2nd Gen Non-Engine/Transmission Replaced Brake Lines now ABS issues?

[Bigiron]

A friend with a 2000 3500 DRW had brake lines replaced and brakes bled but now when slowing downn at about 20 and slower brakes vibrate and it acts like the ABS is activating. Vibrates the pedal and does not want to stop. Any suggestions? No lights or codes just vibration and fading brakes.

 

[fest3er]

ABS probably *is* activating. Re-check the wiring and connections from the speed sensor in the rear diff all the way through to the CAB (Controller, Anitlock Brake). You'll probably find that the signal voltage is dropping below a threshold, causing the ABS to think the wheels have stopped turning and engage. Check the power connections to the CAB. Also check the ground; there should be a bonding post near the fender. Check the voltage between that bonding post and the battery's negative post; it should be almost zero (maybe a few tens of millivolts).

Search back 8-10 years; you should find a few of my posts about what I found with the Abbott speedometer adjuster, including voltages and thresholds.

 

[Bigiron]

Ok thanks, we'll start there. Funny they worked perfect until a steel line started to leak and he had it replaced.

 

[HBarlow]

I've never worked on the newer systems but I believe bleeding the braking system after a line replacement is complex and involves multiple steps according to a prescribed procedure. If the person who replaced the brakeline was not a dealer tech, familiar with the procedure, he probably created the problem.

 

[BigDaddy]

Did they bleed the ABS Module?



There are one or two bleeder points on the module that have rubber caps.



You should bleed these and hopefully that will correct your problem.

 

[Ramtuf1]

Take the truck out onto an old dirt road and do a hard stop to activate the ABS braking. Do this several times and then try to bleed the brakes again. I have had this symptom but it ended up being my hub bearings. I replaced both and that took care of the activation on ABS when coming to a stop on dry roads. The signal level must have been marginal