GM-GMC: BRAKES, stock gm, rear brakes

Question
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Followup To
Question -
I HAVE A 1996 CHEVY CHEYENNE PICKUP. WHEN EVER IT RAINS OR THE HUMIDITY LEVEL IS ABOVE 74 PERCENT THE REAR BRAKES GRAB REAL HARD. THE BRAKE PEDDLE FEELS REAL HARD AND IT DOES THIS FOR ABOUT FIVE PRESSES ON THE PEDAL. THE TRUCK HAS BEEN BACK FOR WARRANTY THREE TIMES AND THEY SAID IT WAS DUST. I BOUGHT IT OUT OF WARRANTY.THERE IS NO LEVELING VALVE ON THE REAR END EITHER. LIKE I SAID EVEN IF THE TRUCK SITS FOR TWENTY-FOUR HOURS AFTER IT RAINED THEY STILL ACT UP. BRAKE LIGHT IN DASH HAS NEVER LIT UP. ANY IDEAS?
Answer -
Mark,  

 This is a little tough to help you with, without actually inspecting the rear brakes myself. I wonder if these are stock GM shoes in the back? I have run into problems with these being noisy and chattery a few times.....Mostly because they seem to be made out of really hard material. I would sugjest changing the rear shoes to an aftermarket set and having the drums machined. The problems you are having usually are signs of an axle seal leaking some grease on the shoes, but that should not really matter, if its wet out or not. I would really recomend that a good non-dealership shop take a look, very often with brakes its important to have a visual inspection. Hope this helps....
I ALREADY HAD A SHOP LOOK AT THE BRAKES. NO SEALS  LEAKING  LINING AT 80 PERCENT. RAINED THIS MORNING SAME ACT UP. AFTER 3 STOPS BRAKES CLEARED AND WORKED OK. AT FIRST REARS LOCKED UP AS USUAL PEDAL HARD AND PULSATING. ANY MORE IDEAS?

Answer
Mark,  

 Again I wish I could drive this truck myself. The pulsating you are talking about goes away? Otherwise there is definetly a warped rotor or drum somewhere. Also this Could possibly be a ABS problem, is your truck so equiped? and if so does the yellow ABS light ever come on when the truck is acting-up? It could be possible to locate and remove the ABS main fuse, this would put the brakes into a purely non-abs mode (your ABS light will come on when the fuse is removed)