calio64

alright 3 master cylinders from auto zone and 1 from the dealer and still leaks from the back (were you bolt it to the brake booster) im really starting to get pissed, the reason im posting is because i just dont know what to do, hopefully somebody can point me in some kind of direction

thanx

Icemark

sounds like they are giving you a bad rebuild... try getting another from some other dealer.

calio64

i got another from another dealer today came home bolted it up and sure enough it is leaking from the back,WTF, why is this happening? is there anything else that can cause this like a clogged break line or something? i dont know what to do about this

WAYNE88N/A

Bad brake booster- the internal diaphragm is busted, allowing vac to "pull" the fluid from the master, past the rear seal. My guess...

calio64

brake booster? im thinking its gotta be something other than master cylinder cause damn ive gone threw 5 now and 2 from the dealer, are you sure that a bad break booster will cause a leak from the back of the master cylinder?

thanx

calio64

also do i gotta get a new master cylinder if i replace the brake booster

WAYNE88N/A

No, I'm not sure, I told you it was a guess

How does the brake pedal feel (before it went out)?

The FSM has several tests you can do to verify booster operation, have you tried those?

After the third master was installed and failed, that should have been the clue that something else was wrong. Bad part from stock- it happens. Four bad parts from different stocks- unheard of...

calio64

thanx checked the fsm, but didnt really find away to check the booster besides taking it apart, have you or anybody else seen a booster cause a leak from the back of the master cylinder, if so i will call a few junk yards to see if i can find 1, also is there a diffrence between the s4 & s5 n/a brake booster?

thanx again for the help

thanx

calio64

thanx checked the fsm, but didnt really find away to check the booster besides taking it apart, have you or anybody else seen a booster cause a leak from the back of the master cylinder, if so i will call a few junk yards to see if i can find 1, also is there a diffrence between the s4 & s5 n/a brake booster?

thanx again for the help

thanx

harley71105

I tend to agree with Ice and Wayne as possibilities...then again it sounds like Auto Zone stuff too...

pip

Wait is your brake booster leaking or is it your master cylinder?

rekx

when you are bleeding are you overextending the piston on the down pedal push?

RevinRx7

iTrader: (3)

Boom, This guys knows what your doing wrong. Are you bench bleeding any of these masters? If so how far you pushing? you shouldn't be pushing that hard to bleed them.

(I feel SOO John Madden right now cause of the "BOOM!")

OC_

you cant overextend the piston on the down push because it bottoms out

RevinRx7

iTrader: (3)

I love you....

calio64

i do bench bleed it before i install and yes i push the piston all the way in, is this causing the problem? it leaking from the back of the master cylinder were it bolts up to the booster, when i bench bleed it, it doesnt leak from the back but when i put it on the car it does, has any body heard of a bad brake booster to cause a leak?'

thanx

harley71105

Yo, could be that your original leaker filled up the booster cavity...maybe your master is NOT leaking...is the fluid level actually going down and does the brakes work OK?

calio64

yup the resovoir leaks and goes empty and the pedal just goes all the way do the floor, doesnt get stiffer as you push the pedal down

WAYNE88N/A

It's gonna go all the way to the floor until you've got it bled correctly. If you're not running the engine when you're trying to bleed, the booster theory may be null & void...However, you're still gonna have to remove the booster and clean up the internals, because if you have a bunch of fluid sloshing around in there, the diaphragm is gonna get at ate up anyway, if it's not bad yet.
Only other possibilty I can think of is that your proportioning valve is somehow shot, and that's causing your problems, but if it was me, I'd be zeroing in on the booster first...

BTW: You didn't do any "tweaking" on the peddle input rod at the booster, did ya?

rekx

yeah. and when you bottom out, you might be over extending the piston, then cracking the seals.

next time you bleed, put a block of wood under the brake pedal, and then you will know for sure that you arent over extending.