65 Chevy C10 rear drum brake woes. please help.

[Gumby83]

Hey fellas, i rebuilt my 65 c10 and put disc brakes up front. i planned to keep the drum brakes in the rear so i ordered a rebuild kit. I couldnt get the rear brakes to work after the rebuild.

Since i put in all new brake lines, hydrobooster and master cylinder i decided it must just have air trapped in them. so i bled them by pumping the brake.
still nothing....

bought a vaccume hand pump, and tried bleeding them like that.
still nothing.

Thought "Maybe the drums are really glazed?" so i used a die grinder with a flapper wheel to sand the inside of the drum.
still nothing.

bought an AC 110v vaccume pump and pulled a monster vaccume on the master cylinder...
still nothing.

I figured "maybe i collapsed the original 65 rubber hose from the frame to the rear axle" so i bought a new one.
still nothing.

So i bought a pressure bleeder. and forced 40psi of brake fluid through the system, bleeding over a litre through the rears.

Still.... Nothing.

I adjusted the adjuster through the slot in the drum each time. expanding it till it dragged hard and i cant get so much as a change in resistance with the brake. i swapped the wheel cylinders to another set...

Still Nothing...

What is going on here? did i rebuild the brakes with the wrong kit? is there a oddball drum or something? I looked for new drums, but couldnt find any with the slot in the front for getting to the tensioner/adjuster. i don't have a hole in the backing plate... i am really close to just buying a CPP rear disc brake kit, but i couldnt run 15 inch wheels then. If anyone has an idea, throught or suggestion please let me know. i am at my ends wit here...

[Braunschweiger]

I had the same problem with my '62, the previous owner had installed a master brake cylinder from the Corvette, which is for 4 disc brakes,
the residual pressure valve for the drums was missing, so the drums are not preloaded,
I solved my problem with a new master brake cylinder for disc/drums,
the residual pressure valves are available separately, so that it can be used in the rear circuit.
Was the bench bleeding carried out properly?
If the rear circuit does not work at all, even after repeated pumping,
although it has been properly bled,
then your new master brake cylinder is already broken.

[grubsster]

Did you "lock out" the proportioning valve when bleeding the brakes? Others on here can explain this better but, I used a cheap special made tool to bleed mine. It goes where the brake warning light would connect to the valve. Otherwise, I think the shuttle closes off the perceived failed half of the system. It looks like the one in the picture.

Good luck.

[Gumby83]

Originally Posted by grubsster

Did you "lock out" the proportioning valve when bleeding the brakes? Others on here can explain this better but, I used a cheap special made tool to bleed mine. It goes where the brake warning light would connect to the valve. Otherwise, I think the shuttle closes off the perceived failed half of the system. It looks like the one in the picture.

Good luck.

I don't know if i have a spot for that on my proportioning valve. i have one but it seemed way too big for mine. maybe i need a smaller one? i have an adjuster knob for bias. i've tried it every way i can. its almost like my wheel cylinders are too small and dont push the shoes out far enough or something.