Brake master cylinder upgrade

Hello all

I am having to replace my master cylinder for a second time in less then a year, is there a an upgraded master cylinder I can go with or am I stuck with the stock master, the car is a 72 that had drum stock and now has disc on all four corners

Thank you

 

Hey Kyle:
What went wrong with your Master Cylinder? Was is new or rebuilt? Do you recall what size the bore was? Smaller bore, easier pedal effort, but more travel, so pedal closer to floor. Larger bore, harder pedal effort, but less travel, so pedal is higher. Most aftermarket brake manufacturers, like SSBC recommend having at least 1" bore for 4 wheel disc brakes.
David

 

pedal will not maintain pressure, i went around and bled the brakes at least 6 or 7 times and there is no air in the lines. The master cylinder I bought was a remanufactered one

 

When you bled the brakes, where your bleeders at the highest point to make sure there is no trapped air pockets in the calipers? On my Right Stuff rear discs, you have to remove the upper caliper bolt and then pivot so the bleeder is facing upwards, otherwise air is trapped in the top portion of the caliper.........
You can purchase brand new 1" or 1 1/8" bore M/C's from any Mustang supply shops for pretty cheap.
I think this is the one I got from Scott Drake dealer, C7ZZ-2140-4WDB for 4 Wheel Disc Brake, can't remember how much I paid for though..........
David

 

So you're using a 72 master cylinder with 4-wheel disc brakes? If so, that's part of the problem right there.

 

I have never had good luck with a re manufactured MC. Get a new one if you can.

 

X2 on no luck with rebuilt units.

 

I've been having this problem also. I originally used the stock one on my car for the drum/drum and it worked good for two summers. When it went out I figured it was just old. I bought a brand new MC, not rebuilt, and it lasted me about two months. Pedal will go right to the floor on the first pump, then will build pressure after another pump or two. Still using the drum distribution block. I have the 94-03 mustang cobra brakes all the way around.

 

You guys running drum master cylinders with disc brakes realize they have a residual pressure valve that can cause your pads to rub the rotor, overheat and wear faster?

 

That is actually not true. Most residual valves were done away with in the early 70's. Mine does not have them. The actual real purpose of the residual valve was to keep pressure in the line when Master Cylinders were mounted down low. In that scenario they had issues keeping fluid in the lines. I've done a ton of research on this matter.

One thing I have learned though is the proportiioning valve is way different on a drum brake car. There is a meter in them to cut the pressure in half once it gets to around 200psi. Drum brakes are much more efficient and lock up so easily. At least for one stop anyways. Lol. So when I switched to discs, they require a lot more pressure. So I was fighting myself really. Not sure if it makes a huge difference or not, but I'm going to swap out the proportiioning valve and master cylinder and try again.

 

My 1976 disc/drum MC has one for the rear drums. If you look down inside the port with a flashlight you can see it.
The purpose of the residual pressure valve is to keep the lips of the rubber piston cup sealed against the walls of the wheel cylinder, fluid can't leak out and air can't be drawn in while the springs pull the brake shoes back. So unless the laws of physics changed in the 70's...
Disc brake calipers use o-rings that are larger and firmer instead of sealing cups so they don't need residual pressure.
MC's mounted lower than the wheel cylinders need higher pressure valves, I've seen them in the range of 7-10 psi. For systems with MC's above the wheel cylinders something in the area of 3 psi is all that's needed.

 

I have that set up and its working fine for me Ive got all wheel disk brakes and never changed the master cylinder
sounds like his master cylinder is bypassing

 

Hey Duane

Is this setup currently on your black car, I will be headin up there Saturday

 

YES thats whats currently on my black car

 

you guys going to bring MY white car for a visit? lol

 

I use a 74 manual brake master cylinder (new) with 4 wheel disc and the Ford Racing adjustable prop valve for the rear. I have the proportioning valve set at the baseline of 100 psi to the rear. On heavy braking, I can force a controlled lockup of rears slightly before the front. All in all the brakes are easy to stop the car and the pedal pressure necessary to lock it up is about as controllable as can be expected without ABS