2000 GMC 2500 4wd - AntiLock Brakes Problem

[Murphy]

Hi folks,
I have a 2000 GMC 2500 4wd truck.. (SLE)

Every brake line on the vehicle has rusted out and I've replaced them one by one.. I've actually gotten quite skilled at what to do when I my vehicle's brakes fail in traffic.. (Practice makes perfect eh?)

The truck seems to have developed a strange problem with the brake system.

Whenever I come to a slow stop, the anti-lock brake system kicks in and makes a strong groaning sound and pushes back on the pedal. This only happens when the truck is just about to come to a complete stop.. It does not happen during the initial braking from higher speeds.. only when the vehicle is under 5 mph or so.

If I smack the brakes from highway speeds, the vehicle stops fine.

I also notice that it sometimes wants to pull to the right and it makes me think the problem is in the left front brake somewhere.

This groaning started off very intermittent about a year ago.. It would act up once occasionally when I drove the vehicle someplace. Now the problem has gotten worse and it does it whenever I stop.

I should note that when this issue occurs, the vehicle WILL NOT stop unless I pump the brake pedal once.. then it goes away and the vehicle stops as normal.

My brake pedal is NOT squishy and I seem to have good strong brakes when I'm decelerating from highway speeds.

What in blazes is going on?

 

[Bill325]

Some GM ABS units do not work at speeds below about 5 mph, by design. Yours seems to be doing just the opposite. Having to pump the brake pedal once does sound like an ABS problem. (First replacing the master brake cylinder is cheap, and eliminates that as a possibility.) A code reader that detects bad ABS wheel speed sensors might give you some information. I've also been told by a good mechanic that a particle of dirt that got lodged inside of the ABS unit can cause such problems. He recommended opening the disk brake caliper bleed nipple to force the piston back when replacing pads. Forcing the piston and brake fluid back through the system can cause dirt to get into the system.
Good luck with your brakes. I've had to replace all of the rusted out brake lines on my model year 2000 Sierra .