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After being on holiday for a few weeks, I come home and find that the car brake pedal on my (automatic tranmission with ABS brakes) car will no longer spring back up after depressing it. After doing a lot of reading, the problem would appear to be either with the brake booster or the master cylinder. Unfortunately, I can't really tell what might be the issue since I can't find any information that seems to match my specific conditions. There does not appear to be a return spring on the pedal that is missing.

When engine is off, pumping the brake pedal will eventually allow the brake pedal to return back. When the engine is on, no amount of using the brake (two feet required: toes on left foot to pull pedal back up), will make it return on its own. I have verified that the brakes still have excellent holding power. When the car is on and in drive or reverse, the brake still engages. I have not tried driving with it because I live in a high density urban setting.

Based on the above, I think the problem is somewhere in the brake booster or the booster hose. I'd like to diagnose it, but am not sure how. Pressing down on the brake is easy and doesnt feel any harder or softer than it used to be. However, starting the car with my foot on the brake pedal does not "pull" the brake pedal down an extra few inches.

Can I remove the booster hose from the engine side and blow or suck to test for a seal problem? I should only be able to suck air. If I can blow air, I know there is a seal problem. The brake booster hose is not a closed system, is it?

Is there a return spring in the brake booster that could have failed? Is it possible to diagnose this?

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2 Answers 2

I would first check the hose - it is rubber, and they do perish from the inside out. Disconnect it from the servo end, and see if you get good suction on it with the engine running.

While you're at it, visually check all the flexi hoses in the braking system for signs of bulging or wear - if any show such signs, replace them all.

The return spring is generally in the back of the master cylinder. If the M/C is working correctly, the brakes should, with the engine off, behave correctly, but be harder to push. If they don't, replace that first. Have you seen any signs of fluid loss? In particular, is the level dropping with no obvious leaks? Master Cylinders can leak into the servo, with the fluid then attacking the diaphragm inside...

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Thanks for your answer. The hoses are all fine and there is no fluid loss. Brake have good holding power without having to muscle them down. I think it may be a combination of problems all stemming within the brake booster. I will respond as soon as I find the root cause. –  logicalscope Apr 13 '12 at 17:17
up vote 1 down vote accepted

So as it turns out, my car -- a Saab 900NG -- did not appear to have a return spring built into the brake booster. There doesn't seem to have been any evidence of it though there does appear to be a small auxiliary spring built in to help apply the brakes (not disengage them). The shop merely added a return spring and everything seems fine. The brakes are not tough, the fluid is fine, the master cylinder was in excellent condition, the booster diaphragm was in one piece, and the hoses were all sound. The brake lines were also in good condition.

Chalk it up to another Saab-related mystery. I've had a few of those lately and it makes me want to never have another Saab ever again.

EDIT: It would appear that there may be a return spring on the pedal itself rather than the brake booster. I am continuing to investigate this.

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