71 Cutlass SX Conv. Bled the brakes after new master, front was OK, never got any pressure to the rear, got some fluid, maybe gravity. Is there a way to re-set the proportioning valve?

 

on the end of the valve that feeds the front brakes is a rubber cap under that cap you will find a pin sticking out push that in... might be hard to push but push on it with a hammer handle to centre the valve and then bleed the rears again

 

thank you, I'll give it a try!

 

The button does nothing but disable the hold-off (metering) valve for bleeding the brakes. It won't reset anything - you'd have to push the metering valve all the way through the housing before you even contacted the differential pressure switch piston.

More to the point, look at the cross section of the combo valve below. If the differential pressure switch piston has moved all the way to the right, as would be the case if flow to the rear brakes was cut off, how does pushing in on that button on the left end of the valve move the piston to the left?







If the problem REALLY is due to the differential pressure switch piston having moved to the right, first try opening one of the FRONT bleeders and standing on the brakes hard. That may recenter the piston (and will likely push it too far the other way). Once you get it moving, you can use open bleeders and careful pedal pressure to get it centered. If that doesn't do it, disassembly is the only option.