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

 

I just came across your almost two year old post. I just had the exact same issue with my True Trac LSD. I have the same 4.56 gearing but only running 32’s, and I had the exact same symptoms. I have had mine in for 3 years now and would have thought it would have e ran for years to come. I do no off-roading with exception to the occasional forest service road. My differential shop was backed up until end of October so I pulled the unit and took it to them with the hopes that it would be a quick swap of the new unit, but unfortunately there was enough debris to damage the pinion gear so that all has to be replaced as well. I went with the same replacement LSD thinking this was a one-off but I guess not. I’m a bit pissed at Eaton for misleading me in believing that this True Trac was a tough unit. I’ve already paid for the new one so I’m stuck with it. The helical cut gears in my True Trac were completely sheared in half. While it only had a 1 year warranty I am still having a discussion with Eaton regarding this issue. I used non-synthetic 80w-90 gear oil as they suggested, changed the oil a couple times and always checked my oil level regularly. No reason yours or mine should have done this. When I recover from this repair I will replace the new True Trac altogether and will never recommend the unit to anyone. Thanks for sharing your story. I’ll update when I get pics from my diff shop.

 

Unfortunate. I’ve been running one in my 3rd gen for a little over a year and I too noticed the fluid looked a little glittery after the first drain. It’s just stock 3:90 gear ratio and 32s. I absolutely love the performance of the unit though so I’m praying mine lasts a long time, however with this post and also the way I beat on it, my confidence has definitely been lowered

 

I’d say to just keep an eye on it. I only saw glittery oil as well until I opened it up. I found small metal chunks exactly like to one in the original post of this string. I have to say that it did really well when I was on the forest service roads last summer while building a Client’s house. I even pulled a loaded F250 up a steep hill out of a snow bank and it was amazing. Hope yours gives you many happy years of service.

 

BTW, the Ford owner was none too happy when he had to be rescued by a Tacoma. I think he said something about buying a Tacoma.

 

I had a Z28 with the factory "Torsen" diff (this is a Torsen variant) and it took literally hundreds of high HP starts and never failed. Ripped the splines off more than a few hokey GM axle shafts (happens when you use sticky oversize F1 tires). What I see in the pictures is a lot of secondary damage due to the hard broken material being circulated in the housing. That broken material probably came from the end tips of the helical teeth being brittle. Common industrial gearing practice is that these are made of AISI 9310 or 4320 - heat treated by carburizing. This looks like a heat treatment process error. Properly done - it works.

I spent a few years working as a field engineer for Xtek - the originator of the carburizing heat treatment process (initial patents a hundred years ago). What I don't see on the helical parts is a couple of design features common to heavy duty industrial transmissions. The end tooth tips would be radiused back - to protect from "burning" the exposed end tips to glass. And the teeth would be "relieved" to make the high loads occur deeper into the the face of the tooth. The tooling doing the tooth generation is "plunged" a few thousandths at the ends of the teeth to force the loading as they engage, out into the tooth enough to protect the ends. This sort of thing is typical of the work done to protect a $650,000 mining machine transmission - but unfortunately not Eaton's diff.