Quote:If that's the case, would I still have manual brakes at the lower 1/3 of the pedal?

No,You would eventually lose all braking pressure as the more you push on the pedal, the worse the seal between the dual-action piston and the sleeve it travels in gets worse until you don't have any brakes at all and at this point the brake warning light should come on.

Explanation of system:
Think of it like pushing liquid inside a straw with a ram (say a pencil) the pencil (ie: the Master Cylinder Piston with 2 seals) fills the inside of the straw except for a very tiny area.

When you push on the liquid with the pencil (MC piston) the far end of the pencil is sealed right up tight with a cork (Brake calipers/wheel cylinders) and nothing leaks at that end but from the extreme pressure exerted by the pencil (there is so much pressure) .....and since there is a Tiny orifice located around the outside case of the pencil, the fluid squirts out past the pencil "Into your hand" ( the MC reservoir) which causes the pencil to go further in the straw (pedal goes to floor) , the fluid that comes out of the straw goes into and stays in your hand (the MC reservoir)

No leaks...no fluid loss....The piston in the MC just can't hold the pressure and leaks back.

 

Finally had a chance to work on this thing. Master cylinder did the trick.
Thanks a million, Mil1ion!

 

I'm having a similar problem. My brakes seem to work fine at first and then as I slow and the engine slows the pedal becomes hard to push and the brakes loose their power. (Feels like I'm on ice). I push on the pedal with the engine off and then start and the pedal settles another inch or so.

the engine is running rough at idle and sounds like a box of rice crispies. I have been searching for a vacuum leak.

I just replace the Master cylinder about 8 weeks ago.

 

I found the vacuum leak. It's between the booster and the Master cylinder. It looks like a small dent right at the bottom of the master cylinder, on the booster.

 

what happens if you shut off the engine.... pump the brake pedal until all the vacuum is gone....keeping your foot on the pedal in the brake applied position ...then starting the engine ?

What does the pedal do ?


Next test:

with the engine running press your foot on the pedal until all the vacuum is evacuated....keeping your foot on the pedal ...shut the engine off ...keep holding the pedal down for One minute......

What does the pedal do ? come up or go down or stay where it is ?

 

it settles a 1/2 an inch or so.

 

Well now that I plugged the leak. When I turn off the engine with the brake pedal pressed, it comes back up. The brakes seem to be working much better.


Thanks

 

for the second test ....If the pedal came up a little ...you have a vacuum leak somewhere.

Either the check valve,vacuum hose or booster is leaking.

 

Once, I have all the leaks plugged, should the pedal stay in the same place?

 

Return to test #1 in Post #20 and if the pedal drops a little when the engine is re-started the booster system is fine.

 

Thanks for your help.