Master Cylinder Leaking

[thedartsport]

I tried the search but didn't see something specific to my problem.

The car is a 1972 Swinger, it has 74 Sport front discs, and I recently swapped an 8.75 in. I took the backing plates off my 7.25 to reuse the brakes, but when I got everything back together, the car struggles to stop and the master cylinder leaks out of the cap and melted the paint on my inner fender. It didn't do this before, so I figured maybe I mixed the drums up when I put it back together. I adjusted the rears and it stops better but still takes a lot of effort and leaks. They're bled and all. What gives? The only thing I can think that's different is my parking brake isn't as tight and I need to snug it up, but I don't see that causing a difference.

Any help? Thanks!

 

[j par]

Honestly I didn't even read your whole post and I would say start with replacing the master cylinder. They're like $20

 

[rumblefish360]

Ideas it all and I’d do what J par said. It could just be a coincidence.

 

[j par]

And honest truth I think I might just put a new master cylinder fine soon as I'm putting my old one back on and I wasn't extremely happy with it. At that price I mean I can just have a clean new one to repaint.

 

[Jimacuda]

small bolt 7.25 backing plates on an 8.75?
Wrong offset for your application.
What axles, small bolt?
For stock you need small bolt 8.75 backing plates.

 

[thedartsport]

small bolt 7.25 backing plates on an 8.75?
Wrong offset for your application.
What axles, small bolt?
For stock you need small bolt 8.75 backing plates.

No it was a big bolt 7.25 from the same Dart the front discs came from. I bought Dr. Diff axles to replace the small bolt on the 8.75.

 

[thedartsport]

Honestly I didn't even read your whole post and I would say start with replacing the master cylinder. They're like $20

I would be more convinced that was the problem if it was leaking before. It's a reman I bought maybe 9 or 10 years ago, so I'll give it a try.

 

[j par]

I would be more convinced that was the problem if it was leaking before. It's a reman I bought maybe 9 or 10 years ago, so I'll give it a try.

So you are surprised that a remanufactured master cylinder that's 9 or 10 years old all of a sudden had a leak? You know like I tell everybody nothing's broken till it breaks?

 

[thedartsport]

So you are surprised that a remanufactured master cylinder that's 9 or 10 years old all of a sudden had a leak? You know like I tell everybody nothing's broken till it breaks?

Yes I am surprised. Worked just fine before the swap.

 

[Inertia]

If the brakes aren't bled correctly, any air trapped in either system, will act as a spring, and can violently squirt fluid back into the reservoir whenever the brake pedal is released, surpassing the lids ability to contain it. Lousy pedal may also indicate more bleeding is nec. cheers

 

[thedartsport]

If the brakes aren't bled correctly, any air trapped in either system, will act as a spring, and can violently squirt fluid back into the reservoir, surpassing the lids ability to contain it. Lousy pedal may also indicate more bleeding is nec. cheers

I bled them twice to make sure that wasn't the case. The pedal is firm as well but takes a lot of effort to stop.

 

[Jimacuda]

No it was a big bolt 7.25 from the same Dart the front discs came from. I bought Dr. Diff axles to replace the small bolt on the 8.75.

So you have 10" x 2-1/2" brakes on the rear now, same exact parts as before on a different rear you were using?
Just trying to be clear...
you were using a large bolt 7-1/4
swapped the brakes from the 7-1/4 to an 8-3/4
made no other changes to the brake system
pedal effort increased and stopping power decreased

Sounds like something maybe didnt fit back together right...
were the tops of the brake shoes fully seated against the top pin before being adjusted?

 

[mbaird]

Same thing happened to me... I just flat filed the MC down so the gasket would seal.. suck all the fluid out 1st then stuff resevoirs full of paper towel to prevent filings from getting into the system.