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Old 05-06-2013, 04:44 PM
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Dragging disks GM Combination valve

I'm using a GM combination valve on my disk/drum setup. It's the proper one with the metering valve, but I'm getting light front disk dragging once warmed up. I have adjusted the rod between the MS and the booster at least 6 times and am still getting dragging once the vehicle heats up. I even disconnected the vacuum line to the booster and still slight dragging.
My question is can the metering valve be adjusted at all so the disks get slightly less pressure than they currently have? Also I had a guy install the brake lines and he ran both front brakes off of a single front outlet on the combo valve. Would this have an adverse affect on the system? The other front outlet is being used for the brake pressure switch.
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Old 05-06-2013, 06:12 PM
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Try adjusting the rod between the pedal and the booster.
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Old 05-06-2013, 07:30 PM
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That's my next plan of attack. I already had to cut about 5/16" portion of the threads off to get the linkage to rest without being preloaded into the booster. I'm thinking maybe as pressure builds it preloads even more. So next weekend I will be cutting another 1/8"-3/16" of threads off to see if I can eliminate the dragging. After driving awhile like this the brakes begin to let out a constant squeak which is quite annoying.
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Old 05-12-2013, 09:44 AM
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I agree with 46streetrod, this type of complaint is usually too tight of clearance between the booster and master cylinder. The front brake line issue you mentioned shouldn't be a problem. Also, make sure the weight of the brake pedal itself isn't pressing on the booster. Install a pedal return spring if you don't have one.


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Old 05-12-2013, 12:46 PM
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Man I'm really having trouble getting these brakes dialed in! I drove it to work this week and after driving about 20 minutes pressure builds up and the brakes drag. Shut it off for a few minutes and it goes away for awhile only to come back. I have adjusted both rods all over the place and I either get pedal to the floor or full pedal stroke before solid pressure right at the end of the stroke, but that's when the pressure builds and causes dragging.

Am I supposed to have a firm brake pedal right at the top of the stroke? With mine I have about 80% pedal stroke with what feels like light vacuum assisted braking, but the pedal really does not get firm and stop until the very end of the stroke and thats when I get the pressure build up. If I adjust the rod ine turn off then the pedal gies to the floor without any stopping pressure.

Any insight is help is very much appreciated guys. I want to drive my truck?
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