Bad Master Cylinder???

Ok, so I finally put all my brakes together (11" drum conversion from R & P). I put them all up and I'm very excited to get them going ... I do the mechanical adjust so the drums are very close to the shoes ... and then I bleed all four.

THe problem: The rear tires lock up good. The fronts don't even move.

I bleed the lines again. Nothing for the front.

6 months ago I had bought a REBUILT master cylinder from Advance Auto for $20. I don't think the master cylinder is pushing fluid out of the fatherst reservoir (the one that does the front brakes). Did I get a bad master cylinder? When I bleed the front, very little fluid comes out. I can pump the brakes about 30 times, and still not empty the reservoir. I'm pretty sure the rod for the M.C. slides all the way down ... but may be I'm wrong ... and the problem isn't a bad MC but the length of the rod (although there doesn't seem to be a way to adjust this)

Has anyone else had this issue ... they buy an MC from Advance/Autozone and it's crap ... If that's the case, any suggestions at where to buy it? Herm?

Or any idea in general about this ... thanks ...

 

I just looked at Herm's web site ... i see he sells "conversion kits" ... I just want to buy the MC ... not the braket ... it looks pretty pricy ...

 

Yup ... Brand new
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When you bench bled the M/C, was there an approximately equal amount of fluid flowing from both the front and back ports?

 

One of the most common overlooked things is bleeding the M/C. This will cause you FITS for a very long time. Never get a good bleed of the brakes without bleeding M/C.

 

i did bench bleed it ... but may be I didn't do that good of a job ... it didn't look like there was much fluid being pushed out the front res. Is this a sign of a bad MC ... It's just hard for me to believe that it went bad after I bought it 5 months ago

 

On my dual master-cylinder, the small reservoir is for the rear wheel cylinders and the rear (big one) is for the front disk brakes.

 

I'm not sure it makes a difference with all drums.
http://www.earlycj5.com/forums/showthread.php?t=15271

Although it certainly wouldn't hurt to give it a try!

 

I have 11" drums all around, so I don't know if it make a difference which reservoir works the front. The other idea I had ... I have replaced almost every line in the front accept this one "t line" ... do you think that might be clogged? Preventing the fluid and air from flowing freely ... When I bench bleed the MC it looks like fluid from out of both ports, but when I put it on the jeep, almost no fluid comes out of the front cylinders when I'm pumping them ... I can't understand why

 

should I switch the ports around too? So the rear res. is what powers the front brakes ... (it's the other way around in the jeep right now) ... I don't know if that makes a difference

 

Undo the lines at the "T" and see how the fluid is running from the master to the "T". It should be a pretty good trickle. The "T" on my GMC to the fronts was plugged. Cleaned it out and all is well.

 

so now what I did is I switched the lines at the MC ... now, the res. farthest from the pedal does the back brakes and the res. closest does the front ... I actually got good fluid flow from each wheel cylinder. I bleed all of them ... but still a soft pedal. The only thing I can think of is ... after I bench bled and I was putting it back on the jeep, I accidentally hit the piston about a 1/4 of an inch and it made fluid come out of the ports ... does that mean it sucked back in air to the MC? Would this make a difference? I just don't know how careful I have to be with the MC and not letting air back in ... I was thinking of rigging some lines so I could just bench bleed it while it was on the jeep ...

Other than that ... is there are no leaks anywhere else, would I have to assume its a bad MC?

 

get your helper to pump up the brakes and bleed it at the MC. just crack the line enough for fluid to come out. if its all fluid then you have bleed it properly. and it may be as good as its gonna get. I have replaced the whole assembly on other vehicles(booster & MC) and it will feel just a touch off from what i think it should be, but will lock up all four tires. may just have to get use to it. if you can lock up all 4 i would say run it

 

so when I was underneath the jeep taking off the MC for the 15th time ... I noticed that when I had the brake hose off just on the front valve to the MC ... it was leaking fluid drip by drip (slowly, but enough to notice) out of the whole ... and it was def. coming from there, and not from the top of the MC ... if fluid is leaving out like that, does that mean it's a bad MC ... that fluid can get past the seals like that??

 

nope, just gravity doing its job

 

sounds like a clogged hose








Todd

 

Well ... It ended up being a bad master cylinder that I had bought from advance auto in November ... It was still under warranty ... So I could exchange it for free... It feels so nice to have a firm pedal ... Thanks guys for all the help...!!!

 

I got my MC from Carquest and it had Made in the USA stamped on it.








Todd