Replacing speed sensor

It is in the top of the rear diff

You folks are talking about two different sensors. The vehicle speed sensor is on the left side of the transmission as STEVEN KENNEDY mentioned. The sensor on the top of the rear differential housing is strictly for rear-wheel-anti-lock, (RWAL) brakes, and nothing else. If the truck has four-wheel anti-lock brakes, it will not have that sensor. Unlike the cheaper version on GMs that use a three-channel system, Chrysler has always used a four-channel system that modulates the two rear wheels independently of each other. That uses a wheel speed sensor at every wheel.

You should be starting new questions specific to your vehicle for a couple of reasons. First, the first person didn't even bother to list the engine size, transmission type, two or four-wheel-drive, or the mileage. Those are all factors in answering the question of how hard it is to replace the sensor. We're lucky they told the model year because prior to 1989 models, they did have a speedometer cable screwed into the vehicle speed sensor. A failed sensor would only cause the cruise control to be inoperative, and the transmission's lock-up clutch to not engage. Other than that, there would be no symptoms and the speedometer would work just fine. We also look at the mileage to make generalizations as to the best suspects or best places to start looking for a diagnosis.

The second problem is this was a private conversation between two people. Others are welcome to read the responses when researching their problem, but when you piggyback a reply, it is only going to be seen by the two individuals involved originally. We get automated e-mails directing us back here when a new reply shows up. None of the other experts will see the addition or have a chance to reply. That does a huge disservice to the person making the addition and may not get them the help they need.

Posting a new question also adds to the list of similar problems so we can see what is common.

If anyone needs it, here's the link to post another question:

https://www.2carpros.com/questions/new

Check ABS system for codes and repair and that should clear up the speedometer issue
most common the rear axle speed sensor