Help with brakes before I pull my hair out

[cofferson]

hopefully you can download and zoom in to see it.

Thank you!

 

[DodDel5-3-6L80e]

TLDR: I was having brakes sticking issues. After replacing everything I can't get a firm pedal. Wondering if ABS valve failure is common.

I own a 2008 Suburban 2500. The brakes were dragging so I started going around all four corners replacing pads and rotors. I also replaced the rear calipers (fronts are newer) and and guide pins and caliper brackets as necessary. Greased everything up and bled the brakes easy enough. Went for a drive and all felt fine but quickly turned sour. Brakes started dragging and then after hitting the brakes particularly hard, they stayed fully engaged. I punched the brake pedal, heard a light pop and the brakes released. At this point I changed the soft lines thinking MAYBE those were bad. They were perfect all the way through. I then figured that since it sat for a long while, it may be that the master cylinder piston is sticking. Replaced both the master cylinder AND the hydrobooster because the hydrobooster was leaking. Thankfully I did this because they were seized together and still are. I bench bled the master successfully and put the new parts on and went to bleed the brakes. Never really got any air out. Now I have an extremely soft pedal. Pull the lines back off and air got back in the master. Bench bled it again and put on vehicle with plugs and got a very firm pedal. Put the lines on and this time I didn't use a vacuum bleeder incase I somehow sucked in air, still a very soft pedal. So now I used a scan tool to bleed the ABS and still never got air out. At this point I'm at a loss because brakes are very simply. I feel like I'm chasing a ghost and at this point the only thing I can think is the ABS module has something wrong with it and once I replaced the master cylinder I basically screwed myself. Truthfully I don't know exactly how the valving works to understand the root cause myself so I'm wondering if anyone here has thoughts on if this could be the abs unit? It may even be that the ABS is what was causing issues all along and now it's either not allowing air through due to valves sticking or it's bypassing the pressure.

Thanks guys. I really want to get this on the road and it's making me highly regret even buying it even if that's an irrational thought..

Are all of the wheels breaking? My first thought is a bad caliper.

 

[Fless]

The diagrams are free on www.charm.li. Here's an example but you'll want to change to your model and engine if needed, using the links at the top. (Scroll down on the page below for JH6...)

Electronic Brake Control Module — 2008 Chevrolet Suburban 4WD V8-6.0L Service Manual | Operation CHARM

Detailed repair manual for the 2008 Chevrolet Suburban 4WD V8-6.0L.

charm.li

 

[cofferson]

Are all of the wheels breaking? My first thought is a bad caliper.

It's a faulty ABS valve block which ended up causing issues with the EBCM as well. Once I get it all back together tomorrow I'll make a new thread doing a little write up of how I ended up diagnosing and fixing this issue incase anyone else has this in the future.

 

[DodDel5-3-6L80e]

Glad you found it. What a mess.

 

[Rocket Man]

The diagrams are free on www.charm.li. Here's an example but you'll want to change to your model and engine if needed, using the links at the top. (Scroll down on the page below for JH6...)

Electronic Brake Control Module — 2008 Chevrolet Suburban 4WD V8-6.0L Service Manual | Operation CHARM

Detailed repair manual for the 2008 Chevrolet Suburban 4WD V8-6.0L.

charm.li

I did not know that, thanks. Bookmarked.