Need help with diagnosing an ABS issue

[zakkb787]

Some of you may remember my thread from about a year ago about weird braking issues and my brakes randomly locking up. The truck hasn’t been driven much for the last year. Finally getting back to working on it and narrowing down the problem.

The issue is that after the brakes are applied moderately or heavily, they all 4 are sticking. Like locked down will not disengage horrible shaking all 4 smoking etc.

Things I’ve done so far:
Taken all calipers off and greased the slides multiple times
Flushed the entire system with a Motiv Power Bleeder with till fresh clean fluid came out of every bleeder
All new rubber brake lines
New master
New 2011 LML booster

The problem still persists. No dash lights like malfunctioning ABS system or brake or anything at all. On a whim I decided to unplug the driver wheel speed sensor to disable the ABS and took it for a drive. Zero sticking issues at all no matter how hard or easy I was on the brakes. (Obviously the ABS light comes on with the sensor unplugged) The truck has 2 year old Timken bearings with new WSS so I don’t think that’s my issue. My question is how do I go about further diagnosing this? I’m assuming it’s either an ABS pump or module issue but I’m not sure how to narrow it down any further, and honestly I’m not really 100% sure how either of these would be causing this but definitely seems ABS related. I did not do an ABS bleed after any of the flushing or replacing the master but the problem is the same as before any parts were replaced so I don’t think this is the issue. Plus the system was never ran completely dry since flushed with a power bleeder and the master is above the ABS pump in the system. Any help?

 

[Ron Nielson]

There have been some recent posts on another forum by several people who seem to have similar problems to yours that just stepping on the brakes "very hard" while stopped solves the problem. Very hard to some is like slicing almost melted butter to others, but I don't think it would damage anything. In any case, you could progressively step on the brakes a few times to see if any improvement. And it's free. If you try this let us know.

 

[zakkb787]

That is what I tried originally and was able to diagnose the problem this far. When driving somewhat normally and giving myself ample room to stop with the ABS functioning, the brakes are perfectly fine. In fact, they’re great considering I have fairly new pads and rotors along with a fresh fluid flush, new hoses, master, and lml booster. The problem is when you jab them or have to stop fairly quickly or are in traffic, the brakes are not disengaging at all. So 1/2 to full brake pedal engagement. I’ve also confirmed this by really getting on the brakes quickly and as hard as I can, and with the ABS engaged, none disengage. This is originally why I replaced my booster and master, as I was concerned maybe the booster was not disengaging properly as well as the booster was seeping fluid down my firewall. However, this didn’t fix the problem. A few hard jabs and they’re right back to sticking. But with the ABS disabled, the problem is gone. I can ride the brakes however hard I want and they don’t stick. They’re actually impressive considering how crappy these brake systems are from the factory. That’s why I need help narrowing down exactly what the culprit could be.

 

[Ron Nielson]

Let's see, ABS hooked up, brakes stick. Disengage ABS, brakes work normally. Conclusion??

 

[zakkb787]

Let's see, ABS hooked up, brakes stick. Disengage ABS, brakes work normally. Conclusion??

Conclusion: something in the ABS system is messed up. I’m asking for help on how to diagnose which part of the ABS system could be causing the issue because A - I do not have a ton of knowledge on all of the ABS system parts or how exactly they could cause an issue like this and B - I don’t want to throw a ton of money replacing the entire ABS system when it’s possibly only one part needing replaced

 

[Ron Nielson]

There are 2 parts to an ABS - the valving (BPMV) and the circuitry (EBCM). I have never heard of anyone repairing the valving but the circuitry (circuit board) is sometimes found with broken solder joints. You can find videos about removing and repairing this part.

 

[zakkb787]

There are 2 parts to an ABS - the valving (BPMV) and the circuitry (EBCM). I have never heard of anyone repairing the valving but the circuitry (circuit board) is sometimes found with broken solder joints. You can find videos about removing and repairing this part.

Thank you for the PDFs and info. This is exactly what I was needing to figure out how to begin diagnosing.

 

[Chevy1925]

you need to perform an ABS bleed in the system. its not uncommon for junk to get into the abs valves when you do a regular flush (pushing fluid through from the top or pulling from the bottom). if the bleed doesnt fix it, id put money the module is bad. You can verify that by getting the brakes to lock up and then cracking the incoming lines into the module to see if fluid shoots out, if not, then crack the outgoing lines and see if fluid shoots out. if it does on the outgoing but not on the incoming, its the module.

to check electrically, id use a scan tool and verify its reading wheel speed sensors correctly. if one is still showing speed from a short in the sensor, it will probably keep the module activated. a scope hooked to each sensor would also verify the signals are good feeding bavck to the module.

 

[zakkb787]

you need to perform an ABS bleed in the system. its not uncommon for junk to get into the abs valves when you do a regular flush (pushing fluid through from the top or pulling from the bottom). if the bleed doesnt fix it, id put money the module is bad. You can verify that by getting the brakes to lock up and then cracking the incoming lines into the module to see if fluid shoots out, if not, then crack the outgoing lines and see if fluid shoots out. if it does on the outgoing but not on the incoming, its the module.

to check electrically, id use a scan tool and verify its reading wheel speed sensors correctly. if one is still showing speed from a short in the sensor, it will probably keep the module activated. a scope hooked to each sensor would also verify the signals are good feeding bavck to the module.

Thanks James. I’ll try to do a bleed when I find someone with a scanner that’ll do it. And thanks a million for the troubleshooting steps