donbayers

Well, I got about twenty miles on my new 63 repro master cylinder before I had a problem. I purchased and had installed this unit from CSSB.

All my brakes are binding up. Was able to get home by tapping on the MC with a wrench to get the piston to release.

I've done some searching on the CF and I see there could be some crap in the return hole?? Or there is something going on with the piston.

Anyone have any problems with these new units?

Suggestions about what to do??

Thanks for any help

66racer

Don If you have a full brake pedal, be sure & bleed the brake system good, you may need to shorten the rod some from brake pedal to M.C. Elmer

MikeM

If tapping on the MC causes the brakes to release, that sounds like the piston might be sticking in the bore.

You can look down in the reservoir bowl and see if the hole is open to the piston cavity to allow fluid to return. You can also check it for debris.

If the fluid can't return to the bowl when you release the brakes, the brake friction will heat the fluid, expand it and make the brakes come on tighter and tighter as you drive.

dplotkin

Indeed it will. Happened to me on a 62 Bonneville when I tried to get a higher pedal by adjusting the pedal push-rod and went too far.

If you fool around with adjusting the push-rod, be careful and check to make sure the brakes don't drag because as Mike says as you drive they heat up & clamp on harder and harder....

Dan

donbayers

Thanks for the reply so far. I don't think the rod is an issue as I have free play on the peddle before it actuates the rod. When I tap on MC and it releases then the peddle pushes down and you can feel it pressure up. ( hope that makes since).

With it stuck then the peddle travels through its free play with no resistance then is just rock hard with no further compression.

Other details. All new hoses last year ( rubber ones that connect to the drum). Replaced rear actuators inside drum last year. Fronts working fine.

Brake lines all in good working order. New MC was installed and bleed.

I was really curious if anyone else has installed one of these new units and if there was anyone having any issues.

If it is the piston that is binding up and no other obvious reason is apparent then what should I do or can do ???

MikeM

See post #3.

Look in the reservoir and see if the hole is open. If it isn't, you have a stuck piston or defective manufacturing. You can remove the MC and look at the back end and see if the piston is coming all the way back.

If it isn't, you could send the MC back where it came from. You could try honing the bore to smooth it up.

If the hole in the reservoir is clear and not blocked and the piston is all the way back in the bore, you have other problems. Until you confirm the MC is okay, you're just guessing. I assume you didn't have this problem until you changed the MC?

Kent in KC

Don - I've installed two of them with no problems so far. Can't really add anything to the suggestions the other folks have posted.

65 Pro Vette

I sent 2 back, one leaking in the car all over the new rugs, the other would not let the brakes release. Sent an original out and had it sleeved, works perfect.

boulderkid

PM sent.

donbayers

Ok. Was able to look at the MC. As you can see from the video the piston is moving. I also checked the return hole and that does not appear to be blocked by anything.

Ps. When probing the return hole with a fine wire it felt like I was pushing on something sponge-like, like rubber or something. Wasn't like I could push the wire down the hole unobstructed. No idea if that means anything.

Here is a strange thing. There seems to be a ton of peddle free play before the brake engages the MC?? I don't recall having near the peddle travel before the brakes engaged. What could have changed from the old (non-original ) MC that was replaced.

There is something still not right and the brakes as they don't seem to release 100% on a consistent basis.

Any ideas much appreciated.

donbayers

When you say you sent two back are to referring to two of these units I'm talking about or some other unit???

65 Pro Vette

I bought it online, It said Gm restoration part. I did get my money back. They are sold by a lot of suppliers on E Bay.

TCracingCA

So far i am not liking this Master Cylinder, but you are saying a whole bunch of free pedal and it still locks up. Is this happening at the very very end of the pedal movement when it locks? Are you getting the feel of engagement of the brakes and the peddle still moves? Have you watched each cylinder engage (would need to pull the drums) or block or hold the pedal at a couple of engagement points while seeing if a drum is locked or still turning? Can you tell if one drum is locking up early or instantly? But the others aren't or do finally, but after full engagement of the peddle? Etc.

MikeM

I can't see your video but I believe your problem is described in post #6.

Sounds like the piston isn't coming all the way back and when you probe the hole in the reservoir, sounds like you're hitting the piston cup because it's out of home position.

donbayers

OK, sorry about that. I was experimenting with upload from iPad.

I now have the video as public.

thanks for the comments.

Sure sounds like I could have a defective MC.

MikeM

Can't tell by the video if someone is stroking the pedal but if they are, there should be some bubbles or fluid spitting up out that hole while stroking the pedal.

So, I conclude your piston isn't coming all the way back.

JohnZ

That tells me your wire is pushing on the piston seal, which says the piston (and seal) are too far forward in the bore. The wire should go forward of the seal, and shouldn't touch anything except the bottom of the bore.

MikeM

Maybe the sixth time will be the charm?

donbayers

I think my best course of action is to send it back.

Zoomin

This is what Don's car is doing.



There is minimal back pressure on the pedal and then is goes solid, no feel of engagement at all. Have not observed each wheel cylinder, but when driving the car does not pull. If you let it go long enough, the car won't budge until you hit the MC and the piston finally moves back.