1990 K2500 with almost 300,000 miles. This truck has RWAL. I have had problems with the right rear brake locking up for quite some time. When it is damp / wet it is really bad. I've had it to three different shops and this is what has been done.
New rotors & calipers, new rear drums & shoes, new master cyl, & power booster, new rear brake adjustment hardware.
Nobody seems to be able to fix it. I've asked the last shop about if the RWAL could be the problem but they did not think so. Does anyone have any ideas?

 

did you replace the rear brake hardware? (springs etc.)
Other than that, crusty old brake lines

 

Yes the brake hardware was replaced. The only things that were not replaced was the brake lines & the RWAL control box. The brake lines are original. I guess the lines is where I go next. After 300,000 miles that may be the problem.

 

Could it be the parking brake?

 

Don't think so. Parking brake cable was replaced a while back & seems to be working ok.

 

Do you by any chance know what the part numbers I would need to replace the complete rear lines set? I've looked online and am not sure of what I'm looking at.

 

Rockauto has rubber hoses, but not the hard lines. You may have to make them yourself.

 

Is it locking up (tire stops rotating) or is it dragging (tire rotates but there’s an obvious pull and/or smoke from the right rear)?

When does it happen - as soon as the brakes are applied or after driving for a while?

Is there anything you can do to get the wheel to release?

It’s unlikely the RWAL is causing it as the whole purpose of the system is to prevent wheel lock up, but a quick test is to unplug the control module - if the problem goes away, it’s a malfunction in the RWAL system.

 

When applying the brakes the right rear grabs,(locks up), real bad especially when I first drive it in the morning when damp/wet. After I ride the brake a little it is not as bad but still grabs. The wheel does release as soon as I let off the brake.
I see 3 connectors on the RWAL. Is this what I disconnect??

 

The 2 connectors in the 2nd picture are for the RWAL module - the one in the first is for the red brake warning lamp on the dash.

Will the wheel also lock up if you’re in reverse?

Other than RWAL issues, remove the drum for inspection.

Look for oil contamination due to a leaking axle seal.

Check for glazing on the surfaces of the drum and shoes.

Make sure the shoe with the shorter lining is positioned on the front and that all hardware is properly installed.