Three problems related to brake master cylinder have been reported for the 1998 Chevrolet K1500. The most recently reported issues are listed below.
Abs activation at slow speeds in traffic and at frequent stops, activation of abs started around 07/2005. Serviced parts included new rotors and pads, rear drums and pad shoes, abs modulator, and master cylinder. Vehicle still has same noted problem.
Brake pedal goes sponges and all the way to the floor. The truck had over 120,000 miles before rear brakes were replaced. In that time I went through 8 sets of brakes and rotors. In 2005 I rear ended a car at about 30 mph. The brakes went to the floor. Local chevy dealership replaced a defective brake booster assemble. This was the second brake booster/ master cylinder assembly replace on my truck since 2005. Since then. I have lost brakes on the truck 4 more times. Failed brake lines (leak and break) blown brake caliper and rubber hose. I am an ase certified mechanic. The rear brakes of the truck did not provide any braking assistance when inspected. Suspected fault was a defective design on the 1500 series truck brakes. When 2500 brake parts are used ( master cylinder assy, proportioning valve, and rear brakes change to 11" drums the brake pedal feels firm and the braking power of the truck is drastically improved. I've owned the truck for over 11 years as the second owner I bought it with very low miles. The brakes on the vehicle have always been terrible. I initiall spent over $2,000 at the dealership string to bet the brakes correct. In the end the dealer said that "this is how they all are".
Brakes had felt spongy for several months. Had the problem checked out three months ago, nothing found - brakes failed completely while driving, pedal went to floor , and vehicle slowed eventually. So there was no accident. Dealer replaced master cylinder at no cost (still under warranty).