Bad or weak rear brakes?

[TonySS]

When I had jacked up my 1987 Astro and was trying to find where the annoying highspeed vibrations where coming from I noticed that I hardly could stop the rear wheels from turning when I had the transmission in drive and the engine idling. I had to press very hard on the brakepedal to stop the rear wheels. I know the front discs are doing most of the braking on cars but I really thought that it would be easy to stop the wheels from turning when the engine only was at idle. I’ve recently changed brakeshoes and brakedrums and they are adjusted correctly. I’ve also tested the combination valve to be sure that it can detect a low pressure condition in the rear brakecircuit.

Is this normal? Has anyone tried this?

The braking force from the parking brake seems to be much greater then the normal service brakes.
(Sorry for my bad english)

Regards,
Tony

[cousincletus]

Make sure your parking brake isn't overadjusted. Try loosening up the cables, then readjust the star adjuster. Are the shoes wearing evenly? Is the "short shoe" in the front? May possibly be the flexible rubber hose obstructed. Are you getting a strong stream of fluid when you bleed the rear brakes? Maybe the hose needs replacing.

[TorinoGT69]

Possibly the wheel cylinders are sticking, is the shoe wear even?

[TonySS]

Thanks för advice. The shoe wear is even and the pistons aren't stuck. It looks normal when I bleed the brakes but perhaps there still could be a clogged brake hose? But I wonder if it should be possible to easily stop the wheels from turning when I apply the brakes, as it is now I have to press very very hard before the rear wheels slow down. They do however stop easily when I apply the parking brake with the engine idling and transmission in gear (drive). How much force on the brake pedal should be necessary?

Tony

[drew300]

Does an '87 have anti-lock rear brakes?
Otherwise, there's a brake-proportioning valve in the line. It limits the pressure to the rear drums, so the disks get most of the pressure. Maybe this is sticking?
But I'm not a brake expert