My '65 has power disk brakes from a '71. I replaced the master cylinder and followed instructions to bench bleed it.

The first time, I plugged the outlets and couldn't get the air to stop. So I went to method two and used a bench bleeding kit. I ran tubes from the outlets back into the master cylinder which worked. Leaving the fluid in the MC and putting the top on it, I installed it on the truck, connected the brake lines and bled the system with my Mity Vac. The front pot on the MC which is for the rear brakes, still has air inside the MC when pushing the brake pedal. Even with the lid on which is extremely tight, fluid is forced out.

Anyone have some advice on similar experience? Before saying, NO, it's not too full.

HTF can I get the MC to stop leaking fluid?

 

Okay, so I figured I'd start over.

1. I disconnected the brakes lines.
2. Installed fittings with hoses that run into the MC
3. Bled all of the air out of the MC
4. Still, during the first 1/8" of the stroke, fluid squirts up from the little hole in the front pot and there isn't any air in the line.
5. WTF?

 

I finally got the front pot to stop squirting fluid. I disconnected the fitting and tube and quick attached the brake line and bled it. It is back to squirting fluid up. I'm at my wit's end with this already. I've installed dozens of master cylinders and done 100's of brake jobs and never had this problem.

 

That's kind of normal.

Not unusual to have the primary circuit cup resting behind the compensating port. So during initial apply the volume of fluid between the resting point of the cup and the trailing edge of the compensating port is pushed out of the port. Once the primary cup is past the CP and the chamber is sealed, no more fluid out the CP.

 

Thanks, that makes sense. But it is causing pressure in the MC making it leak.

 

I having a hard time understanding what you are trying to explain or ask here.

Air in the reservoir? Air in the drain line when your bleeding at the nipples? Air at the Mityvac?

Fluid leaking from where?

 

The MC and lines are connected and bled. The brakes work great. But fluid leaks out of the lid because of the pressure of the fluid that squirts up from the front reservoir. The lid is very tight but fluid still gets out. The level is about a quarter inch from the top.

 

Got it.

Does the cap have the rubber diaphragm to provide a sealed container?

 

Yes, exactly like that.

I bled the brakes again today using the old 2 person system. I think I finally got it to stop leaking. I have to get a few parts from NAPA tomorrow so I'm going to pick up another cover gasket just in case it starts leaking again.

 

The cap-diaphram-reservoir seal is supposed to be air and fluid tight, irrespective of anything going on with the hydraulics. All three need to be checked for any discrepancies not allowing a proper seal.