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Old 07-14-2013, 12:06 PM
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Rear drum brakes won't lock up

I have a 37 Ford with disk on the front and drum on the back. I swapped out rear ends (1987 olds 3.23 to a s10 blazer 3.42) and now the rear brakes wont lock up. They barely come to stop when the car is on jack stands. I had good brakes with the Olds rear end.
The system currently has;
Dual disk/drum 1" master cylinder
Proportioning valve
Risidual Valve

I installed new wheel cylinders and shoes prior to rear install
Replaced master cylinder
Took proportioning and residual valve out of the system to test
Bled system many, many times
I am getting 600lbs of pressue at the wheel cylinder

At this point I can't help but think it is mechanical.
Any help at all would be much appreciated, before this old man pulls out what little hair I have left.

Thanks in advance for the help.

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Old 07-14-2013, 12:53 PM
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How did you adjust the rears. Are you sure the shoes are the correct size for the drums. Take a drum off and put the shoe in is and make sure it has full contact.
To properly adjust drum brakes, turn the adjuster until the wheels are locked then back them off 5-7 clicks.
If all this fails you may want to GENTLY step on the pedal with the drums off to make sure everything is moving. You need to go real easy or you will blow the cylinders apart.
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Old 07-14-2013, 01:39 PM
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I previously checked the shoes against the drums, they were OK.
There is no slot in the backing plate to get to the adjuster. I tightened them as much as I could and still get the drum on.
I did depress the brake padel with the wheel off. The front shoe moves out. The back will move out if I hold my foot up against the front shoe.

Thanks for your help. Any other ideas you can think of?

Ted
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Old 07-15-2013, 07:31 PM
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I would chalk the shoes completely slide the drums on, try the brakes and then check the contact area. Not sure what normal pressure is but 600lbs I would think is enough. Just curious, what did you use to check the pressure.
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Old 07-15-2013, 10:21 PM
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Make a slot in your backing plate. Easy to do.
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Old 07-15-2013, 10:34 PM
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Make a slot in your backing plate. Easy to do.
See, common sense to the fore.
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Old 07-16-2013, 04:16 PM
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I chauked the the shoes they are making good contact except the first couple of inches on the top of the shoe near the wheel cylinder more so to the outside of the of the shoe. All 4 shoes were about the same.

The pressure gauge I used was 800psi liquid filled gauge that I use to check tranny pressures. MP Brakes say the mininum pressure for drums is 400psi and 800psi on disk.

I will cut out the backing plate for adjusting.

Thanks for you responces.

Ted
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