PSD pump question
 

Is there anything in the PSD system to cause the hydraulic fluid pump not to operate when energized, other than a pump malfunction? Just asking because I'm amazed at how many contingency safeties and shutoffs are built into these cars.
Also, is there a reason not to use silicon brake fluid after complete flushing, as it seems like brake fluid water absorption (over time) is the culprit in many of these PSD unit failures, and silicon brake fluid should help to eliminate the problem, as it's not inclined to absorb moisture.

Silicone fluid is not a very good idea.

As you say, it doesn't absorb moisture - but that doesn't mean that moisture won't enter the system. It does mean that any moisture that enters the system will slowly migrate to the lowest point in the system as tiny bubbles of water, resulting in rust pits.

Silicone fluid is also very susceptible to air entrainment. Tiny bubbles of air are almost impossible to remove, and make the fluid compressible, which is not a good thing.

The seals, hoses, etc. in the system are made to be compatible with glycol-based fluid, not silicone. Unknown risk.

Silicone and glycol-based fluids are not compatible. "Complete flushing" might not get all of the glycol traces out. Unknown risk.

Moisture absorption over time is best handled by flushing the fluid every few years. I use Castrol LMA (Low Moisture Absorption) fluid in mine.

Lex - Not sure how you're energizing, but if you're following the "PSD FLUID FLUSHING PROCEDURE by Louis Ott and John Veninger - 928 Owners Club" and connecting power directly to the hydraulic pump and it still doesn't cycle, it looks like your pump is toast.

Harald Stein is "the man" for repair. His website: http://www.stein-aviation.de/html/psd_engl.html

There is a fuse... Otherwise the relay should operate the pump and is designed to run until pressurized correctly - if it runs too long the system will fault out and stop. But on a restart it should try again.

Check the fuse - above the battery box - in the spare tire well behind the plastic cover - relay is here also (together as a unit).

Alan

^^^^

As suggested above, try running 12 volts and a ground directly to the pump.

The problem with most PSD pumps is that they never got serviced and the build-up of water/moisture over the years is what kills them.

Just a thought, but the ability for "normal" brake fluid to absorb a certain percentage of moisture might be a better thing than a fluid that will not absorb that moisture and "keeps" the water separated?

Keep in mind that the location of the reservoir is far from ideal.

The fuse was found blown and replaced with a good one. Hydraulic pump connecter was tested after the fuse was replaced and found to be powered. Connection to hydraulic pump produces no sound or evidence anything is happening. I was hoping for Porsche electrics to save me on this one, but I guess not. I'll take a closer look at the pump internals to see if I have any options left. BTW, what the hell was Porsche thinking when they decided on a material for the MY 90+ wheel well liners. My 87 S4 fender liners are still flexible and show no signs of fatigue, but these liners should be a case for the Grand Jury.

You have been following Jerry Feather's progress on this, right?

Are Jerry's finished yet?

Lex-when the tool arrives next week we'll have a looksie at the codes and follow the WSM procedure.

Michael

I'm sure Porsche had a perfectly good reason to make the later rear wheel well liners out of hardened candle wax...

Dan
'91 928GT S/C :eek: 475hp/460lb.ft

:roflmao: ... which they also used for the plenum cover and the in-tank pump rubber coupling.

I recall someone, perhaps in Jerrys thread, referring to them as "dried baby porridge" ... which I thought was equally amusing.

That's an understatement .... I love my cars, but I'd like a little one on one time with a few of their "engineers", to give them some percussive re-education.

I'm pretty sure that the PSD engineers had a bet with the Automatic Transmission engineers that they could make checking/changing the fluid harder.

They did.

You can walk up to any one of the vehicles with PSD and positively tell, with-in five seconds, if the PSD has ever had the fluid checked or changed.

I've always called them the $500.00 witness.....

And.....
 

We're still not sure which group won the bet....:grr::banghead:

They both did such a great job that it was declared a draw ... and they were promoted to work as a team on perfecting engine breathing and oiling.