65 brakes

[Guest]

I had a shop repair my brakes 3 yrs ago. I ordered and had them install a duel master cylinder for front disc and drum rears. About a year ago, the MC started pumping fluid over top of front reservoir. Replaced gasket, bail , and smoothed the top surface. no change. Replaced cracked plastic booster vacuum fitting and no more over topping. Now leaks from proportioning valve . Bought rebuild kit for that , have not installed it yet. Cant take it back to the shop,the people who worked on it have retired. My theory is that the P-valve was the culprit all along, at first jammed up and now broken and needs new rebuild and cleaning. The brakes seem to work ok. My question is ...With the new duel MC do I even need the P-valve?

[jopizz]

Yes, a prop valve is a must with front disc and rear drum brakes. It equalizes the pressure between the front and rear brakes. The master cylinder alone doesn't have the ability to do it.

John

[Guest]

I thought that just maybe the duel MC could develop two different pressures using graduated cylinder diameters or something like that???

[simplyconnected]

The M/C is a straight bore with two pistons, exactly the same size. Your combination prop valve is the common denominator that ties both front and rear systems together.

Originally, all fluid went to a block where each hydraulic line was connected. As each shoe stopped at the drum, that common block allowed more flow to go to the cylinders that needed more.

Now that your front and rear circuits are divorced, without the valve, the front pads would stop motion before the rear shoes because the fronts don't retract. This would cause the front to stop your car before the rear shoes get to the drums.

Your combination valve meters brake fluid to the rear first, then the front calipers come in, then the pressure proportions. I suggest you change your combination proportioning valve rather than rebuild it. - Dave

[Guest]

Thank you very much for the explanation. Do you have any suggestions on what type or brand proportioning valve would work best for this application?

[jhuebner]

Just purchased a dual chamber M/C for a Mustang to install on my 65 T Bird, and noticed that the diameter where the brakelines thread into are larger, has anyone had this situation I thought the brake line fittings would be the same diameter

[simplyconnected]

The factory did this to make sure nobody crossed brake lines. Look inside the ports. If they have cones at the bottom, you need, either an Inverted Flare Fitting adapter, or you can put a larger nut on the brake line.

If you don't have a 'cone' shape at the bottom of the hole, it is simply a common pipe thread.

All brake lines are the same size (3/16"). Even the new metric lines use the same size tubing, just the nuts changed. Back in the day, Ford used two IFF fittings, 3/8"-24 or 7/16"-24 nuts, both for 3/16" brake line. All the wheels, hoses and tees should be 3/8" IFF, but the combination proportioning valve and M/C had different sizes:


You can see from the picture that one M/C brake line has a 7/16" port and one output line has a 7/16" port. That way, the guy on the assembly line could not get it wrong. - Dave

[jhuebner]

Just ran the part # of the M/C I received, it is the one for drum brakes front/back........mail order sucks