[chrisinestes]

I have a 1999 GMC Sierra 1500 4x4. It's got this ongoing brake issue... Feels like it's got air in the system. The anti-locking on the brakes just barely activates when on gravel, and not even close on something with more traction.

It's got a new GM anti-lock pump/module, new rotors, new pads, and has several system bleeds with the scan tool & auto bleed stuff built into the system. The tire are the correct size... 265-75-16, if that matters

Anyhoo, do any of the cheaper ($20 to $120) OBD-2 scan tools/readers allow access to the built-in-to-the-truck auto-bleed stuff? $100 per time taking it to a shop with the $5,000 scan tool is getting old!

Maybe the brakes are functioning correctly, and they just suck. It sure seems like they used to work a lot better, though.

Thanks!
Chris

[salem1912]

New calipers? Four wheel disc?

[chrisinestes]

It's 4-wheel disc with C-Clip rear end. Discs & C-Clips don't seem like a good combo to me. I don't think they did that for very long... Maybe 2 model years.

The calipers are original & never rebuilt. The GM tech that replaced the ABS pump/module says he checked all the calipers and they were fine, but I guess I don't really know. It's had 2 new master cylinders, and there was no change in braking.

I've had 2 shops bleed the system with the auto-bleed. I was present during the last bleed, and we ran half a gallon of fluid through the system, and there was no change.

I forgot to mention a vibration when braking... Feels like a warped rotor. Sometimes it's bad, sometimes it's not bad, sometimes it's not there, sometimes it's when it's cold, sometimes it's when it's warmed up. It's had new rotors twice, too, with no change in the vibration. Maybe I need to look towards the calipers.

I don't know... It's frustrating. I can't afford a newer truck, I can't afford to just throw money at this one.

I found that the cheapest OBD2 scan tool that'll do the auto bleed stuff is around $300.

Chris