Spongy Brakes, can't fix issues

[1972GMCsierra4x4]

Hey guys, I'm having some very frustrating issues with the brakes on my '72 K-2500. The truck has a Dana 60 with the big 12" drums. No matter what I do, the brakes are extremely spongy. I've had a complete brake job done, replaced the master cylinder, bled the lines several times and they still feel like I'm stepping on a plum when I try to stop. All tips and suggestions are greatly appreciated. Thanks!

[Zoomin]

Did you replace the flex lines?
Have you tried to pressure bleed the brakes using air to force fluid from the master out?
Did you bench bleed the master cylinder?

[LockDoc]

Originally Posted by 1972GMCsierra4x4

Hey guys, I'm having some very frustrating issues with the brakes on my '72 K-2500. The truck has a Dana 60 with the big 12" drums. No matter what I do, the brakes are extremely spongy. I've had a complete brake job done, replaced the master cylinder, bled the lines several times and they still feel like I'm stepping on a plum when I try to stop. All tips and suggestions are greatly appreciated. Thanks!

First off bench bleeding the master cylinder is important, so if you had the old one off or installed a new one make sure to do that....

Also make sure that the proportioning valve is centered as it should be.

On the drum rear brakes, one thing I found on mine is when you put everything back together and adjust the brake shoes you can’t just adjust them out until they start rubbing and quit. You have to adjust them out as far as they will go and you cannot turn the wheel or drum at all. This centers the whole assembly in the drum. (I even tap around the drum as I tighten them to help them center themselves) Then you back them off until the wheel just turns, and stop. If you only adjust them out until they start rubbing and quit, the first time you press on the brake pedal the brake shoe assemblies will center themselves and you will have too much clearance between the shoes and the brake drum. I also put three lug nuts on backwards to hold the drum tight against the axle on the rear.

I know it is a pain in the butt to try and hold the self adjusters off of the adjuster wheel while you back them off, but this is the only way I could get my drum brake shoes adjusted correctly.

LockDoc

[1972GMCsierra4x4]

Thanks for the tips guys. I couldn't tell you if the master was bled, I didn't install it. I need to replace my flex lines on the rear. I'll also try adjusting the brakes again