98 K2500 'burb brakes

Bullet_98 · May 1, 2017

Greetings, I thought I would check here before I do something drastic. 1998 Suburban K2500 454 gas w/HD rear brakes. I've been spinning wrenches for over 30 years so I'm not a novice but this one has got me. The brakes haven't been right since I got it 3 years ago. I've done the following, new rotors, turned drums, new calipers, complete drum hardware kit, wheel cylinders, all three rubber lines, plus two master cylinders, one rebuilt, one new Delco. The brakes are still crap. There's two inches or so of free fall and I swear it speeds up, then they start engaging, it stops but requires a good bit of pressure to do so, way more than it should with hydroboost but not like manual. The back brakes are clearly doing the most work as it will slide the rear in gravel or a wet road if you grab them hard. I pull a 30' camper and have to pray to the brake controller every time I need to stop in a hurry which happens no matter how you try to plan and anticipate papaw's next move in front of you. There are no lights and they are still there, the light at ignition on. My best guess is the ABS box is somehow bypassing or leaking pressure between the front and rear circuit. If I adjust the back brakes until they start to scrub a little on the drum and I get in stop and go for a bit, they will pump up until they are too tight. My next move pending advice here is go to the older style non-ABS master cylinder and eliminate the box. A couple questions, does the box also do the job of proportional valve? If so I would need to add one. I've got 20 days until we leave again, any help or advice would be appreciated. Thanks

Bullet_98 · May 1, 2017

That should say "they light" at ignition on meaning the amber abs and the red brake.

Bullet_98 · May 16, 2017

If anyone is interested and wants to permanently fix your spongy brakes, here's what I did. I removed the master cylinder and entire ABS assembly. I used a master cylinder from a 85 K30 4x4 with 13x3.5" rear brakes. It is casting number 1925. It has a 1 5/16" bore vs. the 1 1/4" bore the Suburban came equipped with. I put a Summit Racing disc/drum proportioning valve on. I was able to reuse all the lines but had to change the fitting on the drum side where it goes to the valve and both lines going to the front brakes. I pulled the ABS fuse and bled the system. Now for the first time since I've owned this vehicle I trust the brakes. Only thing left to do is make a small brace to bolt to the valve to support it. I mounted the valve with the ports to either side, they are much easier to fit the lines that way. I am sure the brake warning light can be hooked back up, when I get a chance I'll check the connector to see which wire has power and then change the end to attach to the old style switch. Must have tools would be a compact bender that will handle 3/16 and 1/4 line, a compact tubing cutter, a double flare tool, assorted wrenches.

grampadirt · May 16, 2017

Good deal,glad you found a solution.The brakes on my Burb have always been superb,just a little toe pressure on the pedal and it stops.The only thing that annoys me is the self adjusters in the rear don't work for sh!t,I have to adjust 'em myself occasionally.In fact every GM truck(had a few)I've had they've never worked well,even with all new hardware.Same goes with wife's '99 Burb.

Bullet_98 · May 16, 2017

I agree on the self adjusters, never seen any work right. The brakes you have are exactly what I expect from hydro-boost. I had a 93 K3500 and a 98 K3500 and both of them stopped like that and thankfully, now my burb does too. I don't know if the issues was in the proportion valve that attaches to the ABS module or what but it was dangerous to drive. I was never able to make them pulse. Someone had told me if I could get the ABS to activate it would take care of the problem but even with both feet and all my 270 lb weight on the pedal, it never tried to pulse or lock a wheel. Now I just smile at all that apparatus as I look at my scrap pile, lol.