Hey everyone, I got some good help here brainstorming and getting details on these SUVs so I wanted to share a little write up on how I solved an issue where the rear brakes were sticking and dragging, it isn't what you would think!
I recently purchased a 2008 Suburban 2500 off of my father in law in Ohio and drove it back to Colorado. During the drive I started to notice that the brakes were dragging a bit and were starting to make a grinding noise. Thankfully it was -10 outside during the whole drive back in January so the brakes never did get hot.
After getting back to Colorado, I immediately ordered new pads and rotors at a minimum and would get more parts as needed once I dove into the project and saw what was actually needed. I suspected I would need calipers as well but wasn't sure how many. Below are pictures of some of the carnage. Don't judge me, I would have never let something like this happen if I wasn't in the middle of trekking 1200 miles! Somehow the brakes never did feel like they weren't braking well.
Unfortunately I didn't get a picture of the caliper. You can imagine..
So at this point I changed rotors, pads, brake hoses, rear calipers, and 3 of 4 caliper brackets. Sweet, all new shiny brakes (except the front calipers that were new in 2022). I go out to bed them in and after a few hard brakes and going through the heat up procedure, I decide to really step on the brakes and see how they work. This time, when I got off the brake pedal, it was as if I didn't. Full throttle wouldn't get me over 5 mph to try and get off the road the brakes were so locked up. Decided to try punching the brake again quickly and I heard a pop from somewhere in front of me maybe and the brakes released. I got back home and thought about it for awhile, "did I not grease the slides or the notches on the pads? Is it binding up? I did hear that pop, maybe the master cylinder is bad?" So I pulled the wheels back off and everything looked fine. Decided to change the master cylinder..
Well, turns out the hydroboost on these trucks is steel and when it rusts a bit, the master cylinder totally seizes to it so I ended up having to get a hydroboost to replace the master. I get them off as one unit and install new. I get side tracked because the hydroboost wants to preload the master cylinder. Long story short, you won't find this anywhere online but the GM hydroboosts seem to all preload the master cylinders ~1.5mm. I finally got the OEM pieces apart and it was the same preload.
I then proceed to go down a complete rabbit hole trying to get the air out of these brakes. For some reason, the air kept making it's way back to the master cylinder and wouldn't come out at any wheels until I opened a bleeder THEN had someone stomp the crap out of the pedal to jet the fluid through as fast as I could get it through. This seemed odd but hey, the air was out of the system finally. So I go for another test drive. Lo and behold, they still lock up.
The only thing left was the ABS valve block. I'm a mechanical engineer so I did a deep dive on how ABS systems work and found it plausible that this could be the problem. This is where I can share a little bit of wisdom back with the community. here is how I tested and verified the ABS valve block.
1. Took for a drive and got the brakes to drag several times. Using an IR thermometer I determined the rear right wheel is what was dragging predominantly.
2. This is the basic test that works 99% of the time. Removed the 2 fuses associated with the ABS system and went for another drive, no matter what the brakes wouldn't lock up.
3. To be thorough, I went back out this time with my scan tool watching live ABS data for the rear right wheel. Under heavy braking with no ABS activation, the brakes worked normal. If the inlet valve for the rear right activated even for a moment, the brakes would drag. Great, now we know it is the inlet valve in the ABS sticking for sure. Doesn't really matter because the whole block is a sealed unit but I like to know for sure.
Now I remove the ABS block. Thanks GM, I love you for placing it under the truck, against the frame, 2 inches from the floor, directly above a torsion spring, and all 6 lines going out of the top where you can't see. The potential for cross threading on reassembly is legendary.
Thankfully after 2-3 days of soaking the nuts and then using a mini butane torch on the nuts, they came out without too much trouble.
Now I go to remove the EBCM computer from the valve block on my workbench. This is where things got stressful. You ever try to stop a solenoid from moving when you electrify it? Or an electric motor? Yea, they get really hot because they just pull more amps and the coil overheats. Well the valves are just the armature of the solenoid in the ABS system and when the valve got sticky, the coil on the EBCM got really hot. This heat caused the plastic the winding was wrapped on to bubble and trapped it on the necking that traps the valves.
Well this sucks. They don't make this part anymore, It is unique to the suburban and yukon 2500s, I think it is even unique to this year. It needs programmed to the vehicle too if you get a new one. So I start scrambling to find a way to find a solenoid to solder to this board. I find out there are several vehicles with very similar boards as this is manufactured by a company called TRW. I find a board at my local junkyard that has the white solenoids out of a 2011 Ram 2500. There are two types of solenoids on these boards, black and white. Black is 5.5 Ohms and white is 2.2 Ohms.
I practice with the junkyard board and desolder the pins holding the board down and desolder a 2.2 Ohm solenoid. I then do all of the same to the board out of my truck. 42 through pins all desoldered, board removed from plastic case, old solenoid pins desoldered, new coil soldered to board, put everything back together and get it back on the truck. No communication.. My heart drops. I don't give up and I pull it all back apart, I find a missing component after ages looking over the PCB. I get my brother in law who is an electrical engineer and have him help me figure out which way this diode has to go back on the board. After getting it all resoldered a second time I try again. Heart pounding, plug in scan tool. It works! So I bled the brakes and fixed the issue after a few months of complete misery with this thing. Maybe would have been faster if I didn't have 2 kids under 2 running around.
I ran out of space for photos so I will post the PCB project photos in the comments. I hope this helps someone in the future who may be chasing brake issues. The abs units will corrode internally and stick if you never change your brake fluid. This was a complete nightmare from top to bottom but I'm happy to say it got fixed.
