I've been working on my '79 for about 2 years now and have always had a problem with the break pedal being "spongy" with the engine running. With the motor off it starts spongy, but as I pump the pedal it stiffens up.

When I press on the pedal in the driver seat I always hear air blowing from around the rod that connects to the back of the power booster.

It became so hard to get the car to stop I decided to replace all the components in the brake system except the proportioning valve.

I ran all new brake lines and hoses to the front and rear.
I put a new power booster and master cylinder on (after bench bleeding).

Now I just got finished, bled the brakes and it still is the same! No evidence of leaking and I still hear that damn air sound.

Can someone please shed some light on this for me, it's driving me crazy!

Thanks

 

Well if you're hearing the "air sound" I'd wonder if your booster has the rubber boot on it to seal it around the rod and firewall?
When you say everything, did you replace/rebuild caliper pistons and wheel cylinders? Might also need to power bleed the system or vacuum bleed the system.

 

The power booster/master cylinder came with a new rubber seal and I installed it like the old one was. I'll attach some pictures of the rod to firewall area where the noise is coming from.

Would a leak in this location effect the brakes that severely?

I didn't change out the calipers/rods.. only new pads, bearings, rotors, etc.

Thanks

 

Let me guess....your car has cruise control? The air sound you hear just might be the vacuum cruise release switch leaking. It's under the dash, up near the brake light switch on the pedal assembly. You can bypass that switch, then see if the brakes work any better without having a vacuum leak.

 

Man if I have cruise control, its new to me. There are no switches or controls to indicate a cruise on/off.

The only wire/button I see involved with the brake pedal assembly is a switch that activates the brake lights.

Any ideas?

Thanks

 

Well it was a thought. I once had the same "air leaking power brake booster" that turned out actually being a bad cruise control vac switch. If your car had cruise, there would be a finger button switch in the very end of the turn signal lever.

 

nothing like that on the turn signal. I will check for leaks in the morning, but what the hell is that sound??

 

Are you sure it's an air leak, and not just the diaphram noise that's normal to a booster working? If you stick your head under the dash and operate the brake pedal you'll hear the booster working on almost all power assist brakes.
I'd put a vacuum gauge on the engine while it's running and see if you get a huge drop when you hit the brakes. If you have a large vacuum leak the engine rpm should actually increase when you hit the brakes also.

 

It would make sense to me that the diaphragm makes a sound when pushed and since I have to push the pedal all the way to the floor it makes the sound more evident.

So assuming that isn't the problem lets look at the 2 facts I know:

1.) The pedal can be pumped with the engine OFF and it will get firm after about 4 pumps.
2.) The pedal can be pumped with the engine ON and it never gets firm and always goes to the floor almost.

So from this, what would be the best thing to check?

Thanks

 

Check your brake pedal movement and adjust the push rod if necessary. If you have too much "free play" before the pedal arm actually starts pushing the rod against the booster/master cylinder, you may not be giving the master enough travel.