djhoth

Just got my 85 cutlass, 74 olds 350, running after 8 yrs. I couldnt get my front brakes calipers to release when going through the bleed process. Rear drums,front discs,new calipers all around, new lines and hoses all around. The only things I didnt replace were the M/C and prop valve. I started the bleed process at rear pass side then went to drvr side rear. This went well but when I moved to the front I couldnt get the calipers to release and my brake light on my console is on. My peddle almost goes to the floor. I believe my problem is in the prop valve does anyone agree?

joe_padavano

The differential pressure valve (part of the combination valve) has a piston that slides side to side (and activates the BRAKE light) if there's a mismatch in pressure from the front to the rear circuit. Frequently this happens when bleeding brakes. The stock combo valves used a cast iron body, and rust can form in the bore, particularly if the car has sat for a while. This can cause the piston to be stuck all the way to one side, causing the light to stay on and preventing the brakes from being properly bled. A friend of mine has exactly this problem right now with a 72 Cutlass. You can disassemble the combo valve and recenter the piston, but if there's rust in the bore, you might want to simply replace it with a new brass unit.

djhoth

Thanks for the tips, its unbelievably hot here in Indy today so I'll postpone that till weekend. I always receive great advice on this website so thanks to all who chime in!!!

jimmyjam

The proportioning valve should have a button on the front of it, with a little rubber boot. Try pushing it. If not. ....
Take the boot off, the brass nut comes out clean it all out if you have to.
Did you bench bleed the master? If you did not, that is more than likely your issue.
On a bench you can force the plunger all the way forward, if you did it on the car, sometimes air can get trapped up in the front of the master. if you look at the master while its installed it points up, not the direction you want, while on the bench make sure the master is level.
While bleeding the brakes the pedal should never be pushed to the floor! Each time you push it to the floor it pushes the valve to that side.
If you have the tools just flare bend some brake line on each wheel from the bleeder valve to a bottle with brake fluid in it. Slowly pump the brakes so you dont foam the fluid.
The equalization of preasure should put the little ball back in its place.
Reinsert bleeders. Pump the pedal three times and hold it.
Open the bleeder slowly and the person pumping the pedal slowly lets the pedal sink.
The pedal should not go past the gas pedal as general rule, there is not need to go further.
Furthest wheels from master get bled first, by the brake line not the tire.