Newport2004

Something very strange happened driving my 2004 Silverado 2wd yesterday. I was driving home about 35 miles on a highway, heavy traffic so mostly stop and go. I felt the brakes getting a little soft during the trip. Then about a mile from home I tried to stop at a light, the brake pedal went all the way to the floor and the brake light on the dash came on. As the pedal got near the floor there was enough braking force to avoid a collision and thankfully I made it home. Figured I had ruptured a brake line so this morning I checked all the lines and fluid level in the master cylinder, no leaks and fluid level is fine. I hooked up my Bosch serial port code reader and started the truck but no failure codes were logged. I figured pressing the brake pedal down to the floor would trigger the dash light and set a code but when I pressed on then pedal, it did not go to the floor, in fact it felt like normal. I bought this truck new and it has only 51000 miles. I've never had any brake service done, still on the original pads. I hesitate to drive it to a shop in case this weird failure occurs again. I've never had any car or truck with a brake problem that suddenly repaired itself. Any ideas?

mountainmanjoe

maybe the booster is going out

Newport2004

I figured if it was the booster, I'd have no "power" brakes but I would still have brakes by pushing really hard on the brake pedal. When my problem occurred, it felt like I lost all system pressure. The brake pedal went right to the floor with very little effort and not much stopping power

tech2

did the abs pump activate? If yes, the likely fault was signal drop out from one of the wheel speed sensors. This occurs at slow speeds only as the ac signal generated by the sensor is lowest at slow speeds. If the signal drops to zero the abs system thinks a wheel is locking up. the abs module will dump pressure to that wheel...the pedal drops deep to the floor and you lose some stopping power. no codes set as the system doesn't see a fault...its just thinks a wheel locked up.

This type of passive abs design has been replaced by active designs that don't have signal drop out.

the way shops determine this is to flight record all the wss signals and graph the results...the graph will show which signal dropped out.

without this equipment the best way to check is to remove each wss from the hubs....any that are seized in the bore need replacement. Rust forms and pushes the sensor away from the reluctor wheel. this increased air gap causes a weak signal output. When installing new sensors...clean off all the rust from the bore and mounting surface. The new sensor must slide into the bore will little interference.

Newport2004

Really good info, thanks for sharing! Not sure if the ABS pump activated. I do recall just a few minutes before the brakes failed the engine seemed to be losing power. I had to give it more throttle than usual to keep my speed up. Sounds like the wss failure might explain what happened. There is not much rusting at all on the undercarriage but the truck is 19 years old. Hard to imagine a brake booster or master cylinder having an intermittent failure that repairs itself. I can definitely envision a WSS or ABS module failing intermittently. I'll take a look at youtube for wss servicing. Ultimately it may be best if I have AAA tow the truck to a Chevy dealer and let them diagnose.

Newport2004

Just double checked the dash lights and it was definitely the red colored "Brakes" light that came on when the brake pedal went to the floor. The yellow colored "ABS" light never came on.

mountainmanjoe

Avoid stealerships. They'll look for expensive stuff to fix, but won't fix the issue. Find a trustworthy independent mechanic.

Newport2004

I was considering a small independent repair shop nearby but if I go that route and then get in an accident because they didn't fix the entire problem, I'll get sued big time and the small shop may not have very good insurance. If I let a dealer fix the problem and then get in an accident, their insurance pockets will be much deeper. Obviously the dealer will know this before attempting repairs and will probably insist on replacing the brake booster, master cylinder, ABS controller, all four WSS, the brake pads and brake fluid. The way the brakes failed on me was super scary. I'll call the dealer tomorrow and let you know what they say. Thanks again!

mountainmanjoe

dealerships also have expensive lawyers that know how to weasel out of culpability

Newport2004

Just got the truck back. $1377 for new master cylinder, new rear calipers, turned rear rotors, new rear brake pads, flush and fill with new brake fluid. Took them three days for lack of a couple parts. I suppose DIY would have been about $700 for the parts but I'll sleep better this way. Thanks again for all the help!