Master cylinder leaking on bench bleed?

[Malicious]

Hi all another quick question. Just bench bleeding my new master cylinder and I've noticed I'm loosing a drop of brake fluid when the piston 'input' fully extends back out after being depressed.

I'm worried this means it's junk.

Some extra info: fully extended or returned the piston extends out past the mounting surface of the master cylinder by roughly .075".

The piston doesn't fully extend back on its own. It stops maybe .2" short. With very very little effort I can slip my little finger in and encourage it out.

I have a new bendix booster and it looks like the plunger extends out about .94" where the hole in the mc piston is maybe .86" deep, so I'm thinking the piston won't extend to the point that the drop occurs?

Appreciate any help!

 

[miller]

Malicious...is the master actually 'new', or rebuilt?

But considering these days, and where things come from, might bust it down to check it. (That's if your so inclined.)
Yeah, it should have full travel to the stop (clip) on it's own, unless it's hanging up somehow.
Don't know how the parts deal is, where your at, or take it back, and get another.

First one I bought was rebuilt...done badly...with the internal clip even the wrong size!!

 

[Malicious]

I'm in Australia so shipping back to the states really isn't an option. Would cost more then buying a new one.

I can't remember if it was new or rebuilt, but I think its probably fair to say its a rebuild. I brought it with a new bendix booster from Pirate Jack.

How hard is it to tear it down?

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To be honest, I'm getting pretty shitted off with all the new/rebuilt parts that just don't work. WTF happened to quality control??

I brought a rebuilt power steering box from A1cardone as insurance, and the input spline is completely wrong and it looked like it was painted with tar by a 2 year old using a mop. Fkn disgrace that this crap actually gets sold.

 

[Rocketman]

mine has been leaking through the winter and I did not catch it. It has already wrinkled the paint on the fender. It is leaking where the lines go in and at the bottom. I ordered one from NAPA, still waiting for it to get in.

 

[garrett1308]

The one on my roadrunner was fine, but it took two or three tries to get a good one for my trans am, but then again, almost everything has taken two or three tries to get a working part. You'll just have to keep trying I guess, :/

 

[miller]

How hard is it to tear it down?

Completely understand, Malicious.

Master is fairly easy to bust down. Of course, it needs to be off the car, and in your hands. Don't know which one you have, but all pretty much go together the same way. Bottom line is...if it's leaking...somethings wrong. If it's possible, get an overhaul kit for it. That will have the cups, seals, maybe even pistons in it, and a diagram of how it's goes together.

If the master is off, look at the mounting flange, and you should see a internal C clip just inside the bore. That clip holds everything in place. Simply take it out. Watch carefully the order the parts come out! I usually (and gently) use a air nozzle at the line ports, to 'blow' the parts out of the bore.
Going back together is just reverse, with all in good shape, right parts right order, with the C clip holding it all in.

The 'overhauled' master I had, the clip was too big, and the moron forced it into place. the master was also contaminated with sand-blast! Yeah, when I figured things out, that master went into the trash can. Bought a real new one from Nappy (Napa).
Should be able to find info on your master, and go from there. Good luck!

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Probably should add that, depending on the particular application, there's dozens of different types of masters out there. On that, the way they bust down, is just general, just minor differences.

 

[miller]

Just one example...

 

[Malicious]

So the master I have seems to have come from a 70+ model so I've found a 70+ manual with a break down. Looks pretty similar. Anyhow got it apart and the rear piston (to the rear breaks, called the front piston in the FSM) took a bit of air and players near the end to bring it out. Not a lot of force, but certainly didn't pop out like the front break piston. So bhind that rear break piston was a bunch of what I think is white grease. The FSM doesn't mention grease at all. It says only line with break fluid, so could this be part of the problem? I'm going to whip it off and reassemble. Thoughts?

 

[mopar12372]

in your situation i would remove grease , check seals fro cracks tears damage ect . if looks ok coat with brake fluid put back together and bench bleed to see if it leaks . what do you have to lose ?

 

[miller]

Dang, Malicious...we havin' fun, yet??? Heh.

Yeah, could be the grease. There should only be brake fluid in the master. Clean all the parts. Probably best if you inspect everything real good...burrs on any of the hard parts, nicks on any of the rubber parts. Make sure all the grease is cleaned out of all the ports in the master's body, with a look at the bore surface in the body. If it's scored...slight problem.

If it all looks good, simply lube all the parts with clean brake fluid, and go back together with it. But, I'll add if any parts look flaky, question it. A bad/wrong part put in is just a waste of time. Use your diagram to go by. Do it right...once...and it'll go.

 

[Malicious]

I actually went ahead and did just that, cleaned off the grease reassembled. No good spring back, still sucked and it still leaked. All the seals look good. They flare enough that they took a bit of pressuation to get them in. So it's go me beat as to why it's dicky. I'm wondering if the inner seals are too good and slow the spring back long enough to allow to much fluid to get into the bore and give me that one drop.

Anyhow, I have another master but the ports are wrong in it, so I checked that. Good spring back. So I pulled it apart and put the guts in the original master with the correct ports. Spring back was good, bench bleed, bam - working master! Happy man.

So I've chucked it in the car, with some fun of tightening up lines after the fluid was in! Just need to bleed it tomorrow night and it's good.

Thanks for the help guys, yet again this site is a gold mine!