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92 S10 brake failure warning light

My 1992 (rarely driven “Home Depot” truck) just had the dash idiot light come one; it goes away when the brake pedal is pumped, and recurs in a few seconds. I was fortunately driving it in a field at the time, and it pretty much stopped brakes or no. My sense is the pedal is soft and sinking.

The mreservior has plenty of fluid. My guess is new master cylinder, but I wanted to know if I could test the vacuum bost, and whether tis a good idea to do pads/drums at the same time.

thanks in advance!


One of your two brake circuits is losing pressure. If you are not losing brake fluid from the reservoir or showing any leaks at fittings, calipers, hoses, brake wheel cylinders, or brake lines. It is likely a worn out master cylinder. It is unlikely to be the brake booster because the dash light turns ‘on’ with a pressure differential between the two circuits.

As to whether to change both the pads and shoes at the same time, I am in favor of doing one at a time. Do work on the other pair after the first pair are settled in and stopping ability is proven and acceptable.

Thanks for the advice! I more meant whilst I am replacing the master cylinder should I sieze the opportunity to do the pads.