No fluid at rear brakes

[AJS240]

I'm working on a 1985 GMC K1500 truck (drum rear, disc front) brakes. I've replaced all of the steel lines (pre-bent kit) and rubber hoses, master cylinder, and rear wheel cylinders. I bench bled the master cylinder before installing. I removed the proportioning/combination valve from the chassis, removed the rear properning valve and cleaned it. The valve looks good and the two rubber seals on the proportioning cylinder look good. I bench bled the proportioning valve and centered the piston and have the GM centering tool installed.

With all of this the front brakes bleed fine and have plenty of pressure. I get very little flow at the rear and nearly no wheel cylinder piston movement after bleeding the rear. I get a little more flow at the union on the rear line part way up the frame when I test there. At the combination valve outlet to the rear I get decent flow (not as much as the front). The pedal is very firm and does not go to the floor.

Is there a spacer between the brake booster plunger and the brake master cylinder on these vehicles? Any other advice on how to proceed.

Thanks

[JohnnyPopper]

With all the new gear this sounds odd.

Are you asking about a spacer that might limit the overall throw?

Do you feel a physical limit to the brake pedal travel?

[VileZambonie]

If you have good flow to the height sensing proportioning valve but not after, just bypass it.