DFitz

I just joined and am working on the brakes. 55 88 4-door Holiday.

I plan on getting a new master brake cylinder from Fusick, but had an interesting thought.

A black jelly-like gue came out of the master cylinder, and it was empty of brake fluid. Yes I had been driving it that way-scary.

Where the gue sat, corroded the interior of the bore. Years ago I bought a rebuild kit and hate for that to go to waste. I need an opinion on repairing the cylinder.

My thought was to repair it for a spare. I have filled the pits in the bore with JB weld, and have carefully sanded and re-surfaced the bore. The new piston seems to fit just fine, and the rubber seals seem ok as well.

My question is, do you think the JB weld would be affected by the brake fluid, or deteriorate with time? Would it work at all?

Again, this would be a spare. Getting a new assembly from Fusick to use.

Olds Scott

I am going to have mine machined for a stainless steel bore. One less problem with these old power brakes to deal with.

Olds Dad

I'd go new - I wouldn't trust that bore unless you have it sleeved, and that's probably not worth the effort for the price of a new.

Being only a single reservoir, that master is all you've got to stop that leviathan.

I'd consider a dual reservoir...I did it on my daily driver.

redoldsman

I would concur with Olds Dad. And there is no way you will reach down and pull the parking brake and stop one of these heavy all steel monsters. It is just not worth the chance.

DFitz

Agreed, and I will be using the new one. However, the question was, do you think JB Weld would work and not deteriorate over time for the spare? Really just waiting for the new one to arrive with nothing else to do.

Olds Dad

To be honest, I'm not a materials engineer, but I would not trust it - brake fluid is evil stuff.

redoldsman

You could soak it in carb cleaner and I and not sure it would still be clean enough for the JB Weld to adhere to. JB Weld is a great product. What the heck, you got nothing to lose. Put it in there and then use a hone on it. Let us know how it works. It might work as a space to get you home if needed. That is all I would use it for.

Tedd Thompson

I wouldn't try it on a bet, brake fluid is equal or better than paint remover and stopping is high on the list of things you want your car to do reliably.When could you use a spare that might fail ?....Tedd

DFitz

I'll be using the new Castrol synthetic brake fluid. Should be benign enough.

I was able to fill all the voids except 1. I have to reapply again to finish that one, didn't get enough JB weld into the crevasse. However, I did note an alarming manufacturing defect--enough to warrant not ever using the unit at all.

Along one part of the cylinder wall, right where one of the seals sits, is a radial occlusion, void of metal when the part was originally cast. I'm pretty sure this is why it leaked all the fluid out in the first place. So much for my idea. It is not a crack.

However, with that said, I was very careful in sanding the JB weld, and resurfacing of the bore. Still smooth, and round. The new piston seems to fit well, within .002-003" and the seals work ok. I may test it just to see if it works, but with the defect, it's now recycle material.

Thanks everyone for your inputs and ideas. Working on this thing is really a lesson in how far engineering has come since then, instead of guessing and saying, that looks about right!

I'd say failed experiment, but I still think the idea may be sound.