No speedometer and abs

[fmj]

Going to run it like it is until I get back from fishing. Will bring it in to diesel shop and have them look at tone ring (could look good to me but what do i know), and see if they can verify abs module and pcm. Mobile Masters don't seem to think its the abs since no code, so maybe pcm. Will have shop look at all three. Once I find out something I'll get back on here. Thanks for all the help.

 

[fmj]

Just a quick question before I go fly fishing for the week. How do you know if a tone ring is bad. Is it a visual inspection or is there some other way to "measure". I would assume that visual will have to be done with cover removed?

 

[DavidC]

Visual is the only way I know of but I think there should be a clearance spec between tone ring and sensor. May be able to find in service manual. It would require cover removal.

 

[fmj]

Thanks. I was looking in the SM today and all I could find was it wasn't a repairable item and would need to be replaced. Will go back an look at rear end section to see if there is anything there on tolerance.

 

[DavidC]

A little info courtesey Bob 4x4 a few years back.

The rear Wheel Speed Sensor (WSS) is mounted in the rear differential housing Rear Wheel Speed Sensor Location The WSS consists of a magnet surrounded by windings from a single strand of wire. The sensor sends a small AC signal to the CAB. This signal is generated by magnetic induction. The magnetic induction is created when a toothed sensor ring (exciter ring or tone wheel) passes the stationary magnetic WSS. Cab=controller ant-lock Brake.
The PCM uses a speed pulse input received from the Controller Anti-lock Brake (CAB) and internal programming to decide what vehicle speed and distance messages are required. The PCM then sends the proper messages to the instrument cluster circuitry on the CCD data bus. The CAB uses an input from the rear wheel speed sensor and internal programming, which includes a programmable pinion factor to compensate for different axle gear ratios and tire sizes, to determine what speed pulse output is required. The CAB then sends the proper speed pulse to the PCM on a hard-wired circuit.

 

[DavidC]

Some more from 2005. It's on a Durango but still applies.

If your truck is only 2 wheel ABS, then the tone ring in the differential could be the culprit. I owned a 99 Durango that the tone ring lost a couple of teeth. I openned the diff housing and saw the few teeth had chipped. The teeth, around 1/8" had worn off and were laying in the bottom of the housing. If the tone ring is missing a few teeth then the speed sensor and the computer do not know how to interpret the missing signals and as a result the ABS light is triggered. Before I dropped the diff cover I had replaced the rear speed sensor, the fuses, and I almost changed out the relay in the PCM.

 

[fmj]

Thanks. Looks like I will pull off the rear diff cover when I get back. Only looked at it from top with sensor out and obviously only able to see a few teeth. Damn just changed oil last month.

 

[Joe Mc]

Just a thought: If you could see a few teeth from the top with sensor out, could you not put rear on stands, chuck front wheels on both sides and front and back, put truck in neutral and look in as you spin the drive shaft?

 

[fmj]

Thanks Joe. But here is an update. Went on trip fishing and all was well (other than code for no speed) up and back. But about a mile from storage yard for 5er stopped at light and when i started loud snapping sound. Came from rear end. Got truck and trailer pulled into a park where I could disconnect. Truck wasn't going to go very far. Thought I chucked and axle??Got truck towed and to shop and after 6 hours ( don't use Good Sam roadside assistance) finally got trailer to storage yard. Today went to shop and the rear end is thrashed. So don't know if tone ring went bad or a bearing let go taking out everything. Will be fixed by tomorrow or Thursday. Further update when I get truck back.

 

[DavidC]

Expensive way to find the problem.

Dave

 

[fmj]

Isn't that the truth.

 

[Joe Mc]

Man that sucks! Silver lining, at least you'll have new innards and the "No Speedo & ABS" better be fixed = right...

 

[fmj]

Still in shop. Should be done next Monday. I wish I could ?know" if tone ring or bearing let go first or something else. I just changed the oil (done once a year) with synthetic two months ago. Didn't see any evidence of metal, and magnet didn't have a lot of metal or pieces. When I pulled the sensor out it wasn't loades with metal. Would like to know cause for sure.

 

[Joe Mc]

Tell the shop you want to see all the old parts. And their opinion on what failed/happened

 

[fmj]

Already did that. Their first opinion is bearing. But will lay out everything.

 

[DavidC]

Curious, what type of gear oil did you use?. Did it already have friction modifier or did you add it ?

Dave

 

[DavidC]

I have been looking for the air gap tolerance for the rear wheel sensor with no luck. Closest I found was a wheel sensor.
"Inspect the air gap between the face of the wheel speed sensor and the top surface of the tone wheel. The air gap must be less than the maximum allowable tolerance of 0.047 inch (1.2mm)." May be the same for the rear so it would be less than 1/2" or become erratic or no signal. It would be nice to use a dial caliper with the depth bar, remove sensor get measurement to top of differential from tone ring then if a problem arose like this you could check that measurement before all hell broke loose. At least when pulling cover for inspection/fluid change with the .047 you could at least check it while in there. My personal view on this dilemma is the Drivers side carrier bearing failed dropping the tone ring far enough from the sensor dropping the speedo.

Dave

 

[fmj]

Dave, I use Amsoil 75w140. It says no friction modifier but I always do figure 8s to see if there is any clunking. I haven't had to add with Amsoil. I've used Lucas and even though it says it also doesn't need modifier, I always had to add. When changing sensor I wondered about gap tolerance so I measured the old sensor (that worked at one time) and new sensor with depth gage and both were the same. The shop seems to think the bearing went. Will get to look at damaged stuff Monday. Marking all information down from you guys so I have it in future. This was a gamble thinking that it was the abs and could go on trip (300 miles round trip). Wrong.

 

[DavidC]

Sure doesn't sound like a oiling problem, weird that a bearing failed. Something you do not hear of.

Dave

 

[fest3er]

The bearings in my '98 2500 have been 'failing' since about 36k miles. They can be really loud, especially at 10-20 below zero. But they haven't failed catastrophically. Yet.