I just changed the fluid on my rear differential this morning. While working, I noticed an wire attached to an electrical connector on the top of the differential. What is the purpose of this connector?

I have pushbutton 4WD engagement. I assume it may activate a differential lock whenever I put it in 4WD. I notice that when the truck turns on dry pavement when in 4WD, it tends to bind. This doesn't happen in 2WD. I initally thought it may be binding in the front differential, but now that I see the connector, I believe it could be binding in the rear.

Also, when I start the truck from a near or dead stop and apply moderate to heavy acceleration, I can hear something clunk, sometime multiple times, towards the rear of the truck. I'm not sure if it is in the differential or possibly the suspension. It does this both going straight and on turns. If anyone can give me ideas on troubleshooting this problem, I would appreciate it. Thanks

 

The speed sensor for the PCM is located in the rear diff.

 

It is binding in the front. Those are your u-joints doing that. You do not want that to happen. You can wreck your u-joints VERY quickly by doing sharp turns in 4 wheel drive. Try to not do that.

It doesn't happen in 2 wheel drive because your hubs aren't locked which means your ujoints aren't doing anything.

-Matt

P.S. Keep those things greased! Every oil change preferably.

 

There is no locking differential on a ford truck. The binding comes from the fact that your transfer case is forcing the front wheels to turn at the same rate as your rear wheels. This is fine when you're going straight, but you are putting SEVERE strain on the truck when you're turning on dry pavement.

That clunk you hear when starting is probably a u-joint that you've broken or damaged by turn on dry pavement while in 4wd.

 

So that is the speed sensor. Thanks for the info.

FYI, the truck has the auto locking hubs. I would prefer manual, but they aren't broke yet, so I'll wait to convert them.

Believe me, I don't drive on dry pavement in 4WD. I should have clarified myself. If I am running 4WD, it is when the roads have snow on them. Although there is the problem. Since road conditions can vary, some places will have snow, others places are bare, I will usually leave the truck in 4WD until I hit a main road where I know it is totally bare. I always stop and put the truck in neutral to engage and disengage the 4WD, then move the truck to unlock the hubs.

I've had the truck bind about three or four times. Once was when I had disengage the 4WD and THOUGHT the axles were unlocked. The other times were as described above, snow covered roads where I had enough tire grip to make it bind on the turn.

I've replaced the U-Joints in the rear driveshaft about 5K miles ago. Inspected and greased them within past three weeks. Replaced drivers side front U-joints when I put new ball joints in three weeks ago. One was dry, but not damaged. When I changed the rear differential fluid this weekend, I removed the rear cover and used my fingers to slosh out the sump in the differential. No metal filings in the sump or in the bottom of the drain pan, so I don't think the differential has damage.

Back to the clunk in the rear. If it is a U-joint, how do I check for damage? Could it be related to axle rotation causing U-joints to bind? The truck does have a torsion bar at the rear axle. I also noticed that some of the rear springs are missing the plastic inserts between the leafs. Probably not the cause, but wanted to mention it.

Again, any thoughts on the noise would be appreciated.

 

The sensor is also for the ABS system and in 92 the sensor is used for both the speedo and the ABS system.