Re: Brake Booster Test, is it bad? - Saab 9-5 Bulletin Board - Saabnet.com
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Re: Brake Booster Test, is it bad?
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Posted by jeff02 [Email] (#2992) [Profile/Gallery] (more from jeff02) on Sun, 18 Nov 2012 14:29:04 Share Post by Email
In Reply to: Brake Booster Test, is it bad?, jeff02 [Profile/Gallery] , Sat, 17 Nov 2012 13:21:43
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Just tested the Bad car with a Good car. The good car once it starts the pedal is soft and quick to break. When shut off, the pedal becomes hard in about 1-2 secs and hard to break. All of this makes sense. Since the bad car has hard slow pedal all the time, either the booster is done and / or there is a problem with the vacuum flow. Since I changed the hoses from factory, maybe there is some very subtle vacuum flow going on. I am tempted to put in a 2nd electric pump just for the breaks.

Here is something that I have found about trouble shooting the booster (servo). I am in the process of getting some sort of air pressure gauge to test this out.

The one thing to note, I don't think that the pump runs with ignition on, only after starting engine (I think, will recheck).

------------------

This is for the Saab 95 (9-5) but will likely work on the 93 (9-3) as well.

Fault: Electric vacuum pump runs often and constantly flicks on and off.

Fix: The system has a slow vacuum leak, causing the low pressure switch on the firewall to trigger the pump relay too often.

Diagnosis: Fit vacuum guage to vacuum lines. System should hold vacuum. If not, Disconect booster vacuum line at booster, (pull it out of the rubbber seal carefully) and plug it. Then turn ignition on, pump should run, vacuum should increase to set pressure, (about 9-15 inches) and HOLD.

If it doesn't hold with the booster connected and does hold disconnected and blocked, you need a new booster.



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