Mosh

I just pulled the steering wheel on my recently purchased 96 Cummins to rotate it into correct position after installing a rebuilt steering sector a few months ago. I was careful to reconnect the cruise control multipin connector properly before putting the center cover back on the wheel. For whatever reason the speedometer and odometer ceased working about the time I did this work. Maybe not related, but very suspicious. Took time to take the cover back off and check the connection again. Still doesn't work. Went to Dodge dealer parts man and he suggested that the sender on tail end of auto transmission may need replacement. Ordered the part. Speedometer will occasionally flicker when driving like there is a short in the connections. Anyone have ideas on where this problem is?

Stamey

The sensor on the rear end is the one that determines the speedometer reading. The one on the transmission just tells the PCM to pay attention to the rear end sensor, and is involved in tranny shifting. You got an ABS light on too?

Chris

Mosh

Thanks for taking the time to comment on this Chirs. Looks like I need to get ahold of a schematic. Abs light is not on. Both odometer and speedometer are not working. When I see blips in speedometer that come erratically when driving the odometer will add a tenth or so based on how much of signal is there.

v8440

Remove the sensor in the rear axle. It's on top of the housing, and I think you need a 9/16" wrench to remove it. See if there are metal shavings on it. It has a magnet in it and will attract shavings if there are any circulating in the gear oil. If not, reseat it in the rearend, taking care to ensure it is as far into the hole as it can go. Then, tighten the retaining nut back up.

Inside the rearend is a reluctor wheel. Basically, it's a thin steel plate with a bunch of little teeth on the circumference. These teeth pass the sensor as the carrier rotates. Since it has a small magnet in it, the sensor functions as a hall effect device, and it generates a little pulse each time a tooth passes it. Anything that interferes with the passing of the teeth through the magnetic field will mess with the output of the sensor.

If you pull the sensor and the tip of it is chewed up or mechanically damaged, immediately stop driving the truck and pull the rearend cover to see what's wrong. Not likely, but very important to do if it is damaged.

If none of this is the problem, the sensor may just be bad. Or, there could be a wiring problem between the sensor and the ecm or pcm, whichever it is.

Mosh

Thanks very much for your specific answer on trouble shooting this. I will do this and post the results. Appreciate your experienced comments very much.

turbo thom

Very good answers. But if you have no ABS light, I would go to the sensor in the tail housing. But either way, this will a very good learning experence.

..Preston..

v8440

I got my experience with all this in an interesting way-broken spider gears in the limited slip unit. What happened was, it wheelhopped at the track. A few days later, the speedometer went crazy-dropping to zero, then bouncing back up to actual speed. Then, it just dropped to zero, and never moved again (until repairs were made). I still didn't make the connection between the wheelhop and the dead speedometer. When the rearend started popping going around corners, I went home and dropped the pan. There were spider gear teeth lying in the bottom of the housing. What had caused the erratic speedometer readings was that some of those pieces had gotten wedged up against the tone ring that goes past the sensor. Those pieces warped the tone ring, so that it no longer consistently went past the sensor, and actually ground part of the sensor off.

I doubt that's your problem, unless you've been really hard on the rearend very recently. I can't remember if my abs light came on-I think it did. Apparently, if the abs light is not on, it points to the sensor in the transmission. Either way, it's entertaining and expensive when you start breaking dana 80 parts. Hopefully you have not done that.

Mosh

Thanks again. Today I installed a new tail shaft sender that I had purchased from my dodge dealer prior to coming here for help. Earlier poster mentioned that this sensor is involved with transmission shifts. Anyway, it was a little bit of a corrosion battle exercise as the plastic insert had a steel bolt retaining it. Wouldn't come out. After a little straining and cussing, I ended up getting base of the unit out of the aluminum taile shaft housing. Of course found that the bolt holding the outer piece on was rusted solid with a steel bushing splined and pressed into the plastic. Knocked this bushing out and saved the piece. Put new sendor in, plastic drive gear was fine, and held it together with a new 1/4 inch SS bolt and nut. Regarding the rear end...I am not showing hte ABS light, but Speedo is still not working and am going to take a look tomorrow at this differential sender unit. Don't know where else to go at this point. Will make sure I get a good look at the star wheel that this sensor looks at. I did not hurt the rear end. Nothing torn up in there. Only puzzle for me is that you fellows seem to all agree that I should have an ABS light on. Don't.

