worf928

It's also on the OC site:
http://928oc.org/journal/psd1.pdf

John Veninger

For the street, I like the PSD.

It can be a bit strange on the track when you have big sticky tires and take the car to the edge.
The first year or two of DE with the GT, I had no issues with the PSD.

It it very hard to retro fit a non-PSD car with PSD, but easy to add an LSD unit to a PSD car (and cheaper).

steaditim

I just attempted to flush my system with absolutley no luck. The pumps starts and runs, but does not build pressure. I thought it might be an air lock, but I put a large syringe on the end of the feed line and tried to apply some pressure while the pump was running. I can force fluid through, but the pump wont do it.

SO. Any thoughts on how to deal with this? Is there anyone who rebuilds these PSD's? Anyone have one they're not using

Thanks,

Tim

Shark Attack

dude, look at the rear suspention of that car, spotless..... I think he is "one of those"

John Veninger

Tim,

Sounds like your pump has gone bad. Have you checked with 928intl for a used one?

TheoJ

Hey guys, when you have flushed the PSD, how do you test the PSD to see if it works without problems? How do you make sure you have a full lock when required? Let me guess: .......

That is when the tool (we) designed for flushing and testing comes in handy

Barry is right: the valve for the actuator should be pulsed, not just put 12v on it. I'm unsure if it will damage the valve, but is not designed for that.

regards,
Theo

Randy V

How should it be 'pulsed' for the flush?

Anything more specific - i.e. "Apply 12V to pump for 2 seconds, remove power, reapply power for 2 seconds, repeat pulsing for xx minutes or until fluid flushes out clean"...?

Rob Edwards

Randy-

FWIW, I applied 12V (continuously) for 3-4 seconds until the valve stopped pulsing (I assume because the accumulator pressure drops off to zero in that time- the valve at the differential makes a buzzing noise while the fluid is flowing, then goes silent as the flow stops), then re-charged the accumulator. I did a total of 3 bleeds of the actuator for the fluid to be clean, so the valve ran a total of 10-12 seconds or so.

Hope I didn't hurt anything.....

Okv

Completed the PSD flush today, using Jenniskens's Diagnostic unit.

Old fluid in accumulator did not look too bad, but what came out of the slave looked more like brake fluid suitable for a Volvo.

Then, the question:

Look at the picture.
The fluid at the bottom of the reservoir still looks dark?
Is this normal, meaning, it is the reservoir container that makes it look like there is some old fluid left at the bottom, or, did I not get all of the old fluid out?

Apart from this minor issue, I am very satisfied with the job.
Everything looks great, and it may even function well too, at least it did before..

Tails

Solenoid valve is a 12 volt electrical actuating valve which release high pressure brake fluid from the accumulator to the hydraulic actuating valve on the transaxle which locks up the differential (100%).

The operation of the PSD is a pulsed release, when it activates, applying a high pressure pulsed actuation of the PSD diff lock, however when the bleeding of the PSD system is undertaken does it require to be pulsed or just apply the 12 volts to open the solenoid valve bleeding hydraulic actuating cylinder?

This begs the question: Is the electric operated solenoid valve coil capable of taking 12 volts for a long period or can it only accept 12 volts pulsed?

If it can only accept a 12 volt EMF for a short period before the coil wiring overheats and burns out I would suggest that his is a bad design or is it capable of accepting 12 volts for a longer period without overheating and burning out, this is a better design?

In my opinion I believe the latter of the above two scenarios as I don't believe that an electric operated solenoid valve would be made that cannot accept the 12 volts for a long period of time than a 2 second pulse.

Opinion please or better still a definative answer, as to how the solenoid valve was designed.

If someone has a spare old PSD solenoid valve, a test could be carried out to measure the temperature rise over time of the coil when a fused 12 volts is applied to see whether it burns out and to measure how hot it will become.

If this is undertaken it will definatively answer the question of a pulsed bleed or a continuous bleed, subject to pressure in the accumulator and fluid level in the reservoir.

After purging the PSD, the only test that I undertake is to see whether the PSD pumps the accumulator up to pressure and automatically shuts off and then whether the light comes on when I make a sharp turn and get differential wheel spin or whether it activates on a wet surface when I apply power to the rear wheels again with a differential wheel spin. I have not experienced it actuating under excessive "Gs" whilst in a sharp bend at speed.

Tails 1990 928 S4 Auto

Kevin in Atlanta

I've done this twice using the afore mentioned instructions. The only thing that worried me is that the fluid level was low. No outward signs of leaks.

John Veninger

When bleeding you only activate the solenoid for several seconds. You don't even apply the 12v for 30 seconds. Why test to see when or if you can burn one out??

I know of no one that has damaged the solenoid using the flush procedure.

Marine Blue

This is number one on my list of things to do ASAP.

Anyone know if it's ok to use ATE Super Blue instead of the Castrol DOT4 which is suggested on 928OC?

Kevin in Atlanta

I used ATE Super Blue and Gold.

RyanPerrella

Doesn't the ATE fluid draw more water into the system? On brakes changed bi-annually that may not be a problem on a road car, but not sure if i would go with the ATE in the much less often flushed PSD unit.