Broken True-Trac

This is a 5 year update on the True-Trac unit that was installed in my rear differential, the 8.4" standard differential (not e-locker). My truck was re-geared to 4.56 and pushing 35" tires for the life of the unit. The unit functioned very well for what it was designed for, but for the past year, I noticed when backing out of a parking space and having the wheel turned, there would be a loud clunk after the first foot or so of tire movement. I assumed it was bushings, CV axles, something else - so I chased the problem around until one day when trying to turn my truck around in the driveway I felt the driveline bind up and there were several LOUD clunks that the truck seemed to push through. I mean these were severe enough binds that the front end of the truck was moving side to side when they happened. Thankfully, somehow, the damage was contained to the inside of the True-Trac unit, specifically the worm / helical gears had severe pitting and/or chunks missing. The ring and pinion seemed okay and I was able to rebuild the differential without further incident. This truck did not see any major off-roading or hard launches either, so I am surprised and rather disappointed that the life was so short.

The purpose of this post is for information, to provide a resource for someone who may experience similar symptoms, and to challenge the common idea out there that these units are "bulletproof".

When I initially drained my differential fluid, it had a metallic shine to it, however there were no visible chunks found. Most of the chunks remained in the differential as shown in these pictures. I learned from this event that you cannot just trust the fluid coming out of your differential to show the entire picture. There was also a rattling noise inside of the True-Trac when turning the pinion after disassembly. My backlash and preload were within acceptable ranges as well, not that that would have caused this much carnage.

Also, I don't see why Eaton claims disassembling these units practically "ruins" them and you won't be able to get them back together. It was clear after disassembly that these are rather simple units and other than putting the worm gears back in backwards, would be very simple to re-assemble.

 

Damn