Pinion Nut Won't Stay Tight (8.8 Rear Diff)

[Innocent Fool]

2003 FX4 Level 2 with 8.8, 31 spline rear diff. having trouble with the pinion nut backing out.

Almost looks like oil is running past the threads of the nut causing it to come loose (?)
Tried putting black RTV on the pinion threads and back of nut before torquing down, Worked for a short time but happened again.
Tried putting an O-ring over the pinion shaft and torquing down which helped the longest but still same issue.

Continuing to have issues with the pinion nut loosening up causing play in the pinion which takes out the pinion seal.
Have replaced the seal 3 times and in the last 8000 miles and it just happened again.
All times nut was torqued to spec with torque wrench.

Is there some secret to keeping the pinion nuts tight?

 

[scotts90ranger]

The pinion nut is supposed to be replaced every use, it's a lock nut, you would be better off cleaning everything off with a wire brush on a drill or something (nothing sticks to silicone) and use some red loctite

 

[ericbphoto]

I agree. Remove pinion nut. Replace seal again. Make sure everything is super clean. Apply red Loc-tite to new pinion nut and torque properly.

Do NOT install an o-ring between the pinion nut and the flange. This must be a solid connection to maintain bearing preload.

If this problem persists, it may be best to have the differential disassembled, check the bearings and gears and re-assemble with new crush sleeve making sure that the whole setup is right.

Here are some instructions from Yukon Gear pertaining to this assembly.

 

[Roert42]

Forget what I said, was thinking about new vs used bearings not crush sleeves.

 

[Roert42]

Are you pulling the carrier out every time to set the preload?

You should be, and if your not your torque is going to be wrong.


You could probably just get away with a new nut with locktight, but you should probably replace the crush sleeve and set the bearing preload all up from scratch like eric said.

 

[Innocent Fool]

Thanks to everyone for the info on this.

Have been replacing the seal and reusing the nut without issue on several other vehicles but this is the 1st one causing problems.
Haven't been pulling the carrier to set preload so torque is likely not 100%, but there's only so much I can do on the street

Will replace the nut with a new one and see how that goes.

Thanks again.

 

[Roert42]

Haven't been pulling the carrier to set preload so torque is likely not 100%, but there's only so much I can do on the street

If you are not pulling the carrier to set the preload, how are you doing it?

It is set by measuring the Torque needed to turn the pinion and bearing. Should be somewhere around 20 Inch/lbs. Going to be hard to get an accurate measurement when trying to turn the whole axle and everything.

 

[19Walt93]

I set the preload by feel but I've been building rear ends since about 1975. I can feel the preload in the small amount of movement allowed by the backlash. If you aren't sure, a little too tight is better than a little too loose. Replacing the nut isn't mandatory if you thoroughly clean the threads and use lock-tite.