Brake pedal is very soft: not air in system

[Zachary]

I’ve got a new-to-me 1991 Camaro RS. The car sat for 10 years in our driveway,so nobody actually knows what the pedal felt like.

When I got the car running it still had brake fluid in the resevoir,indicating no external leaks. Which would mean there shouldn’t be any air in it. The pedal was soft when the car was on,and I had to press it all the way to the floor to get even any kind of braking ability. I did a brake flush,and properly bled them making sure to not get air inside them. There was no braking improvement.

I’ve tried the backing up technique and parking brake technique to adjust the rear brakes. There was a VERY minuscule improvement,but nowhere near what it should be.

One question I’ve got is that when the car is off the pedal becomes very hard (which I know it’s supposed to.) If the master cylinder was bad and leaking internally,wouldn’t the pedal be soft,and easy to push when the car is off? I’d appreciate it if someone could confirm this or correct me if I’m wrong.

I wanna take the car in to get some other stuff fixed that’s outside of abilities,but I want to make sure I’m safe driving there. I don’t wanna pay for a tow either.

Topic

[Josh G]

Yes if you hold down the brakes with the car off the pedal should come to a stop and the master cylinder should hold it’s pressure.

I would start with a rear brake adjustment. If the rear brakes are not adjusted properly there will be too much travel in the brake pedal because you’re using up the volume of the master cylinder just to make the shoes contact the drum.

[Its me]

If the vacuum booster is working properly, the brakes should be soft when running, and after you shut the car off, you should have two or three easy pumps left. A bad vacuum booster would be hard all the time (running and not running). a bad check valve on the vacuum booster would have a soft pedal when running, but be immediately hard when the engine is stopped.

If The pedal feels right when the car is off (hard to push and holds) then when you start it and get vacuum assist and it goes very soft (and has far travel) it can very oftentimes be a Sticking Caliper pin. (THIS IS OFTEN MISDIAGNOSED AS A BAD MASTER CYLINDER)… Since the car has sat such a long time, this is very likely. Remove the calipers and see how the pin slides (or if it can be removed at all)… Another way to check is by observing the brake, have someone step on the brakes and if you see the caliper move (squeeze and then go back out after no pedal pressure is being applied), then you have a sticky caliper.

-Karl

[Author]

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