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Master Cylinder Frustration

Is this a new MC, or rebuilt? Leak there should have shown when it was bench bleed.

Hate to say it, but needs to be pulled, for repair, or replacing...bad piston seal, bore, or both.
Bet ya already knew all that!
 
Is this a new MC, or rebuilt? Leak there should have shown when it was bench bleed.

Hate to say it, but needs to be pulled, for repair, or replacing...bad piston seal, bore, or both.
Bet ya already knew all that!
Yah! I knew that.....bench test was good and I worked the pedal several times prior to completing the whole system and it seemed to be fine. Rebuilt, nobody had a new one.
 
Rebuilt, nobody had a new one.
Just went back over the posts. Single pot, yeah, and rebuilt. Okay.

Might not want to fool with it, but if it was mine, I'd dig into it, to find out why it's leaking. Rebuilt stuff these days are a real crap shoot. If you can get a break-down diagram, to check for correct parts, and the order they go in. Usually pretty simple stuff, as long as the parts are in good shape.
Like the one you have, the only 'rebuilt' MC I tried, had been sand blasted. Didn't even think about it, until it fouled up my system.
Pulled it, looked it over...still had sand in it!
 
Just went back over the posts. Single pot, yeah, and rebuilt. Okay.

Might not want to fool with it, but if it was mine, I'd dig into it, to find out why it's leaking. Rebuilt stuff these days are a real crap shoot. If you can get a break-down diagram, to check for correct parts, and the order they go in. Usually pretty simple stuff, as long as the parts are in good shape.
Like the one you have, the only 'rebuilt' MC I tried, had been sand blasted. Didn't even think about it, until it fouled up my system.
Pulled it, looked it over...still had sand in it!
I'll remove it and take it apart, I have an old one here that I can use as a templet for the correct order.
I do have all the shop manuals and parts books from 59 -75, so The brake down should be in one of them.
Thanks for the help
Steve
 
Good luck on it!

The condition/size of the bore is the critical thing on MCs. Who knows...the bore in your old one, might be in better shape.
Probably like you...I hate doing things twice.
 
Good luck on it!

The condition/size of the bore is the critical thing on MCs. Who knows...the bore in your old one, might be in better shape.
Probably like you...I hate doing things twice.
Actually going to be the 3rd time.
Trying to get the car ready to sell, been tying up my garage space too long now.
 
Actually going to be the 3rd time.
Trying to get the car ready to sell, been tying up my garage space too long now.
Finally after 4 master cylinders .....2 new, and 2 rebuilts, same problem...I was able to successfully complete the replacement on one of my projects. I will say that after the 4th appeared not to be leaking after bench bleeding, I let it sit in the vise for 2 days... making sure of NO leaks! Then I installed it! I understand your Frustration!
 
Finally after 4 master cylinders .....2 new, and 2 rebuilts, same problem...I was able to successfully complete the replacement on one of my projects. I will say that after the 4th appeared not to be leaking after bench bleeding, I let it sit in the vise for 2 days... making sure of NO leaks! Then I installed it! I understand your Frustration!
Update........
Turns out that the MC may have not been bad.
Got the car up and running on a mini lift, It has power brakes with the engine running and going through the gears several times and applying the brakes the MC has not leaked.
I'll get it on the ground this week test drive and see if it holds true. Is there a symbol for fingers crossed?
 
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