Bad master cylinder???

[make-tracks]

I’m experiencing s strange problem with my brakes. I suspect the master cylinder is leaking internally, however I’d like outside opinions before replacing anything. Here are the specks 1997 Geo Tracker 4 door, 4x4, 1.6L 16 valve, 4 speed auto.
The breaks do not hold pressure not even when pumped. If I pump them I can raise the pressure just enough to shift it from park. I am not lousing brake fluid and the fluid level in the reservoir stays constant. So now for the odd part…. Whenever I pump the breaks while it’s running, it drops my RPM’s significantly, almost to the point of stalling. Is it possible it’s a vacuum problem rather than my master cylinder, or is the master cylinder drawing so much vacuum that it’s causing the low idle???

[fordem]

If, when you say the brakes are not holding pressure, you mean the pedal does not stop going down, then there is a leak - if the fluid level in the reservoir is not dropping, then the leak is internal to the master cylinder.

[xxx]

starting when. ?
the story, it was all pefect , daily driving when....
or
found the car in a barn , parked for 10 years... bla bla....

if it dont leak, on the ground or under drivers feet (look behind mc, see a leak?)
then it's a bad MC
or is full of air (bleed it)

easy huh?

[Bex]

Perhaps check the brake booster and vacuum line going to it for leaks, as well as bleeding the brakes. Big vacuum hose goes to brake booster....

[xxx]

the brake work with zero vacuum.
and with a hard pedal. his is not hard.

[Bex]

He is also talking about braking affecting his idle, no?

[aquanaut20]

Originally Posted by Bex

He is also talking about braking affecting his idle, no?

It may if he pumps the pedal, drawing vacuum down..... Philip

[xxx]

the stroke decreases but not the hard pedal at the end
test it off road. remove and block the vacuum line.
or off road. cut the ignition and while coasting test the brakes.
the brakes must work with no vacuum, or the car is a death trap.

it drops my RPM’s significantly, almost to the point of stalling

both, if the diaphram cracks, it can cause a hot motor to go lean (this leaks is an illegal leak and makes EFI go lean, and rpm drop ,but on a cold engine , faster idle)
block the diaphram and retest. or do the diaphram leak down test. (pass ./fail)
there is a check valve at the entrance tot he brake booster, that most be good too.. it holds a vacuum in the chamber , so if the engine dies
you get 1 or 2 hits with ASSISTED brakes.


id not drive any car with those symptoms. the rpm must not drop. explain all symptoms, good and bad, with engine and brakes for better answers.
see my whos on first text file below.

[xxx]

see how the booster works
see how the rod passes thru the whole MC system?
always fix the mechanical parts first then the booster last .

see the direct path in graphic 3 here.
brake overhaul

do not drive a car that , won't hold a hard pedal. or is spongy or pulling brakes.
there are 3 class leakage paths, 2 external and 1 internal.
the 2 external leak from lines or MC or slaves, in plane view, see em leak?
the MC can leak inside, and has bad seals. inside. with no external signs
if the external is leak free, and bled.
then the falling non hard pedal, is a bad MC.

[make-tracks]

The breaks do work to some degree just very poorly (Not safe to drive). when I pump the peddle when it's cold it causes it to increase in RPM's. when the engine is up to temp it causes it to drop RPM's almost to the point of stalling. the break is soft, goes all the way to the floor, it's very soft until I pump it. after I pump it i have break pressure for 1 to 2 seconds.