What would cause a master cylinder to spray fluid out of the cap? Car is a 67 ford, with a dual chamber master cylinder, and originally had manual 4 wheel drums. That master cylinder leaked out of the cap, and there were drops of fluid sprayed up on the underside of the hood, and the inner fenderwheel. It was always losing fluid to the rear brakes, with no other obvious undercar leaks. I had a garage install the SSBC power front disk conversion. This included a new MC, and added a rear adjustable proportioning valve at the rear of the car. Brakes were great for a few months, but eventually, I started losing fluid to the rear again. I noticed that I had spots on the hood and inner fender around the MC again. Bleeding them would make it fine for a month or less, then it would go back to leaking and losing fluid to the rear. So the current scorecard is two different MC's, different front brakes, about 75% of the brake lines replaced. No obvious leaks under the car, or on any brake lines. Brake lines are away from the exhaust. Spots of fluid on the underside of the hood, and the front of the MC (rear chamber) stays wet. Been like that with two different MC's and caps. Both caps and gaskets looked fine, no obvious flaws. Anyone have any ideas? This is driving me nuts. I'm about ready to have all the lines and splitter replaced, along with the MC! Thanks!
Do you have a 10# RPV in the master or in-line? If not, it could be drawing in air past the wheel cylinder cups. Here's a quote from ECIGUY from a topic yesterday...
MC has the bellows in the gasket, yes. Car was manual drum brakes, I had disc put on it that are basically the optional stock parts for that car, other than the booster. I was going to replace the MC, and I was told the disc-drum unit from 67-72 is the correct replacement part. It's my understanding that the MC will have the correct residual valve in the port for the rear line. Is that wrong? Car is pretty much using all factory stock parts, except for the vacuum booster. Once everything is bled, they work great for about 3 weeks, and then I start losing the fluid in the rear chamber again. It's a pretty erratic loss too, sometimes it's barely anything for weeks, and sometimes I have to add some ever few days. I don't know if there is a corrolation with hard stops or not, I can only assume.
To see if the RPV is in the M/C - you can disconnect the line and CAREFULLY poke a paper clip or similar device in there - should you feel resistance - it's likely to be the RPV - if you feel nothing - it's likely to have been elsewhere in the system. BTW some of the older cars didn't use the "conventional" m/c RPV's and instead used other means - for instance some used "LIP SPREADERS" (I forget if that's the correct term) that were thin washers mounted directly beneath the wheel cylinder rubbers. This was just another way to prevent the system from sucking air upon release. If you have those and your wheel cylinders are shot - may be the cause of your trouble. In any event - since near everything else has been replaced - it needs a lookie see back there anyways. I have also seen a RPV built INTO the "T" fitting for the rear brakes - seems they put those thing in quite a few locations over the years. I also have to wonder if the rear brakes are way out of adjustment????
I'll try that with the MC, and see if that is there. I was reading last night, and one article said that most MC's don't come with the RPV installed. I guess you're supposed to reuse the old one? The rear brakes are constantly out of adjustment. If i adjust them to where they are snug, with just a bit of drag, it either makes very little difference in braking, or they're too tight and drag enough that I can smell them getting hot just a bit. It's never consistent, and i've always tried to make sure they're just right. I've never had issues like this with rear brakes. I've considered biting the bullet and converting to rear disc also, just so I don't have to adjust them so often. An adjustment last for about a week before they're gone again. All hardware was replaced, and it didn't make much of a change. Adjusters currently look fine, not rounded off. Really starting to suspect that valve isn't there.
If the m/c is from a power brake Mustang 67-72 RPV for rear brakes is in the cylinder behind the outlet port seat. HemiRambler gave you good info. As for the out of adjustment rear brakes, those year Fords had a left and right self adjusters, if they are installed backwards you may be "un-adjusting" the rear brakes when you back up.
Sometimes when the fluid returns to the master cylinder, it squirts up pretty high. Check the seal around the cap, maybe it's just leaking. If the rear brakes are hot and dragging, the fluid can expand and push out around the cap. I've had that happen before too.
is the rod coming out of the booster that pushes on the master cyl piston adjusted right? I don't know the exact specs on this setup you have,but on most master cyls. that rod is pushed on by the pedal and then pushes on the piston inside the master. this is if you have a booster failure you still have manual brakes. if that rod isn't adjusted right the rear compensation ports in the master cyl are blocked possibly causing this problem.
The Jalopy Journal
