Brakes

[Shrubby]

The brake pedal will not stop the 1979 ElCamino and brings it to a slow stop.When the car is on jacks the front rotors seem to stop fine but the rear brakes only slow the rear drums. Replaced the bad front pads. The back shoes are fine.
Replaced a caliper so I bled the system.
The brakes still bring the car to a slow stop.
I don't know if it's the master cylinder, brake booster or metering valve/junction block.
I don't want to throw parts at it.
Anybody have any suggestions?
Thanks,
Shrubby

[zeeb]

First it sounds like the rear brakes are a bit out of adjustment and/or you still have a bit of air in the lines. Start with the right rear, then left rear and bleed again. Then right front then left front. Metering valves don't go bad that often, and usually if booster is bad (vacuum) the pedal will feel stiff, like you are standing on a 2x4, it wont hardly move.

Since you seem to think the fronts are stopping okay,( I wonder since you say slow stopping) I would start with bleeding the rear, then move to the fronts for one more try at getting all of the air out. Crack the bleeder have a helper push the pedal slooowly down to the floor and hold it to the floor while you close the bleeder then have them release, sometimes if they pump it 2 or 3 strokes then hold it while you crack the bleeder open works too.Always make sure you get the bleeder closed before they let off of the pedal. Check the master cyl often and top off as needed while bleeding, let it get dry and you'll have to start all over.

[Shrubby]

I Bled the brakes starting with the right rear, then left, rear, etc. When the car is on jacks and the brakes are applied the front brakes will lock tight and can't be turned by hand.
When the brakes are applied hard the rear drums just slow down to a slow stop.
I agree the junction block/metering valve usually doesnt' go bad. The car has about 400,000 miles on it.
I'm begining to think its just the master cylinder because if it was the booster the front brakes wouldn't lock tight.
Any more ideas?
This doesn't seem to be too popular for mechanics to want to comment.
I've been doing brakes on the car for over 20 years and have never had this problem.
The back shoes are about half worn but I don't know what the thickness of the drums are.
Maybe they have been turned too many times and the shoes won't stop the drum.

[zeeb]

Okay, it sounds like the fronts are working okay, how tight have you adjusted the rears? We used to crank the adjusters out until you could feel a slight drag on the drum with the wheel off, turning it by hand you could even hear the shoe just rubbing the inside. A little friction wont hurt.
You might have something about the drums if they have been turned several times, they might be out of spec and too big to adjust out to.
Figure the rear brakes on most of those where 9 1/2" x 2" shoes, so measure your drum and see how big you are running inside to inside see how much bigger than 9 1/2 inches you are (if the drum isnt too rusted you might still be able to see the stamped number for max diameter on the outside edge around the lug stud holes)

With the fronts locking up so well, You would tend to believe the master is working okay..but one side could have failed, have you tried pulling the lines from the master and seeing what kind of flow you have direct from it? I guess if i had to start replacing parts i would begin with the master, it can be had remanufactured for about $21.00 (NAPA) the drums run about $37.00 each (cast drums...If I recall some of these also had aluminum drums)

Good luck, I will sleep on it and see if anything else comes to mind over night, I sometimes forget what I used to know amazing what slips the mind when you don't do this stuff every day anymore!

[Shrubby]

Put a used booster on and they work fine now.
Thanks everyone for your help.