SonnysSweetTea
Newbie
So I have a 1998 K1500 5.7. To start this off, I got a brand new brake booster 3 months ago before all of this which still works perfect. Now a few weeks ago i figured i'd take a shot at the caliper upgrade, swap a tahoe police pkg(8 lug k2500) calipers on and everything bolts up good even got some severe duty pads to try. No problems swapping, changed the rubber lines while I was under it, all went well. Took the truck out for a test drive, brakes still worked good but not great, had a bit of air trapped somewhere but the brakes could lock up and activate the ABS no problem. Took the truck down a dirt road to cycle the ABS like I've heard from some people. Activated it a few times at 40 mph, ABS works good. Heading back to the house the pedal was almost to the floor before the truck would slow. Obviously the master cylinder decided to go. It was original at 260k. Not bad.
Head to the parts store, swap a reman in, bench bleed, gravity bleed, then full bleed normal sequence RR-LR-FR-FL, solid streams, pedal solid when off, fire the truck up, pedal goes straight to the floor. No big deal just a junk M/C. Repeat this 6 more times with 6 more junk reman M/Cs. The last reman I put in I also took my truck on a trailer to the dealer and had them cycle the ABS with the Tech2 while pressure bleeding. There old m/c adapter was leaky so it didnt pressure bleed perfect but we vacuum bled the entire thing. Still the same thing, pedal goes to the floor when the truck is on. Decide to just do the NBS M/C swap, so I got a brand new one (not a reman) based off an '02 Tahoe. Bench bled it. Swap it in, carefully bend the lines back because it's a shorter M/C, hooked up the lines with one being an adapter. All good so far. Getting pissed off, I yank the drums off, shoes are beyond worn, and the one shoe is 1/2 inch from even touching the wheel cylinders. Replace both wheel cylinders, rear rubber line and got new shoes. Drums are still plenty thick no grooves or warping. All the hardware still good condition, all nice and tight, pushed the e-brake a few times to adjust the shoes properly.
Pretty much everything is new or in great condition still. Now that I have the NBS M/C with the newer style round cap that screws on instead of just popping on. I take the truck back up to the dealer and have them Truly pressure bleed it again with a better style adapter. Cycling all the ABS dump valves front/rear while under pressure, and doing the automated bleed procedure. All four bleeders all have perfect streams no air coming out at all. Almost 2 quarts of fluid just to be sure there is Absolutely No Air. Hop in the truck, pedal is super firm at the top, perfect pedal till you cant press any harder at 1/3 of the way down. All seems well. Fire the truck up one last time, pedal goes straight to the floor. It will stop the truck but your at the floor before you stop and when you bottom out, you still roll another 6-8 feet before a complete stop.
I'm stumped on what else there is. I've checked every line and connection and there's no leaks anywhere. M/C fluid level never drops, no leaks down the hard lines. I checked the booster rod and used a lathe to make a 1/4" longer rod which keeps the M/C 1/4" off the booster so it's not the rod adjustment. Checked the booster check valve, holds vacuum perfect, no sound. Literally every solution I've seen on these forums I've tried. I'm trying everything to keep the ABS module and try any last option, but other than getting a used module from a junkyard, I'm out of ideas. The last resort is just pulling the ABS module out and running a Wilwood adjustable proportioning valve and "T" the lines, bypass the whole ABS junk.
Head to the parts store, swap a reman in, bench bleed, gravity bleed, then full bleed normal sequence RR-LR-FR-FL, solid streams, pedal solid when off, fire the truck up, pedal goes straight to the floor. No big deal just a junk M/C. Repeat this 6 more times with 6 more junk reman M/Cs. The last reman I put in I also took my truck on a trailer to the dealer and had them cycle the ABS with the Tech2 while pressure bleeding. There old m/c adapter was leaky so it didnt pressure bleed perfect but we vacuum bled the entire thing. Still the same thing, pedal goes to the floor when the truck is on. Decide to just do the NBS M/C swap, so I got a brand new one (not a reman) based off an '02 Tahoe. Bench bled it. Swap it in, carefully bend the lines back because it's a shorter M/C, hooked up the lines with one being an adapter. All good so far. Getting pissed off, I yank the drums off, shoes are beyond worn, and the one shoe is 1/2 inch from even touching the wheel cylinders. Replace both wheel cylinders, rear rubber line and got new shoes. Drums are still plenty thick no grooves or warping. All the hardware still good condition, all nice and tight, pushed the e-brake a few times to adjust the shoes properly.
Pretty much everything is new or in great condition still. Now that I have the NBS M/C with the newer style round cap that screws on instead of just popping on. I take the truck back up to the dealer and have them Truly pressure bleed it again with a better style adapter. Cycling all the ABS dump valves front/rear while under pressure, and doing the automated bleed procedure. All four bleeders all have perfect streams no air coming out at all. Almost 2 quarts of fluid just to be sure there is Absolutely No Air. Hop in the truck, pedal is super firm at the top, perfect pedal till you cant press any harder at 1/3 of the way down. All seems well. Fire the truck up one last time, pedal goes straight to the floor. It will stop the truck but your at the floor before you stop and when you bottom out, you still roll another 6-8 feet before a complete stop.
I'm stumped on what else there is. I've checked every line and connection and there's no leaks anywhere. M/C fluid level never drops, no leaks down the hard lines. I checked the booster rod and used a lathe to make a 1/4" longer rod which keeps the M/C 1/4" off the booster so it's not the rod adjustment. Checked the booster check valve, holds vacuum perfect, no sound. Literally every solution I've seen on these forums I've tried. I'm trying everything to keep the ABS module and try any last option, but other than getting a used module from a junkyard, I'm out of ideas. The last resort is just pulling the ABS module out and running a Wilwood adjustable proportioning valve and "T" the lines, bypass the whole ABS junk.