Thread: 1988 gmc k2500
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Old 05-09-2019, 01:28 PM   #3
Second Series
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Join Date: May 2015
Location: Tukwila Washington
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Re: 1988 gmc k2500

Thanks for the tip Mingoman, I have read about that in my on-line search, and itís even listed in the manual as one of the culprits. Iím trying not to throw parts at this, instead learning how systems work and troubleshooting to determine the fix.

I was going to put the two trucks in the same thread, but decided it might get even more confusing. Hereís my new truck:
http://67-72chevytrucks.com/vboard/s...d.php?t=786384

I have been reading on-line and in manuals about the brake system.
I tested the master and booster first because it was easy following this procedure:
With the engine stopped, press the brake pedal several times to deplete the vacuum reservoir, then press the pedal hard and hold it for15 seconds . If the pedal sinks, either the master cylinder is bypassing internally, or the brake system (master cylinder, lines, modulator, proportioning valve, calipers, or wheel cylinders) is leaking.
Start the engine with the brake pedal pressed. If the pedal sinks slightly, the vacuum booster is operating normally. If the pedal height does not vary, the booster or check valve is faulty.
With the engine running, press the brake pedal lightly. If the brake pedal sinks more than 10 mm (3/8 inch) in 3 minutes , the master cylinder is faulty. A slight change in pedal height when the A/C compressor cycles on and off is normal. (The A/C compressor load changes the vacuum available to the booster.) Leak Test
Press the brake pedal with the engine running, then stop the engine. If the pedal height does not vary while pressed for30 seconds , the vacuum booster is OK. If the pedal rises, the booster is faulty.
Turn the engine off and wait 30 seconds . Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.
That all checks good.

There is a long hill that I was riding the brakes down when I got the gravel before, I thought maybe that caused the burning. I went for another load of gravel, and changed my technique. When I got home and found the wheels hot, I jacked up the front and put it on jack stands. I rushed around gathering the jackstands, droplight and wrench. I finally opened the bleeder on each side and the fluid did not squirt out. I also tried to turn the wheels with the bleeder open and it was difficult.
This weekend I took off the calipers and lubed the pins, but they looked new. I also compressed the pads. When I bled the brakes before, I didnít do anything with the distribution block, or the isolation/dump valve. I read some more and found something about clearance between caliper and bracket. I had to hammer and pry to get the calipers off and on, so there was no clearance. I read about different kinds of calipers, floating and fixed, these are floating. I tried to file the edge of the caliper, but the file wasnít even getting the paint off. I dug out my grinder, but couldnít find a grinding wheel. I put 80 grit sandpaper and it worked great, took off enough and not too much. I put some sil-glyde on the edge, and the calipers went on easy. I pumped the brake pedal up and the wheels spin now. Iím still unloading gravel, but Iíll get it on the road next week.
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