I have a 76 F-250 4x4 with power brakes and dual piston calipers. I just replaced the master cylinder. The original master cylinder had the brake lines coming out of the right side towars the engine. The parts guy said that this was not the right one for my truck and he sold me a reman with the lines coming off the left side of the vehicle towards the drivers side. So I rerouted the lines hooked it up and bled the whole system. The brakes work and feel great except for one major problem. I'm loosing fluid out of the front reservoir (the smaller one) and it seems to be filling up the larger reservoir and over flowing all over the place when I take off the cap. I have no other leaks and I am positive the fluid is transferring from one reservoir to the other.

My question is do I have something crossed? Is this a bad reman master cylinder? Or something else....

Thank You for your help.

 

i have the same problem. I had bought a new master cylinder and the same thing happens. Heck i even get fluid leaking out the back.

 

The only crossover points are in the internal seals in the master cylinder or in the proportioning valve.

Fluid leaking out of the back of the MC? If you mean around the brake pushrod you have a bad unit.

 

Mine too,
Torque, My master cylinder leaks out the top seal on the front small reservoir. I bought the truck and drove it a while. I thought, man I shouldnt have to push the pedal to the floor and slowly come to a stop. I checked the fluid. The front was dry and the rear was full. I put fluid in the front. Drove the truck and about went through the windshield when I hit the brakes...LOL What gives, the seal is good on the cover. The lines are not leaking. Maybe a 10" C- Clamp will solve this problem...LOL

 

my mc leaks out the back of the lid and gasket. I tryed filing the mc down for a better fit but no luck. I have had this problem with 2 new mcs.

 

I'm getting the C-clamp. I'll have to do some mods on the hood..

 

Torque,

If I drive the truck for a day the front reservoir is empty and the rear is stuffed full with fluid all the way up inside the cap. When I remove the cap fluid spills all over the place. It seems fluid is transferring from one reservoir to the other. I have no other leaks that I know of.

Could this happen if I mixed up the lines coming out of the master cylinder? The old brake lines had some mickey mouse adapters. I connected them to the new mc with out any adapters and they will only fit one way so I figured it was right.

Could it be the cap seal or p-valve?

 

my master cylinder fluid goes from the front to back and leaks all over when the lid is taken off. But it leaks out the master cylinder with the lid on while driving.

 

So you guys just think its the seal in the cap?

 

i don't think its the seal. I don't know wtf it is.

 

Well I guess I'll try a new master cylinder today.....

 

I took my cap off. Cleaned it real good with wire brush. Took the seal off. Cleaned it with wire brush. Had alot of rust. Had the time so I tried something new. High temp copper sealent. Ran a thin bead on the seal thinking I'd get a better seal. Let it cure for 20 hours. Guess What? It didn't work. I'm still getting leak around the cap. Maybe its from the vent hole in the top? I wire brushed the whole assembley and painted it 1200 degree black. It still leaks, but man it looks cool. LOL

 

jevans has the new master cylinder worked. I have had the problem with 2 master cylinders already.

 

I did install a new master cylinder a few days ago and I thought it solved the problem. It is nice to have brakes again and its a 100% improvment from when I first started on this thing but fluid is still leaking into the rear reservoir and over flowing.

Today I looked at the p-valve and it does seems to have a small leak. I also noticed a rubber o-ring was haging out of the valve. So....now I will replace the p-valve after Christmas. If that does not work I'm going to rig up a gravity feed brake fluid tank on the roof and call it good!! lol..j/k

 

jevans, i see you have the same problem. Tell me how the proportion valve works. its about the only thing left.