Differentials Overheating

Thought I would post this so that if anyone has this problem and happens to search "differentials overheating" it will show up and might solve their mystery also. Here goes....

Last February I was hauling a loud of logs out of the bay area in my new truck. After I got about 70 miles up the freeway I noticed my differentials temperatures were getting pretty high. The rear diff was at 260 degrees and the front was at normal for the ambient temp 160 degrees. I pulled over and felt the rear and it was very hot to the touch, so it confirmed that the dash temp gage was working. I checked the fluid level and it was full. I drove a bit further and had Petro lazor the diffs and the temp was confirmed at 260 degrees. I had them flush the rear diff and everything was fine after that. *(note, it wasn't the flushing that solved the problem)

Never had another problem with overheating until this past week when the rear diff got up to 270 degrees and the warning light came on. I pulled over, checked the fluid, sat and let it cool down and went on to the power plant and unloaded. As soon as I unloaded the rears cooled off rapidly down to 150 degrees. *(note, it wasn't the unloading that solved the problem)

Being totally puzzled I called the Peterbilt shop and talked to the head mechanic, he had no idea why this overheating would be occasional with over 5 months between episodes. He said if they were going out they would have just kept getting hot and eventually failed.

I was totally puzzled and called a ol' trucker who was my truck boss back when I first began driving.

When I told him that my differentials are over heating only on rare occasion he immediately said, "I bet you got full lockers and didn't back up a few feet to disengage them, next time you use them back up a little bit to let the lockers unlock, and the problem will go away".

Low and behold, the next time I used my lockers I didn't back up, the rears started warming up within 20 miles, I pulled over and backed up 10 feet and took off, the rears immediately starting cooling off....problem solved.

* What made the differential cool off on all occasions was the backing up. At Petro I backed up to park to eat dinner, at the power plant I backed up to dump my load, and the third time I took the advice from my ol' truck boss and I backed up to disengage the lockers.

I called the mechanic at Peterbilt I told him it was the full lockers causing the heat build up, and he wondered why they aren't disengaging when the switch is turned off and why I have to back up to get them to disengage...which is a very good question. From now on whenever I use my full lockers I just make sure I back up from now on when coming out of the woods.

When I get a chance I am going to call Eaton and ask if backing up is a required practice or should they disengage without having to back up.

 

He said all the loggers that had lockers used to always back in his day just before they hit the pavement. I don't have a Eaton manual on these full lockers. I guess I can do some googling and see what I can come up with. I'm just glad I caught it before I burn't out my rearend.