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Q: brakes on 1996 GMC Jimmy

i hear a hissing of air when i apply the brake and somtimes it goes to the floor .I am not losing any brake fluid someone said brake booster is it hard to replace?can i just replace the diaphragm?
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To replace the brake booster diaphragm the brake booster has to be removed and disassembled. You sometimes do hear a slight hiss when the brake pedal is depressed which would be normal. The brake pedal will sink a little to the floor if the brake servo i working correctly. If the brake servo is failing due to loss of vacuum you loose brake assist and the pedal gets hard to press and takes longer to stop as you drive the vehicle. I suspect the problem may be more related to the brake master cylinder if the pedal "goes to the floor". Is your brake fluid fresh and Amber in color or is it dark black and merky? Contaminated dirty brake fluid can cause master cylinder failure.
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