I took my car for its MOT (road safety test) and it failed on a few items. The one I'm having a problem with is:

"Nearside rear Fluid suspension unit interconnecting pipe corroded and seriously weakened"

There is no fluid suspension unit and he has misidentified the PSD. Would a failing PSD line be a safety issue? I'm thinking it is so rather than argue that the car shouldn't have failed I'm looking to fix it and get it retested.

So to fix that I think I would need parts 928 315 095 02 and 944 355 081 01. Would I also need to bleed the system after they are swapped? Also the top of the pipe looks hard to access any tips?

Cheers,
Mike

 

Also I notice that the PSD system is only on late cars. Would there be the possibility of temporarily disabling the system effectively making it a non PSD car? I'm on a bit of a time constraint as I was supposed to head off camping today but may need to delay for a few days. If the system could be safely disabled so it wasn't going to fail while driving would that be an option? I'm don't drive it too hard so how often does the PSD actually kick in and how much more dangerous is a non PSD car? I don't want to try anything dangerous, I'm just trying to get my options straight.

 

IS the PSD warning light lit on the dash ? How did the MOT tester see the PSD ? It's usually hidden by the wheelarch cover isn't it ?

 

No PSD warning light. The cover from the PSD is missing. The MOT tester thought that the PSD was a hydraulic suspension issue. As there were some other fails on the car that I needed to fix I never argued the issue with him.

Also note the black line on the right hand side of the first pic isn't even connected to anything. Any idea what this is?

 

Spray the rusted parts with liquid grease aerosol, buy the correct cover so you don't encourage even more rust. Go to another MOT test center...

 

Ok. Sounds like a plan. I knew the cover was missing and plan to replace it. As for the MOT tester I think it is just a genuine mistake on his part. I have had my 944 done there a couple of times and he has been pretty reasonable in the past. I think I'll print out some PSD related docs to show him and see what he says. I'll take a look at the whole PSD thing a bit more closely when I have more time. I don't think I drive hard enough to ever engage the thing.

 

Just to make your day and cheer you up for your holiday, can I share my PSD crisis.

To start with, you can't find the wheel arch covers any more in the UK. I had to have one made up for me.

If you think radiator prices are unreasonable, wait till you see what you have to spend to recondition a PSD. I gave up in the end and bought a second hand one that seems to be ok.

The one consolation was apparently if the PSD is defective, it reverts to operating as a regular diff, so you shouldn't fail your MOT. It's not a safety issue.

Mine told me on the dash that it had been disengaged. I'm surprised you haven't seen the warning.

 

Hi Mike,

A failing PSD-unit is not a safety issue by itself, however depending how exactly it is failing can then actually also disable the ABS functionality on the car.

The black line on the right hand side of the first pic is suppose to be like that: it is the vent line from the filling/overflow plastic reservoir. Note also that the plastic reservoir has a build in filter that is unfortunately non-serviceable, which is another reason among several for regularly (every 2 to 3 years) flushing the PSD-unit.

Anyway: all you ever want to know about the PSD-unit, including who to send it to in Europe so to get a tip-top repair or replacement with two (2) year warranty, you can read from this thread:
https://rennlist.com/forums/928-foru...procedure.html

 

I would definitely send that unit away to get rebuilt/replaced. Follow all the additional advice and you'll have a better car and pass MOT (assuming you fix the other issues!)

 

If the fail was due only to the corroded steel lines, keep in mind that those are standard brake lines. Give them some time with some penetrating fluid to loosen the grip of corrosion, and replace in kind with new. A lot of the 'failure' symptom is visual, so some cleanup of the unit with some degreaser, followed by some work with a metal brush to knock down the obvious corrosion, might be what you need. Replace the soft hoses too, and flush after they are all replaced, and it will look spiffy again. If you manage to uncover a label that says "Porsche Spier Differential" (might need some spelling help) it might unclog the MOT tester's understanding of the pump function.

 

Regardless if you MOT guy is right or wrong about it being a safety issue (wrong, BTW), he did you a favor to point this unit out.

I believe a 1990 wheel arch cover is still available and will cover that pump, quite nicely. Roger, at 928 R US will know.

Whatever you need to do to protect that pump and the components is worth the time. There's a few of the 928 pieces that are going to be worth their weight in cocaine....and this is one of them.

Get that old fluid out of the unit, try to clean the old filter in the bottom of the reservoir (reservoir with filter is NLA), and bleed the system, as soon as you get a free moment. The unit is very low on fluid, BTW.

 

Greg, is there some sort of alternative reservoir that we can use? I am just thinking out loud, about a regular power steering fluid reservoir with some sort of in-line filter.

 

Pretty easy to add an inline filter to the supply hose - cut, insert and clamp.

 

I just used up the last of the PSD reservoirs I had, in stock.

It would certainly be easy enough to rip out the old filter out of the reservoir.

Does anyone know what kind of filter works with/is needed for brake fluid?

Micron rating?

Seems like the most common inline filter (fuel) might be too "fine" for brake fluid.

 

I tried getting the filter out but it seems bigger then the orifice in the filler neck - but what do I know 8>).
I concluded that you need to split the reservoir to get the filter out.