master cylinder cover gasket sucked in

[ScottG]

I'm having an issue with the master cylinder lid gasket. 2 of them have now sucked in and distorted the gasket to an unusable point. Fluid looks clean, and I don't see any leaks anywhere. Where do I start? Pedal also pulsates, not sure if that's related, but I'm sure it's the rotors.

[lolife99]

What are you working on?
They 67 C20 in your sgnature?

Have you done any recent work to your truck prior to this problem?

[ScottG]

It's that truck, but it looks like a later or aftermarket power brake set up.

[ScottG]

Haven't done anything related to this problem. Brakes are really touchy though. Don't have to press down very hard to lock them up.

[lolife99]

We need a little more info.
All stock drum brake set up?
Disc brake conversion?

Can you post some pics of the master cylinder?
Anything else you can tell us?

Touchy brakes could also be leaking wheel cylinders on drum brake applications.
Have you pulled the wheels off and inspected the brakes?

[ScottG]

Disc drum. Front discs from 83-87 3/4 ton. Stock rear drum Eaton rear end.
Looks like home-made hard lines all over the truck. Bad bends everywhere, but nothing kinked or broken.

[lolife99]

Disc brake Master Cylinder and Proportioning valve installed?
1/8"-1/4" "free play" in the brake pedal?

[ScottG]

Originally Posted by lolife99

Disc brake Master Cylinder and Proportioning valve installed?
1/8"-1/4" "free play" in the brake pedal?

Yes, and yes. Put a new gasket on it yesterday. We'll see what happens this time.

[Axle]

Sucked in the gasket off the edges so the lid does not seal? Bend the bails so it puts more pressure on the lid. The new gaskets, like everything else are probably not as thick as the originals.
If its a plastic master, theres plastic extension tabs that "lock" the gasket in place.

If its just drooping (sucked in some would call that as well) thats normal.

Alex.

[ScottG]

Actually, it.s the round centers of the gasket itself. It's like an accordion. I'm thinking I should get a new lid, even thought the lid looks newer, as does the master. Just checked it again, after cleaning it, and it appears to be leaking.

[oldspowered67C10]

Those "accordions" are there so that as the pads wear and the level of fluid in the master drops they can take up the space without letting out side air in. If youre finding that youre losing alot of fluid quickly then theres a leak somewhere, if you cant find any leaks on the outside remove the master from the booster to make sure its not leaking into the booster.