proportioning valve

[marvxyz1]

I am about to install a new generic prop. valve in my 80 GMC. It has rear drums and front discs. Trouble is, I saw someone mention that, whenever the disc brakes are bled you have to compress the rubber cap on the end of the valve. I don't seem to be able to compress this end part . It doesn't seem to budge. Does anyone know anything about this???? Thanks for any info. you can give me on this.
marvxyz1

[Restrorob]

The way I understand, The only time you have to push the pin on the valve is if you don't get any brake fluid through the front or rear bleeders. Pushing the pin re-centers the valve. Start bleeding at the R/R then L/R, R/F then L/F.

[marvxyz1]

Thanks restorob, I've never replaced a prop valve, and I don't want to make any mistakes.. marvxyz1

[smills78gmc]

Subscribing to tread, I am in the middle of a complete front brake overhaul and have run into the same thing. I only get fluid to the left front caliper. By the way, I have replaced mc(bench bled) front calipers, and rotors.

[Restrorob]

Originally Posted by smills78gmc

Subscribing to tread, I am in the middle of a complete front brake overhaul and have run into the same thing. I only get fluid to the left front caliper. By the way, I have replaced mc(bench bled) front calipers, and rotors.

You may have a internal collapse in the right hose restricting fluid flow, The proportioning valve determines the amount of fluid sent to the rear verses front.

[smills78gmc]

Are you talking about the hard line at the back of the master cylinder or somewhere towards the back of the truck?

[Restrorob]

Originally Posted by smills78gmc

Are you talking about the hard line at the back of the master cylinder or somewhere towards the back of the truck?

OK, I miss read your post. You are not getting any fluid from the other three bleeders correct ? If so you need to check the proportioning valve to see if it's centered, And my other post could apply for no fluid to the R/F.

[smills78gmc]

ok, I will try to center the valve, from what I have read, It seems the best way to do that is with a piece of wood wedged between the frame and the valve. Do you know a better way? Thanks for the help

[Restrorob]

Originally Posted by smills78gmc

Do you know a better way?

I have just simulated slamming on brakes a few times (hit the pedal hard) and had them re-center them selfs. I have also had to remove the brake warning switch and use a pick to center them.

[smills78gmc]

I put a c clamp on the prop valve to center it. I now get fluid to the rear and the right front. Thanks for the help.

[Restrorob]

[smills78gmc]

Should I leave the clamp on the valve during the bleeding process or remove it then bleed the brakes? I have been pulling alot of fluid through the rear, but I still have lots of air in the lines.