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Old 04-03-2012, 09:37 PM
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What am i missing in my brake setup?

So im loosing my mind on what my problem may be!

I upgraded my brakes on my truck, (62 gmc) from the drum/drum set up to a power disk/drum set up. I used a 79 chevy front clip with brand new brakes, CPP master cylinder, prop valve and a 82 drum set up in the back.. I ran all new lines and new cylinders and calipers. After sealing all my leaks, and bleeing the front and the back for hours i can still easily put my foot to the floor with the brake pedal. I have adjusted the rear shoes tight to the drum and still right to the floor with some amount of resistance. So aside from bleeing and bleeding what am i forgetting or missing?

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Old 04-03-2012, 09:48 PM
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Quote:
Originally Posted by luckynumberslevin
So im loosing my mind on what my problem may be!

I upgraded my brakes on my truck, (62 gmc) from the drum/drum set up to a power disk/drum set up. I used a 79 chevy front clip with brand new brakes, CPP master cylinder, prop valve and a 82 drum set up in the back.. I ran all new lines and new cylinders and calipers. After sealing all my leaks, and bleeing the front and the back for hours i can still easily put my foot to the floor with the brake pedal. I have adjusted the rear shoes tight to the drum and still right to the floor with some amount of resistance. So aside from bleeing and bleeding what am i forgetting or missing?
You bench bled the MC? MC not lower than the calipers?

There's a chance the MC sat around long enough for the seals to have hardened. This causes the fluid to internally bypass. Sometimes, exposing them to brake fluid for a period of time will bring them around. Sometimes not. Could be damage to one of the seals when the MC was assembled.

Other things could be a way out of spec pedal ratio, a severe mismatch of MC bore to the wheel bores.
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Old 04-03-2012, 09:51 PM
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Yes the MC is the highest point. ITs brand new and definatly was bench bled
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Old 04-03-2012, 11:46 PM
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Take the front tires off, and put a wedge of some kind behind the outer pad so the piston is forced in all the way. Then try your pedal. I have had new calipers that the seals pull the piston back far enough to cause this problem, paticularly with turned rotors. A 2 lb residual valve in the front brake line usually cures it, and causes no ill effects.
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Old 04-04-2012, 04:06 PM
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caliper bleed screws on top?
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Old 04-05-2012, 01:21 PM
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Yes the bleed screws for both the calipers and slave cylinders in the back are on top
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Old 04-05-2012, 08:14 PM
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Pull the rear brake line off the mc and plug the mc hole and just try working with the discs. This will help you isolate the problem. If the pedal still goes to the floor. ,Put the rear line back on and take off the front and plug that and see what u got. If it goes to the floor on both there is something wrong with the MC.
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Old 04-05-2012, 08:24 PM
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Quote:
Originally Posted by Cape Cod Bob
Pull the rear brake line off the MC and plug the MC hole and just try working with the discs. This will help you isolate the problem. If the pedal still goes to the floor. ,Put the rear line back on and take off the front and plug that and see what u got. If it goes to the floor on both there is something wrong with the MC.
I have to agree with Cape Cod Bob. I had the same problem and once I isolated front from back found bad MC right out of the box.
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Old 04-06-2012, 03:03 PM
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Ok so i did a little hunting and this is what i came up with.

I plugged the front line on the MC and only got approx 1/4 to 1/2 stroke on the pedal and then a dead stop. I removed the front plug and plugged the back, right off the residual valve and i was still able to put the pedal right to the floor. So then out of curiosity i put the lines back on normally and well the pedal still goes to the floor. Their is defiantly resistance but no hydraulic lock.
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Old 04-06-2012, 07:23 PM
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Quote:
Originally Posted by enjenjo
Take the front tires off, and put a wedge of some kind behind the outer pad so the piston is forced in all the way. Then try your pedal. I have had new calipers that the seals pull the piston back far enough to cause this problem, paticularly with turned rotors. A 2 lb residual valve in the front brake line usually cures it, and causes no ill effects.

Try this. Really. It is a common problem.
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Old 04-06-2012, 08:34 PM
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Quote:
Originally Posted by luckynumberslevin
Ok so i did a little hunting and this is what i came up with.

I plugged the front line on the MC and only got approx 1/4 to 1/2 stroke on the pedal and then a dead stop. I removed the front plug and plugged the back, right off the residual valve and i was still able to put the pedal right to the floor. So then out of curiosity i put the lines back on normally and well the pedal still goes to the floor. Their is defiantly resistance but no hydraulic lock.
So, you have proved that the front disc brakes are working properly.
Are you useing a combination valve? It sounds like you are and it is not balanced.
Go to MP brakes site for balance prcedure .
http://www.mpbrakes.com/
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