Stamey

You may have popped something elsewhere. I am trying to impart the knowledge I have to help troubleshoot this, but you may have popped a fuse someplace that I don't know about.
As far as the senders go. I know my tranny would not shift out of first when the tranny sender went bad, and I have been told that the tranny sender tells the PCM to pay attention to the signal from the rear-end sender.
When the rear sender has a problem you get an ABS light in most cases, and the speedo doesn't work.
Wish I could tell you more. You might have to go back into the steering column and look for pinched wires or something else that's out of place.

Chris

v8440

Good thing about the rear sender is that it's positioned to where it can catch some oil and grease from the front of the truck, thus hopefully not rusting. You won't be able to see the reluctor wheel unless you can get your head above the rearend and look down in the hole. Even then, you'll only see a small part of it. If you pull the cover, you'll be able to see a bunch of it at once. It is possible for the sensor to be bad and have suffered no mechanical damage. It is also possible that, like others have said, the problem lies elsewhere entirely.

Mosh

Thanks again. You fellows are giving a good take on this situation in my opinion. Will check the rear sender, but going back to my first post, am suspicious that I did someting wrong with the connection inside the steering wheel. Just don't know what. Not too complicated. Just the multipin connector for cruise control and the two pin for air bag deployment. Even rechecked to see that I had the two halves mated properly a second time. Also checked the fuse block for a blown fuse. Read owners manual and it showed the entire cluster off one fuse. That fuse was good and other instruments are working properly. Got me scratching my head. Would help to know what kind of signal is going through the multipin cruise control. I have a multimeter. Cruise control is not working, but wouldn't if the speed sensor input was not coming to it. I probably screwed this all up by turning the wheel inside the truck on the spline shaft to lign it up after putting in a new steering sector shortly after buying truck. Driving the truck home from New Hampshire was a real drill. **** steering was so sloppy that I had to constantly be on it avoid whacking someone on interstate. You fellows have been helpful here. Appreciate the comments. This is up to me to find this at this point as I am only one here. You fellows have pointed me in right direction.

Mosh

I have confirmed that the rear axle sender is putting out a good signal. Segmented wheel could be seen well from sender inlet cavity and is in great condition as one of you said, being lubricated by the rear end lubricant. Have traced the wiring up to the front of the chassis and need to check for continuity. Found some corrosion in the two plastic connection blocks along the way, but after cleaning the connections, still had speedo function. Can anyone point me to a link where I can see what the circuit looks like for this speedometer assembly? Thanks, Mosh

Mosh

Correction: "Still had no speedo function.

infidel

If you have a 4wd the speedo sensor is on the transfer case.
If it isn't functioning correctly no cruise or speedo.
The sensor is available at most autoparts for around $30.

Mosh

Am posting what I have found out on this problem. Finally took this to my dodge dealer after I could find no problem with senders or hard wiring. They have a knowledgeable tech who impressed me. He placed an analyzer on the truck and found 0 signal coming from the ABS control module under the dash. He explained that this module receives signal from rear axle sender first and then passes this to ECM, I believe, and then to speedo. He concluded that problem is either wiring (power supply or ground to module) or bad module. Said would narrow but would need another hour or so. I had to go that day. New module is $292 (way too much but what can you do). Both he and parts man stated that speedometers rarely act up. If do costs about $600 to $700 in order to replace and get odometer set....ouch. Anyway looks like I need a new ABS module. Also to hopefully end the sender location debate here....he states that sender on rear axle has dual purpose to provide ABS and speedometer signal. Absense of any output form ABS control device apparently explains why I was not seeing ABS light on dash. Will provide followup once this is fixed. Also, just lost fuel gage. What the hell is going on with my 96 electronics?!?. Read up on this on this board. Looks to be tank sender. MOSH