60 km/h and you are in a turn and the system notices decelleration, the system is actived to prevent oversteer.

worf928

When I've done burnouts in my '91 the axle hop can be sufficiently violent that it convinces me that it really isn't good for the drive line.

9x8

I guess it's my own fault that I made myself sound like the only thing I do is get out and burn some rubber.
In fact, I'm pretty conservative driver and usually resist that temptation, but sometimes you just can't control yourself - like when you are in the first row on the red light with a good empty road ahead. I'm pretty sure that every 928 owner understands me.

And it was that kind of burnout (as in, release clutch and accelerate while producing lots of tire smoke) that first produced the error, not the "hold the brakes and spin the wheels" kind.

Getting back on subject: what got me worried is that I get the error and have to restart the car to reactivate PSD - that surely doesn't look like normal operation. I guess I'll try to clean ABS sensors before looking into the PSD hydraulics.