[68FB400]

I've got a '68 FB with 4 piston front disc brakes. Set up is Master cylinder, Proporting valve and distribution block. Problem is the proporting valve is leaking and a replacements are limited and rather expensive.
I've noticed on a '69 front disc car it is a different master cylinder and only a distribution block.

Can I go with a '69 style master cylinder and skip the prop valve?
Also, car pulls to left on braking. Have new/rebuilt calipers and bled several times.

Any help would be appreciated.

Wayne

[68FB400]

I've got a '68 FB with 4 piston front disc brakes. Set up is Master cylinder, Proporting valve and distribution block. Problem is the proporting valve is leaking and a replacements are limited and rather expensive.
I've noticed on a '69 front disc car it is a different master cylinder and only a distribution block.

Can I go with a '69 style master cylinder and skip the prop valve?
Also, car pulls to left on braking. Have new/rebuilt calipers and bled several times.

Any help would be appreciated.

Wayne

[mike nixon]

if the car pulls left while braking and you've replaced calipers i'd put hoses on the front.

probably what's happened is the rf hose has collapsed internally or has a restriction of some sort in the line. this applies the lf front caliper causing the pull.

regarding the prop valve. what it does is restrict pressure to the disc brakes until the drums [rear] have been applied.

there are a couple of options open to you regarding this.

you can install a manual prop valve and adjust it until the brakes work properly.

you can install a 70 or later unit that's built into the distribution block and mounts on the frame.

you can have the orig rebuilt or buy a replacement for it. the are a couple of topics in this forum regarding the companies that do this.

mike

[Jim Doran]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by mike nixon:
regarding the prop valve. what it does is restrict pressure to the disc brakes until the drums [rear] have been applied.

mike<HR></BLOCKQUOTE>

Mike, I think you have it backwards.

A proportioning valve is used in the REAR to decrease the rate of pressure rise to the drums relative to the pedal force as weight is shifted to the front during braking. This prevents the rear from locking up under hard braking conditions.

- Jim Doran -Some Pics of my 65

[PMDRACER]

On the earlier cars, there were 2 parts inline from the master cylinder. First, there was a large round cast iron proportioning valve near the master, and down on the frame was nothing more than a basic brass looking T fitting, tying the lines together.

Later cars, starting in '69 (but not all '69s), the 2 piece setup was dropped and a one piece cast iron prop valve was mounted to the frame.

The job of the prop valve is to balance the brakes front to rear, and to pressurize the rear lines before the front lines see pressure. Otherwise, the car would nosedive. A third job of the later type is to house the switch for the idiot light. If you end up with a severe enough leak in the front or back, the switch will close off that side of the valve, grounding it, and turning on the idiot light on the dash.

You must have some sort of a prop valve in the car, and it has to match the application. The drum/drum, disc/drum and disc/disc prop valves will all work differently.

The same goes for master cylinders. They must match the application.

If you want some info on some brake upgrades, see my "other" site: PMDRACER

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. bill@tigerefi.com

[68FB400]

Thanks for the input!

I actually located a replacement prop valve from Rick's Camaro (Firstgen.com). They offered 2 choices: Buy a rebuilt original for $195 or a new aftermarket for $125. To boot, they are willing to buy the old core back for $90.

['ol Pinion head]

There's a reason why some of us started pulling all of the rebuildable metering valves 14 years ago...