I have just installed a set of front disc brakes that I purchased from Skip Cain a few years ago on my 64 El Camino. I installed a new master cylinder for a 70 Chevelle and a new proportioning valve from OPG.I can get the front brakes to bleed, but not the rears. I have bench bled the master cylinder, but if I disconnect the line at the master cylinder to the rear system I cannot get any fluid to pump out, yet with bench bleeding all works well.
Any suggestions?

Thanks,
Dale

Seems to me your piston is covering the hole to the rears. Check your pedal engagement, something must be pushing it in a little.

Thanks for the reply. I also bled the master cylinder while installed in the car. I made sure all the brake lines are clear but I am unable to get any fluid flow from the rear port of the master cylinder when I connect the line to the proportioning valve. I did not connect the line at the proportioning valve. Is it nessesary to depress the pin under the rubber cap at the front of the proportioning valve to bleed the system? Of course this is assuming I can get any fluid that far!

Yes, chassis service manuals say you must depress that rubber button on the porp valve to bleed the brakes. Apparently there was a special tool to hold it depressed. It is like a short piece of flat metal, bent over at the end. you pust the button in with that bent end, then use one bolt on the porp valve to hold the button depressed. But a good wife would do just as well to hold the button down as you bleed. But I'd check your push rod going into the master first. If yours is not the exact right length, then you may be covering that hole as a prior poster advises. Also make sure you have the clevis and pin in the correct hole in the brake pedal. There are 2 holes in your pedal. One for manual and one for power brakes. Can't recall which, but search this site for many comments on this, or read your chassis service manual.

Originally posted by bhawk:
Yes, chassis service manuals say you must depress that rubber button on the porp valve to bleed the brakes. Thats only for bleeding the front brakes though. On my 70, that vavle (the one by the master cylinder) is only connected to the front lines. The rear line is separate and goes directly down to the distribution block.

Thanks again for all the responses. I held my finger on the button on the proportioning valve and when the brakes are applied I am unable to keep the button in. I have the clevis pin in the top hole of the brake pedel. Seems as though this is turning into a much larger deal then I had anticipated! Then again, this is what makes this hobby so much fun.

Thanks for all your help,

I use to have manual brakes and i converted to power. when i did this i had to move the pin in the pedal to the lower hole.