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Joined: Jul 2011
Posts: 12
Grease Monkey
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Grease Monkey
Joined: Jul 2011
Posts: 12 |
On a few occasions after hard braking my brakes lock up. After they sit for an hour or so they release. Today I was out it was hot and the brakes locked up when I stopped. I could not move the truck for two hours. Any ideas how I can fix this?
I spoke to one truck guy who said that is a cronic problme with these trucks.
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Joined: Sep 2009
Posts: 6,689 Likes: 21
ChatMaster - 6,000
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ChatMaster - 6,000
Joined: Sep 2009
Posts: 6,689 Likes: 21 |
Sounds like it may have a failure of the inside of the hoses. Something is not letting the pressure release. Charlie 
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Joined: Nov 2001
Posts: 19,758 Likes: 64
ChatMaster - 15,000
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ChatMaster - 15,000
Joined: Nov 2001
Posts: 19,758 Likes: 64 |
Do they lock up both forward and back? If so it may be boiling brake fluid. Replacing Dot 3 with Dot 4 fluid might solve that problem as Dot 4 has a higher wet boiling point.
How Sweet the roar of a Chevy four!
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Joined: Jan 2002
Posts: 30,701 Likes: 141
ChatMaster - 25,000
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ChatMaster - 25,000
Joined: Jan 2002
Posts: 30,701 Likes: 141 |
Its common when the compensating port hole in the master cylinder is plugged. See shop manual picture.
Gene Schneider
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Joined: Nov 2007
Posts: 476
Backyard Mechanic
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Backyard Mechanic
Joined: Nov 2007
Posts: 476 |
The compensating hole is a very small hole in the bottom of the master cylinder bore, visible when looking down into the cylinder though the fill cap with a good light.
When you take your foot off the brake pedal to release the brakes, the brake shoe return springs at each wheel pull the wheel cylinder pistons back into their cylinders. In order for the pistons to retract, the hydraulic fluid in the wheel cylinders and brake lines must have someplace to go, which is back into the master cylinder via the compensating port. If the port is plugged up, or if the master cylinder piston rod is not adjusted correctly so that the primary piston cup edge does not retract beyond the compensating port, the hydraulic oil in the system cannot return into the master cylinder, and the brakes will remain applied, even though the brake pedal is released.
The latter condition can occur if you've had the master cylinder out for overhaul, or if you've re-bushed the brake pedal pivot pin bore. With the fill cap off the master cylinder, look at the bottom of the cylinder bore with a good flashlight. You will see two holes. The smaller hole, to the rear of the larger hole is the compensating port. Slowly operate the brake pedal with your left hand, while looking at the compensating port. When you release the brake pedal, you should see the rear edge of the primary piston cup move forward until it is clear of the compensating port. If the edge of the primary piston cup does not clear the compensating port, shorten the master cylinder piston rod by loosening the lock nut at the clevis and screw the piston rod a turn or two further into the clevis. After adjusting, operate the brake pedal again and check to be sure the primary piston cup is retracting to clear the compensating port. The shop manual says the edge of the piston cup should clear the port by .035" (1/32"). If you do adjust the piston rod, don't forget to re-tighten the clevis locknut.
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Joined: Dec 2001
Posts: 10,379 Likes: 1
Technical Advisor ChatMaster - 10,000
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Technical Advisor ChatMaster - 10,000
Joined: Dec 2001
Posts: 10,379 Likes: 1 |
Mark, what a great explanation. You did good.  
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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