Thanks everyone who helped over in my original thread!
I recently purchased a 2008 Suburban 2500 off of my father in law in Ohio and drove it back to Colorado. During the drive I started to notice that the brakes were dragging a bit and were starting to make a grinding noise. Thankfully it was -10 outside during the whole drive back in January so the brakes never did get hot.
After getting back to Colorado, I immediately ordered new pads and rotors at a minimum and would get more parts as needed once I dove into the project and saw what was actually needed. I suspected I would need calipers as well but wasn't sure how many. Below are pictures of some of the carnage. Don't judge me, I would have never let something like this happen if I wasn't in the middle of trekking 1200 miles! Somehow the brakes never did feel like they weren't braking well.
Unfortunately I didn't get a picture of the caliper. You can imagine..
So at this point I changed rotors, pads, brake hoses, rear calipers, and 3 of 4 caliper brackets. Sweet, all new shiny brakes (except the front calipers that were new in 2022). I go out to bed them in and after a few hard brakes and going through the heat up procedure, I decide to really step on the brakes and see how they work. This time, when I got off the brake pedal, it was as if I didn't. Full throttle wouldn't get me over 5 mph to try and get off the road the brakes were so locked up. Decided to try punching the brake again quickly and I heard a pop from somewhere in front of me maybe and the brakes released. I got back home and thought about it for awhile, "did I not grease the slides or the notches on the pads? Is it binding up? I did hear that pop, maybe the master cylinder is bad?" So I pulled the wheels back off and everything looked fine. Decided to change the master cylinder..
Well, turns out the hydroboost on these trucks is steel and when it rusts a bit, the master cylinder totally seizes to it so I ended up having to get a hydroboost to replace the master. I get them off as one unit and install new. I get side tracked because the hydroboost wants to preload the master cylinder. Long story short, you won't find this anywhere online but the GM hydroboosts seem to all preload the master cylinders ~1.5mm. I finally got the OEM pieces apart and it was the same preload.
I then proceed to go down a complete rabbit hole trying to get the air out of these brakes. For some reason, the air kept making it's way back to the master cylinder and wouldn't come out at any wheels until I opened a bleeder THEN had someone stomp the crap out of the pedal to jet the fluid through as fast as I could get it through. This seemed odd but hey, the air was out of the system finally. So I go for another test drive. Lo and behold, they still lock up.
The only thing left was the ABS valve block. I'm a mechanical engineer so I did a deep dive on how ABS systems work and found it plausible that this could be the problem. This is where I can share a little bit of wisdom back with the community. here is how I tested and verified the ABS valve block.
1. Took for a drive and got the brakes to drag several times. Using an IR thermometer I determined the rear right wheel is what was dragging predominantly.
2. This is the basic test that works 99% of the time. Removed the 2 fuses associated with the ABS system and went for another drive, no matter what the brakes wouldn't lock up.
3. To be thorough, I went back out this time with my scan tool watching live ABS data for the rear right wheel. Under heavy braking with no ABS activation, the brakes worked normal. If the inlet valve for the rear right activated even for a moment, the brakes would drag. Great, now we know it is the inlet valve in the ABS sticking for sure. Doesn't really matter because the whole block is a sealed unit but I like to know for sure.
Now I remove the ABS block. Thanks GM, I love you for placing it under the truck, against the frame, 2 inches from the floor, directly above a torsion spring, and all 6 lines going out of the top where you can't see. The potential for cross threading on reassembly is legendary.
Thankfully after 2-3 days of soaking the nuts and then using a mini butane torch on the nuts, they came out without too much trouble.
Now I go to remove the EBCM computer from the valve block on my workbench. This is where things got stressful. You ever try to stop a solenoid from moving when you electrify it? Or an electric motor? Yea, they get really hot because they just pull more amps and the coil overheats. Well the valves are just the armature of the solenoid in the ABS system and when the valve got sticky, the coil on the EBCM got really hot. This heat caused the plastic the winding was wrapped on to bubble and trapped it on the necking that traps the valves.
Well this sucks. They don't make this part anymore, It is unique to the suburban and yukon 2500s, I think it is even unique to this year. It needs programmed to the vehicle too if you get a new one. So I start scrambling to find a way to find a solenoid to solder to this board. I find out there are several vehicles with very similar boards as this is manufactured by a company called TRW. I find a board at my local junkyard that has the white solenoids out of a 2011 Ram 2500. There are two types of solenoids on these boards, black and white. Black is 5.5 Ohms and white is 2.2 Ohms.
I practice with the junkyard board and desolder the pins holding the board down and desolder a 2.2 Ohm solenoid. I then do all of the same to the board out of my truck. 42 through pins all desoldered, board removed from plastic case, old solenoid pins desoldered, new coil soldered to board, put everything back together and get it back on the truck. No communication.. My heart drops. I don't give up and I pull it all back apart, I find a missing component after ages looking over the PCB. I get my brother in law who is an electrical engineer and have him help me figure out which way this diode has to go back on the board. After getting it all resoldered a second time I try again. Heart pounding, plug in scan tool. It works! So I bled the brakes and fixed the issue after a few months of complete misery with this thing. Maybe would have been faster if I didn't have 2 kids under 2 running around.
I ran out of space for photos so I will post the PCB project photos in the comments. I hope this helps someone in the future who may be chasing brake issues. The abs units will corrode internally and stick if you never change your brake fluid. This was a complete nightmare from top to bottom but I'm happy to say it got fixed.
Thanks everyone who helped over in my original thread!
