weird master cilinder problem

[gadget73]

are you losing fluid only when the bleeders are open, or does it lose fluid when they're shut as well? Do the brakes work OK?

[tjltd]

Hello, sorry for the late reply, wednesday i didn't make it to the yard but worked all day on the car, so far this is what i got and left me puzzled:

1.-Took the MC cap off, disconected the brake lines from the MC and installed the bench bleed kit. I know bench bleeding is done with the MC off the car, but sorry for my ignorance but does it make a diference? i wanted to save some time

2.-Started with help of a friend to pump the brakes an it did notice bubles coming out, but at the same time discovered why the MC is loosing fluid on the disk reservoir and the drum reservoir getting overfilled, while my friend pumped the brakes i saw brake fluid shooting out of the disk reservoir (like a fountain).

3.-I think i can left alone the Proportioning valve part, since i disconected the lines at the caliper and fluid came out, by this i can say the valve is not cloged or something like that.

The car brakes semi-ok, feels a little spongy but other from loosing the fluid it brakes ok, with all this said i think the MC could be bad, what do you think guys?

Thanks for reading guys, apreciate your comments and all your help.

[gadget73]

sounds like you got a bad MC and its leaking internally. All of them will squirt a bit of fluid if you pump them too fast with the cap off, but it shouldn't be fountain-like.

[1987cp]

3.-I think i can left alone the Proportioning valve part, since i disconected the lines at the caliper and fluid came out, by this i can say the valve is not cloged or something like that.

Not sure I'm following on that one ...

[Archangel]

sounds like you got a bad MC and its leaking internally. All of them will squirt a bit of fluid if you pump them too fast with the cap off, but it shouldn't be fountain-like.

It will be fountain-like, but from the drum side, not the one that feeds the discs. I agree with Thain, sounds like a m/c with an internal leak - I had one bad right out the box last weekend, it happens, especially with the remanufactured units.

[tjltd]

Not sure I'm following on that one ...

just got home from work, sorry for that, i meant that first i tought it could be a cloged prop. valve that could be returning de fluid up trough the cap, but since i disconected the lines and pump the pedal and fluid came out maybe that wasn't the problem.

Thanks for all your help guys, i apreciated very much, think i'm gona have to get another MC, probably Sunday will be yunkyard day.

[tjltd]

hi guys, went to the yunkyard yesterday, got me another MC just to make shure, installed it and tought the problem was solved until i started bleeding all the lines, i noticed the bulb or sensor located on the prop. valve started leaking fluid, what's the deal??, i checked and it was tight but was lossing fluid on the contact side where the small 2 wire harness conects, all of a suden it stoped leaking , is the prop valve gone?? or changing the bulb can solve the problem??

by the way, the MC from the yard is way better, doesn't spit fluid like the other one.

again i apreciate all your coments and help, sorry if this is getting boring

[gadget73]

sounds like the pressure switch in the prop valve is leaking. should be able to un-thread it and replace it. That switch kicks the brake warning light on if it detects a big difference in pressure front to back.

[87_crown_vic]

here is a stupid idea... look under the the dash as if you were looking at the brake switch. look at where brake booster comes through the firewall. having same issue right now with the Grand Marq we just got. filled the reservoir and was bleeding the front brakes... opened cap and rear reservoir was lower than originally was. i looked under the car to try to find a leak someplace and nothing. i needed to do the brake switch and when i looked with a light to see what i would need for the brake switch, i noticed brake fluid. I FOUND THE LEAK!!! it wasnt a brake line bad on the car but instead have a bigger headache. now have to replace brake booster AND brake switch.

[Archangel]

Jim, that fluid got in the booster from the master cylinder, it leaked down past the seals in the end of the primary piston - if it just happened the booster is generally salvageable, just make sure you drain it out good. In any case, you should replace the master cylinder as well.

[87_crown_vic]

i have a good Master cylinder and booster on the donor car i have. it has definately saved me money so far by doing the parts swaps instead of junkyard or parts store.

[Archangel]

Yeah, that's fine, as long as you have something known-good to put in place of the one that leaked out in the booster.

[gadget73]

just a friendly reminder, if you do buy a new booster, get a new master cylinder. Most places wont warranty a booster unless the MC is done at the same time. You can often get them as a set for less than buying each part separate.

[tjltd]

hi guys, i guess the pressure switch is not available from auto part stores right?, i looked on-line at kragen and some other sites and no luck!, guess i'll have to go again this weekend to the yard for some switches

[Archangel]

just find the correct solid plug and seal the damn thing off - it ain't like you need a light to tell you when you blow a line