stace

in recent weeks I was getting a brake booster warning light when i started the car. after a few blocks the light would go out. during this time i would have no "power" brakes but the brakes worked with much more force. I ordered the 3 ABS relays that mount in the lower boot - passenger side thinking that would help.
that did not solve the problem. in addition the problem is no longer intermittent. the power does not return after a short distance and the warning light does not go out. I looked at the brake master cylinder (2) and proportioning unit (1) (in the attached photo). As this seems clearly electrical I checked the connections on the proportioning unit but they are clean and tight. any suggestions??? a search yielded very little on brake boosters. I realize the C4 system is different than the C2 system. car has 84k mi and the system was flushed a few months ago.
Thanks very much!

mpruden

I don't have a lot of experience with that system, but I did stumble across a thread with some great troubleshooting info. Hope this helps.

stace

that was a huge help! thanks very much! I thought that might be the issue but I couldn't find the pressure switch. now I know where to look... much appreciated!!!!

Stealth 993

1. in your photo is the ABS. The brake booster is the black balloon thing on the other side of the trunk.

It's totally normal operation to have the brake light on for the first 20sec-2min when the car is started. You can try to bleed the booster, there is a special procedure for it. I know it's in the Bentley book and factory manual.

JM993

I believe that's the pressure accumulator.

OP, if you determine that you need to replace parts, I have an accumulator and other C4 brake parts for sale in the parts for sale section:

https://rennlist.com/forums/showthre...ferrerid=21390


Cheers
Joe

stace

thanks to you both for the suggestions. yes the black sphere on the passenger side is the pressure accumulator - I have bled my brakes a couple of different times. air in the system would be give me a spongy pedal. I have the opposite problem. very firm pedal - no power assist. I do think the problem is electrical and the pressure switch sounds like the culprit based on the above linked thread. I will keep the parts in mind as I dig into this more this weekend. the brake booster is a big ticket item and JM993 your parts would be a big savings....

thanks again! Rennlist is a great place!

Stewart

I had brake booster pump failure (it's in the front of the trunk behind the rigid fold down carpet) - I'd started to notice the brake pressure warning light staying on for longer, and eventually intermittantly during normal driving, and I could hear the pump running much more than normal - it was clearly having to work hard to retain adequate brake pressure. It's an expensive part: £1200 here in the UK and can only be sourced from Porsche.

clubsport1

How is the condition of the cars battery?

I had a few brake warning lights stay on after the car wasn't used much, battery was weak.

I fitted a new battery and it has been perfect ever since.

May not be the issue, but an easy fix to tick off of the list.

stace

Battery is fairly new. And now even after driving for an hour (very carefully) the light is on and the brake is still not boosted at all. (Is that what driving a 356 is like?). Thanks for the thoughts - all comments welcome!!

mpruden

Just another thought. Have you checked your voltage at the battery while the car is running? Any reason to think your alternator could be failing - and therefore causing the low assist pressure and lights to illuminate?

stace

thanks MPruden and thanks Stewart!!!! turns out when I looked at the pump more forward and just behind the bumper one of the 2 electrical connections was loose! even with the retaining clip someone must not have seated the harness connections properly and it eventually worked loose. a bit of contact cleaner and snapped it back in place. works like it should. again thanks for all the suggestions! back on the road again!

mpruden

Awesome. That's my kind of repair. Nice job.