Spongy brake pedal

[TerryWalter]

Hi everyone,

The brake pedal in the car is really soft and spongy and seems like it moves to far towards the floor. So first I decided to bleeding brakes in order to flush out old fluid. That changed nothing, so nexted I replaced the M/C and bench bled it as per instructions (just replace M/C last week on 78 Lincoln). I installed the m/c and then bled each brake line as should be. After all is said and done the brake pedal still feels the same. The only thing I can think of is maybe I picked up a defective m/c from the store. Is there a way to check the m/c before I go this route? I thought of using vise grips and pinching off the hose to each brake and seeing if the pedal is harder. If so this should rule out the m/c but then what else could be causing the low soft pedal. What are your thoughts?

Thanks, Terry

[gmtech1]

What are you working on?

[TerryWalter]

Sorry about that,

1995 Park Ave base model.

[Tech II]

With ABS?

[gmtech1]

Have you pulled the drums and inspected the wheel cyl's for leaking, these are pretty bad for leaking on this car.

[TerryWalter]

Yes with ABS too.

[TerryWalter]

Thats the thing, there are no leaks in the system and the m/c has never gotten low at any point in the last 7 years that I have had the car. Just the pedal seems like it is soft and spongy even with the new m/c installed.

[gmtech1]

I'm assuming the car has alot of miles. The brake flex hoses may be weak and expanding under pressure, causing a soft and spongy pedal.

[TerryWalter]

I have check the rear brakes for leaks and the wear on the shoes and it all is in great shape, no problems there.

Well I exchanged the m/c for another new on and did the bleeding on both the m/c and the brakes. The pedal is still spongy so the next thing will be to replace the 4 rubber brake hoses I guess. Would there be anything else that could cause this? Could the vacumn assist be the cause of this? I don't think it could but I thought I would ask.

Thanks for all the help,
Terry

[Tony Silva]

You could pull the rear wheels off the car and manually adjust the rear brake shoes till they drag little bit on the drums as the drum spins.
I am thinking that maybe the rear self adjusters might not be self adjusting properly. It's just something to look into.

[Tony Silva]

Originally Posted by TerryWalter

I have check the rear brakes for leaks and the wear on the shoes and it all is in great shape, no problems there.

Maybe the rear shoes are in great shape because they are not properly adjusted???? ahha.

[TerryWalter]

Already did that when I pulled the drums off to look for leaks and the amount left on the brake shoes. The rear and front brakes are in great shape that is why I'm puzzled about the spongy pedal and figure it must be the rubber hose now because that is all that is left. Any other ideas that I might have missed. I try to be very through in everything I do but we all miss things once in a while.

[Tony Silva]

Man I'm stumped....could it be the residual pressure valve? Is the residual pressure valve built in with the new M/C or is it in a distribution block of some kind. Residual pressure valve is supposed to maintain some pressure in the front brake lines so that the caliper pistons don't "back-up" into the caliper piston bore. The ABS kinda adds another factor to the equasion. Do you see any fluid leaks near the abs distribution?

[TerryWalter]

No leaks what so ever. The brakes seems to work just fine never had a problem with them at all, just that the pedal seems to be spongy and needs to be pushed farther than normal as compared to our other cars (2003 Toyota Camry or 1978 Lincoln). I just thought that the m/c may have been going bad over time and letting fluid leak by the seals that is why I replaced it first.

[enslow]

Where are you getting your master cylinder from? This is something I would only trust from GM and not from anyone else. I hear of a number of people getting defective master cylinders from aftermarket sources. After that I can only think of some residual air in the lines (if you bleed too fast you can get air remaining), or those brake hoses as GMtech1 suggested.