The Stovebolt Site Forums The Shop Area Driveline centering proportioning valve

Hi Guys,

I installed a dual master cylinder with front disc on my 1950 1/2 ton. I have been having trouble bleeding the brakes because the proportioning valve is not centered. I looked and online and some have suggested to stomp on the brakes with the line that does bleed open. I just cannot get it centered so I can install the locking tool. Since it is under the floor board, it makes it difficult to see down into the sensor hole. Anyone else have a similar problem and have done this?

thanks,
skipper

The valve blocks the side with the least amount of pressure. Higher pressure forces the slider to the lower pressure side. If both side are low pressure ( air or no fluid ) the valve will not slide either way, it has nothing to move it. You must have fluid in both side, and then you can open the opposite side line and slowly move the slide valve back to center with the brake pedal.

Taking it apart is another option.

Many street rods do away with the proportioning valve and use residual pressure inline; 2# disc and 10# drum. It is not an on demand set up but works well.

This may or may not work for you. If you have the proportioning valve with the pressure switch screwed into the center, you can remove the switch and using a small pick move the slider to the center and put the switch back in. It’s been many many years since I had to do that.

I have used the procedure that Martin has suggested. Depending on the design, some of them will push the pin out the end, remove the rubber cap and push it back in to reset it.
Fred

Once you get the switch centered, either use a pressure bleeder or a MityVac pump on the bleeder screws to avoid displacing it again.
Jerry

Recently, I installed a new master cylinder. After bleeding the brakes in the old fashioned way (2 people; one bleeding, one pushing the pedal) the red light was on. A couple of stomps on the brake pedal and the light went out. ISTM that if the switch slider doesn't centre (light is still on), there is still air in the system.

Hi All,
thanks for the suggestions. I got the valve centered by moving it with a pick. I stuck it in the center hole and moved it. I then checked by installing the light switch and verifying that it is off. I then inserted the locking tool to keep it centered. Got my BIL to help me bleed the brakes and using the pushing the pedal method. We managed to bleed the brakes and get the air out where only fluid was coming out.
Before replacing the front drums with disc, the brake pedal was real high, always felt like my knee was way up to brake. The pedal would go down a couple inches of travel. Now with the disk in front and the new dual MC, the pedal travel is almost to 3 inches from the floor. Something does not seem right, I have a lot of travel before the braking begins to engage. I think I have to shorten the MC push rod so the pedal will sit lower down. How much travel does the push rod need to move into the MC to get full pressure of the MC? The pedal feels way different the the single MC with drums all around. we bled the brakes a couple times, made sure there was always fluid in the MC. The pedal still feels soft until it almost reaches the bottom?

Be sure the drums are adjusted correctly. Adjust till tight to the drum, then back just enough to rotate with a slight drag. Be sure to tighten the drum to the axle with the wheel or washers and lug nuts.

good point, I will check the drum adjustment

If you're running Bendix brakes, the above procedure will guarantee draggy brake shoes after a few stops. Adjust the shoes to get a firm drag (not locked up) and back the star wheel off one turn. That's 10 clicks on a normal coarse tooth wheel, or 20 on a fine tooth wheel that's used with self-adjusting brakes. Ignore any slight noise after you start loosening the adjuster- - - -the shoes free-float at the bottom and even a properly-adjusted brake might scuff a little until the brakes are applied and the shoes self-center.
Jerry

I believe I have Huck brakes and not Bendix on my 1950. I think the Bendix began is 1951, I never was clear about wheat the difference were but it seems the Bendix are the perferd brake.

The easiest way to tell which brakes you have (without taking the drums off) is by the location of the adjustment stars. For Huck brakes, there are two, one on each side of the brake cylinder, and they are at the top of the backing plate. Bendix brakes have one adjustment star and it is at the bottom of the backing plate.

My '51 3604 (8 lug wheels) had Huck on the front. I swapped them out with Bendix brakes (replaced the backing plates, drums, everything) so that I would have something that is easily repaired with parts from any auto parts store.

One thing to keep in mind is that with a disc drum set up, you want a master with about a 1 inch bore for a manual set up, little larger, like 1 1/8 for power set up. So you may have to check what you have.

Also, the disc/drum masters that are sold today, and even the drum drum masters sold today, no longer have the little duck bill residual pressure valve in them for the rear drum brakes, even though the master is specified for a disc/drum set up. So one thing you want to do is consider installing a 10 pound inline residual valve for the rear brakes . Wilwood sells them, red is 10, blue is 2. Keeps the shoes from fully retracting, which may be part of the problem.

The blue are used when the master is below the disc brake caliper. So if the master is under the floor, and the caliper is above that, you want to install a 2 pound valve inline for the front disc brakes. This may also be part of the problem.