pumping brakes

[Frankensteinz2]

Hey guys,

I have been readin on line and talkin to msa. I recently restored my car and i am ready to drive it. However no brakes.

I filled the lines and bleed the master cylinder (which is pretty new), and at the wheels, farthest first. I can not seem to get any brake. I have to pump the brakes several times to get any kind of firmness, not even close to the old double pump action i use to deal with. Would I be right in assuming a leak some where? I see no fluid spurting out and the reservoirs stay up, but this is all that makes sense. I was thinkin a new master vac but i don't think i am having that problem.

Input please!

Thanks

Frankie

[jmortensen]

Do the master cylinder test. See if you can pump the brakes and get a pedal and then keep pushing hard and hold the pressure. If that works then try pumping again to get a pedal and then putting a very light pressure on the brake pedal. If it slowly sinks to the ground, then your master is bad.

If you stomp on the pedal and it goes down faster than it does with light pressure, then it's probably a leak in the system somewhere.

[Frankensteinz2]

i hear air comin out from around the master vac/ master cylinder area, but cannot locate it. Any likely places to look?

Frankie

[jmortensen]

If you hear air coming from the booster when you step on the brakes then it's likely that you have a hole in the diaphragm of the booster. That sounds like it is IN ADDITION to the bad master cylinder by your descriptions so far. Do the master cylinder test, ignore the booster for the moment. If the cylinder is bad replace it.

[Frankensteinz2]

Pedal sinks to the floor with decent pressure. Ordered a master cylinder already. We'll see where this put me. Probably gonna have to order the booster as well. Thanks for the help.

Frankie

[FastWoman]

When you hear the air sound, is it sort of a quick, asthmatic wheeze, or a prolonged hiss? If it's just a quick wheeze, then your booster might be OK with a functional and correctly adjusted master cylinder.

Another way of differentiating between a bad master cylinder and a leak is to mark the brake fluid levels and then work the brakes (i.e. with the pedal repeatedly sinking to the floor). If all of your fluid is still there, it's definitely the master cylinder.

[jmortensen]

Another way of differentiating between a bad master cylinder and a leak is to mark the brake fluid levels and then work the brakes (i.e. with the pedal repeatedly sinking to the floor). If all of your fluid is still there, it's definitely the master cylinder.

It is also possible to have leaks in between the cylinders where you pump the brakes and the fluid gets transferred from one reservoir to another, or also the rear seal could fail and pump the fluid into the booster.

[Oiluj]

Assuming your pedal goes all the way to the floor, when you push the pedal down, you will move the diaphram in the booster and force air through the check valve into the intake manifold. This will create the sound of air moving. (With the engine not running).

I'm having the exact same problem of the pedal travelling all the way to the floor. The booster is good, new master cylinder, etc.

I did some more research and now suspect that the brake switch valve may be the culprit.

If your system was empty of brake fluid, when you only partially fill the lines and press the brake pedal, the shuttle valve in the brake switch can move all the way to one end. This will prevent proper bleeding / fluid flow to the rear brakes and can cause the loss of pedal pressure.

I plan to check this on my car this weekend. Hopefully that will fix the problem.

[Frankensteinz2]

i think if this master cylinder doesn't fix the problem, im gonna just buy both the check valve and the brake booster together

if it still doesn't work then, im gonna crush the car, i kid i kid

one thing at a time, soon enough i'll have it stopin on a dime

Frankie

[Frankensteinz2]

alright i took off the master cylinder and its on the bench

I wanted to see how the plunger works from the booster, so i had someone press the brake while i watched the plunger move in and out

when the brake was depressed and the plunger moved forward, i felt a breeze of air as the plunger moved out, is this normal?? Or is it a result of a faulty booster?

Thanks frankie

[jmortensen]

Don't know but don't lose your reaction disk while you're messing with it.

[Oiluj]

The air coming out is normal, as it's pushing the diaphram.

As Jon hinted at, you probably just pushed the reaction disc out of place. Check to see that it is still in-place. If not, you have to fish it out or remove the booster and shake it out so you can re-install it. Don't ask me how I know this...