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Digitalchaos
03-05-2005, 04:42 PM
Hello everyone.

While driving my car to warm it up for an oil change, I noticed a peculiar phenomenon. When I apply the brake pedal, the car experiences a vacuum loss. This is amplified if I apply the brake pedal repeatedly. Reading the boost gauge, it goes from about 22 " of hg to around 17.

Could this be a bad brake booster?

Thanks for reading!

J.D.
03-05-2005, 09:11 PM
Could be a leaking diaphragm in the booster. Lately have you noticed that you need to apply more effort when braking?
Do the stock 93+ SCs have ABS with a vacuum booster? The 89-92 models don't.

scbird1
03-05-2005, 09:28 PM
Here is how you check that valve. after running the car wait about 1 hour then go out and pull the hose and the valve from the booster. If you still have vaccume like a cork pop, its fine. If not just replace the valve at the end of the hose. If that still dose not fix it then you need a new booster.
Any problems brakeing now?

Digitalchaos
03-06-2005, 03:38 AM
Thank you for the useful information.

J.D., the brake pedal is, and has been for some time actually very soft. The master does not leak and I have troubleshooted this with other before, but haven't put much time into it. Yes, '89-'92 brakes use the Teves Mark II system, with hydralic accumulator. Later models switched to a master cylinder unit utilizing vacuum boost canister and an upgraded abs computer system; Teves Mark IV.

scbird1, the valve that you have mentioned is new to me. By chance have you any pics? Tomorrow is to be warmer than its been, so I will try this after driving home. I assume this is a one way check valve which allows air out, but not in...?

Thanks for helping..

scbird1
03-06-2005, 01:43 PM
Had to through all my car pics but found this one of my 94

Digitalchaos
03-06-2005, 10:16 PM
Had to through all my car pics but found this one of my 94

Thanks for the pics I'll take a look.. btw, very nice engine bay!

Treys92
03-06-2005, 11:32 PM
mwahahaha.......that is now my engine bay :D . But it is beatiful thanks to mark ;) .

-Trey

scbird1
03-07-2005, 01:38 AM
Im sure Trey is keeping that way or better with his new mods. ;)

Digitalchaos
03-09-2005, 02:52 AM
Here is how you check that valve. after running the car wait about 1 hour then go out and pull the hose and the valve from the booster. If you still have vaccume like a cork pop, its fine. If not just replace the valve at the end of the hose. If that still dose not fix it then you need a new booster.
Any problems brakeing now?

I pulled the valve from the booster, and there was significant vacuum. I left it unplugged and started the car, the brake pedal was very firm and the engine nearly died in idle from the disconnected hose.

I'm not sure why I lose vacuum when I step on the brakes, but I have to conclude the booster is fine.

However, I now notice the gray rubber boot inside the car on the stem connected to the brake pedal is wet with a clear substance.

racecougar
03-09-2005, 11:39 AM
However, I now notice the gray rubber boot inside the car on the stem connected to the brake pedal is wet with a clear substance.

That's a sign that you're master cylinder is leaking. I had the same problem on my XR7.

-Rod