[frog3]

Greetings all!

I just updated to disc brakes using an appropriate kit and a new master cylinder for a 1979. After installation I have driven the car and found that the front brakes will gradually clamp down, forcing me to burn more gas to maintain speed, and the pedal will get hard. I can loosen the line for the front brakes at the master cylinder to relieve the fluid pressure and everything will work for a few more miles. The brake pushrod with the new master cylinder is too long, but I couldn't get the old one out of the old master cylinder, so the new one had to be pushed in slightly to meet the brake pedal.

I've ordered an adjustable brake pushrod to relieve that issue. My question to the members here is whether the brake pushrod is the issue or is it something else such as a clogged line?

Before anyone starts talking about boosters and vacuum, you should know that the vehicle has manual brakes.

Thanks for your input!

[MIL1ION]

Did you swap in the disc Proportioning valve as well ?

[frog3]

No proportioning valve at this time. From what I understand, that is to adjust the bias between the front and rear brakes. I figured I would have to do some testing first to see if I even need it.

[MIL1ION]

The way Ford brakes work via the correct PPV is the Rears come on first ......then the fronts take over the main braking.

These valves are that important and are required on Disc Brake cars

C5ZZ-2B091-B

[frog3]

I will add one as soon as I can. Do they go between the master cylinder and the front brakes or master cylinder and rear brakes? Though I realize the importance of the valve, I question whether missing the valve would cause the issue with my front brakes locking up and the hard pedal. I'm thinking that if the valve goes between the master cylinder and the front brakes in order to restrict the flow of brake fluid, it is hypothetically possible that there is too much fluid going to the front brakes. Why though do the brakes clamp and pedal get hard despite not depressing the pedal?

[MIL1ION]

You never mentioned having a metering valve either
Hope this helps.

http://econtent.autozone.com:24991/z...528007ee38.gif

[frog3]

Thanks for the diagram. I just found this page as well. It has a good explanation of the types and uses of valves in braking. Brake Valves: Operation and Service

So I understand the need to "hold off" the front brakes and the need to prevent rear wheel lock-up during panic braking. Do you have any thoughts though about why the front brakes are engaging gradually without depressing the pedal?

[Dieselman]

The brake pushrod with the new master cylinder is too long, but I couldn't get the old one out of the old master cylinder, so the new one had to be pushed in slightly to meet the brake pedal.

I believe this is the issue causing your brakes to grab slowly and have a hard brake pedal.
The following is something I would only do in an area where no-one is around, so you don't have to stop quickly.
Just a thought........hold the brake pedal up with your left foot will driving to see if this helps.

As stated above,proportion and metering valves are required.

INMHO, brake systems should NOT be pieced together. Braking systems are the MOST important part of any car.........for your safety AND ours.

Good luck

[dne']

I understand your question regarding ~ your front brakes eventually lock up with use.
Be specific: The front disc setup is what kind of kit? Granada, etc., and let me understand, the master cylinder is from a '79? I don't know if the master cylinder would be your culprit or not since the years are so far apart. And you say the rod is too long going into the mc? did you upgrade to a power booster as well? I would certainly think that if the rod was too long, and is actually staying pushed in a bit, pretty much all the time, could act as a one way valve, and "could" the brakes engaged. However, seems like the fronts would lock up much sooner than later.

FWIW~However, other something you may check, did you adjust the wheel bearing correctly? tighten till bearing is seated, then back off then retighten approx~1/2" turn? You shouldn't be able to take the rotor and feel any slop. Disc brakes require a tiny bit play in the wheel bearing to push the brake pads back after braking. That doesn't mean back off to where the discs are flopping around!

And BTW~ welcome!
dne'

[frog3]

The kit was from Summit, and ultimately supplied by SSBC. It's a bolt on so no Granada spindles. I didn't add a booster. From what I researched, the master cylinder should be fine. It has a 7/8" bore, designed for disc/drum, and mounts properly to the firewall. The wheel bearings were installed per kit specifications: "While rotating the rotor/hub assembly torque the nut to 17-25 ft/lbs, then back off 1/2 turn and torque to 10-15 ft/lbs"

[dne']

Ok, just putting out there what I do know. So are you leaning to think it's just the rod length? So I guess there is no slack between the arm of the brake pedal, it is tight and slightly pushed in according to your theory? So hypethetically speaking, if you were to loosen the master cylinder from the firewall after the brakes have become engaged and locked as when you have driven for a while, or take the arm of the plunger from under the dash off of the brake pedal arm, the wheel should loosen? what do you think?
dne'

[frog3]

Let's think about hydraulic brake operation. Brake fluid is pressed through the lines by a piston in the master cylinder. Once a critical pressure threshold is reached, the fluid can no longer compress and this pressure is converted to the mechanical motion of the calipers. The piston in the master cylinder therefore has to make a tight seal. Yet fluid is derived from and returned to the reservoir. So, if the pushrod is engaging the piston far enough to seal, pressure can build in the line as there is no return to the reservoir. That's my theory anyway, having not ever designed a master cylinder.

This doesn't seem to apply to my problem though, as when I drove home today I first tested the brakes by pumping the pedal. This did not result in a lock-up or hard pedal. I had to stop once shortly after my trip began to relieve pressure from the master cylinder. The remaining miles passed without issue, though I drove with utmost caution.

In any case, I have an adjustable pushrod and proportion valve on order. I'm looking now for the metering valve. Summit only seems to carry these remote bias adjusters. Can anyone suggest a source or part number?

[frog3]

Just thought I would let everyone know that a shorter brake pushrod solved the issue with the front brakes locking up. I've also installed a proportioning valve.

[dne']

I knew you could do it! no more worries, have fun!
dne'

[EvilPuppet]

Originally Posted by frog3

Just thought I would let everyone know that a shorter brake pushrod solved the issue with the front brakes locking up. I've also installed a proportioning valve.

How did you mount proportioning valve?
From the master cylinder to prop valve then to rear brakes?
Are your front brake lines still going trough original distribution block?