car has Nova drums all around. have been using a newer disc-drum master and decided to change to a drum-drum master to get away from touchy front brakes. changed master and drove car about 4 mi. and felt there was probably air in the lines yet. bled them again and tried it and pedal was hard like no power. checking found rear port of master plugged. I apparently hadn't cleaned it well enough after it was smoothed and painted. was able to get it unclogged. rebled everything and still hard pedal.just in case it was the fault of the new master I put the old one back on and still had hard pedal. beginning to think that maybe the booster had taken a dump. but decided to try bypassing the distribution block in case it was clogged also. agian rebled everything and now don't have any pedal. I was under the impression after taking to some that with drums all around the distribution block wasn't needed. What's Wrong? any ideas? I'm at the point where I'm frustrated as hell and not thinking things through clearly enough

Hi Jack,
The (distribution block)called apportioning valve, is nothing but an expensive light switch. They don't give much trouble unless they sit around and get rusty inside. So you can py pass it, and clean things up. I just can't think of anything that would cause you to get a hard pedal. Have you bench blead your master cyl before puting it in your car? When you bench bleed Never push the plunger in more then 1 inch or you could damage your master cyl. If no one else knows about hard pedal, I'll call some of my friends.Regards,HonestFrank
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"VEO DINDICE"

yep I've bench bled them every time they were off. thats how I found the new one had a clogged rear port. even put a rebuild kit in it when I found it had clogged, didn't make any difference. as I said I have no pedal since bypassing the distribution block. the fronts do work (barely) rears not at all.I know this because it's on the jackstands and I can turn the rear drums by hand but not the front. guess I'll probably just have to go through the system line by line, joint by joint.

That brake distribution block is a royal pain. It is not a proportioning valve and is on all GM cars of that era. Disc cars have an additional proportioning valve block.
The block is a pressure switch that also serves for the low fluid alarm light. If it gets plugged up it will give you that hard pedal and also will often keep the rear shoes from releasing on time resulting in hot drums.
Been there over and over with several cars and going thru it again on my 68 Impala. Problem is that the block is no longer available from GM or repro so junkyards are the only choice. My latest one came from Arizona where brake line moisture is minimal.
Ive been told by several mechanics that bypassing the block is not a wise move. You can try flushing it out with denatured alcohol, dont use any other solvents except brake cleaner.
If anyone has a NOS one I'm a ready buyer!
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Carl
Automotive gold is everywhere; you just have to learn how to dig for it

Oh, the GM # is 3906933 if anyone is lucky enough to run across one at a swap meet.
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Carl
Automotive gold is everywhere; you just have to learn how to dig for it

Have you tried Hemmings Motor news for the part you need? The Chevy section is about as big as the "GONE WITH THE WIND" script!!! Fred P
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Fred P.

I managed to find a few thru Hemmings and even one off E-Bay over the past few years but Ive come up dry in 6 months of searching this time around. With so many late 60's era GM's on the road Im suprised someone hasnt repopped it!

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Carl
Automotive gold is everywhere; you just have to learn how to dig for it

looks like I solved it. haven't put the car back on the ground and driven it yet. I want to bleed it with the wife pushing the pedal rather than just the suction bleeder. problem seems too have been crud in the rear wheel cylinders. put new ones on tonight and it seems to be OK.