2nd Gen Non-Engine/Transmission Yes, another ABS issue!!

[Steve Robinson]

I just had an ABS sensor replaced to get rid of the dash light warning. Now, for the first time since I bought the truck, in a firm stop all is well until the truck is at a very low speed, maybe 5mph, then there is a very noticeable klunk like something has released, and a difference in the braking rate as though I've reduced pedal pressure which I have not. At normal easy braking, all braking characteristics seem as it has been for the last 160K miles, normal. I have not done a "lock-em-up" hard stop so I can't say what the braking might be like in that situation.

I will probably return to the place that did the work and I would like to have some idea of what is causing this behavior when I speak to the service guy.

Any of this sound familiar? Can anyone give me some advice and direction? I don't "wrench" but I'm not totally dumb either. Any ABS help?

 

[Road Dog]

You don't say what kind of ABS -- rear wheel or all wheel. On my '98 with rear wheel ABS the sensor output (on the rear diff) would drop to zero at low speed which the ABS module would interpret as a lockup and release the brake pressure. Great fun rolling up to a stop sign. At the same time the speedo would fall to zero (same sensor). Cleaning the connector contacts fixed the problem. When accellerating off a stop the speedo would stay at zero and then pop to 15k/hr. You didn't say what year. Earlier years used a separate speed sensor on the transfer case or transmission so the diagnostic with the speedometer wouldn't apply.

 

[Steve Robinson]

My 2500 is a 98. 5, 24 valve, 5 speed manual, and if I am not mistaken, the rear wheels are the only ones with the anti lock feature. What you describe fits my truck as far as the "... fun rolling up to a stop sign" part is concerned. I think the klunk I mentioned is coming from the brake shoes suddenly releasing from the drums. I will pay more attention to the speedometer and see if I notice anything irregular there, I don't think it is affected though, I'll check tomorrow morning. Even with the new sensor, do you suggest cleaning the contacts and is that a pretty obvious task when I get under the truck? I've gleaned, the sensor is mounted on the rear differential. Anything I should know about disconnecting the wire or plug or is that pretty obvious as well? Thank you for taking the time to offer your experiences and suggestions.

 

[Road Dog]

All the connectors are locking and there's a tab to push or pull or something and then the connector pulls off. Mud gets into it eventually so a cleaning with a small screwdriver and some dielectric grease to keep the water out helps. The sensor itself might not be seated properly. It's not adjustable but maybe the hold down bolt is loose.

 

[Steve Robinson]

I checked the speedometer and as yours was behaving, mine was doing the same; falling to zero before I stopped and not registering any speed until I was shifting into 3rd. I got under the truck and found the sensor was not seated fully into the differential and the mounting bolt was loose. The brake line stabilizing bracket was in the wrong position on the sensor mounting bolt. Both plugs on the wiring pigtail weren't fully pushed together. Altogether, not a very professional installation, if you ask me. I've made all of the corrections and the truck brakes normally again. Thanks for your suggestions and help.

 

[Road Dog]

Glad I could help. Sounds like they worked on your truck after happy hour.