I've had a TrueTrac in my rear diff for about 25,000 miles. Recently the rear diff started making some strange clunking noises primarily when coasting in a low speed turn, like negotiating a parking lot. I spent a lot of time inspecting it on jack stands and eventually confirmed it was due to some backlash in when the unit is differentiating -- not backlash in the ring & pinion but between the two side gears.
Now the TT ought to have some backlash since it is geartrain but the noise had me worried. Some googling brought up horror stories of TT carrier bolts backing out and causing diffs to blow up. It seems Eaton remedied this more than 10 years ago by changing from cast parts to machined and utilizing fine thread screws. But I was unwilling to take the chance that this noise might be a bolt falling out!
So, out it came.
Everything looks beautiful... 4.56 gears had been set up by Zuk back in October and were pristine. Pinion preload still felt good. No worries for the R&P or bearings.
Plugged the axle shafts in to see if I could replicate it by hand. Nope. It was a fun experiment though.
Time to dig into the TT unit. I made a diff holding bracket with some thick plywood.
**Before tearing into it I confirmed that all 12 bolts holding the TT unit together were tight and none were backing out. So the problem is not loose bolts but something else**
Unbolted the four 17mm headed bearing cap bolts and the carrier with ring gear still attached came out. Popped out the six 3/8-24" (7/8" long) bolts and took one side of the carrier off. Kind of a pain with the bearing still installed -- you can see in the image how the bolt wants to interfere with the bearing. Side gear remains installed in the second picture.
One of the spiral gears removed. Very little wear is evident.
Side gear looks good too
So the surgical inspection did not reveal anything strange. I repeated the process with the opposite side and found the same story. Since the bolts had to come out I took the opportunity to upgrade them. There was enough thread depth to allow a 1" rather than a 7/8" screw. These 12 point "grade 9" bolts (similar to ARP) have a 170ksi strength vs. 150ksi for grade 8.
Torquing to 45 ft-lb was a trick due to interference from the carrier bearing. I adapted a wrench to be my crows-foot and adjusted the setting on the torque wrench to match. Bolts went in with red loctite
When reinstalling it I decided to try out the LubeLocker reusable gasket rather than FIPG. So far so good on leaks.