"HELP" Brake diagnosis on 1996 Silverado K3500

[Anthony Cozad]

Ok everyone please bare with me on this one. The truck is a 1996 Chevrolet Silverado k3500 dually 124,*** miles. I have done endless days and nights of research and diagnostics. I am about $3500 into chasing problems and have been to 3 or 4 shops now. The issue started when one day I got into the truck and made it 15 feet in my driveway when I gently applied the brakes and the rears locked up. Huge cluck sound and drug gravel for a couple feet. It wasn't driveable. I had it towed to a local shop and they replaced everything in the rear. They took it for a test drive and the ABS triggered at low speeds trying to come to a stop. You know the whole pedal surging deal. Found out the front wheel hubs were shot and the wheel speed sensors weren't reading correctly. Replaced those but then I had a really squishy pedal. I had a company called Les Schwab come out and they diagnosed the problem all the way to to what pointed directly to the ABS. They had bled the brakes like 6 times. Still remaining squishy. So then we bled through the ABS module and while doing so the pedal sank to the floor after a couple brake bleeds (on the module itself). It never came back to a solid pedal. I had NO brake pedal whatsoever. It was to the floor and it would still roll forward while in gear. Towed it to Les Schwab and they replaced my ABS module (the whole assembly) with one from a 1997 Chevrolet silverado C3500 dually 94,*** miles on it). Literally the same exact truck except mine is 4 wheel drive and the other is 2 wheel drive and also a year newer. Still squishy pedal but i just figured whatever its a chevy thing apparently. Anyway a few days go by and everything seemed fine till one day I had to stomp the brakes and the ABS anti-lock never engaged and I literally slid for 20 feet. All brakes locked up. No pedal surging. Wtf.... not working now? SOOOO The new issue I am currently having is the brakes are now really hard to press to stop the truck and the E-Brake light on the dash is on all the time. And it seems like the fronts are just locking up and the rears drag ever so slightly. There is no brake fluid leaks, everything is adjusted correctly. New ABS was power bled and brake lines have been bled a few times. So we are certain there is no air in the system. Maybe another bad ABS? What could be the chances...

I have:
New front brakes (pads, calipers, rotors, wheel speed sensors, and hubs). Including the one wheel speed sensor on the transmission for the rears.
New rear brakes (drums which have been turned, shoes, wheel cylinders, springs hardware kit and adjusted correctly and E-brake line adjusted correctly). With about 50-75ish miles of break in time on town driving and some highway driving.
New Master Cylinder with new fluid and no air in the lines.
Power steering fluid flushed and no air in the lines. The only thing left to replace before it is a full on overhaul is the hydrobooster and the power steering pump because the steering pump is part of the braking system. I would love to have my ABS assembly rebuilt and installed back onto my truck since it is the original. And no I do not want to bypass the ABS system. I would prefer to have anti-lock brakes on my truck as I tow with it all the time. I just don't know what or where to go from here. Thanks everyone that took the time to read this. Please any info helps.

 

[bluex]

The hydro boost has nothing to do with your issues. Don't spend money throwing parts at that part of the system.

I had issues with mine when I redid the rear and put new caliper an lines on the front. I even replaced the master chasing the issue.

My issues turned out to be incorrectly adjusted rear shoes. The light in the dash comes on because the combination valve (on the side of the abs pump) can't build pressure to one part of the system. From what I found its job is to build rear brake pressure first, once it does that, it'll start building front pressure.

To test this clamp off the rear flex line. It might take a few pumps to reset the combination valve but see if you don't get a firm pedal then. If you do, the shoes need adjusting. The wheel cylinder can only travel so far so if it's not properly contacting the drum you get a squishy pedal because you used most of the pedal travel before you got any pressure to the calipers.

I wound up deleting my abs before I figured it out. I think it was probably OK, but once I adjusted my shoes out to where I could just hear them dragging I got a much better pedal an the truck stops alot better. I had adjusted my shoes according to the manual for a 1 ton. I went back an adjusted them like I usually do drums (on cars or a 1/2 ton) an that's when I got a nice firm pedal. It's still not as good as my square body but it's the best it's been since I had the truck.

 

[Erik the Awful]

You need to find a shop that knows their @$$ from a hole in the ground.

Les Schwab either needs to give you your money back or fix it right, but can you even trust them to fix it right? Lord knows they won't give you a refund. It sounds like the local shop is just as bad.

 

[Schurkey]

I haven't heard anything about bleeding the ABS using a SCAN TOOL, which is REQUIRED. (See attachment.) "Power bleeding" the ABS is not the same as activating all the solenoid valves inside. This vehicle is crying out for some scan-tool diagnosis and bleeding.

Brakes can "lock up" on light application when the friction material is contaminated with brake fluid or axle lube.

I've only got experience with one Hydroboost system, and the brake feel is different from every vacuum booster I've used. I don't know if that applies to every hydroboost system, or just the one on my '97 K2500.