When installing new yokes on the axle for an aftermarket driveshaft, it is s.o.p to determine the preload of the bearing with an inch-lb torqe device. How critical is it to get this spot on. I found some published books about this topic and they stressed the importance of this.

 

You take a in-lb torsion wrench, with the wheels off, and turn the wrench until the pinion rotates, and measure this in-lb. Do this a few times and take an average. Then you take off the nut, put on a new yoke and torque the nut somwhere between 150-200ft lb until you reach the same preload on the bearing. Everyones torque value may be different.

 

Since the JK axles use crush sleeves to preload the bearings, which is relieved when the pinion nut is removed, this preload must be put back on the bearings when the yoke and nut are reinstalled.

The preload is measured in in-lbs like you mentioned and is a measure of how easily the pinion gear (only) rotates on it's bearings. This resistance is small and is measured in in-lbs. The differential and axles add alot more resistance making it fairly inaccurate to measure the pinion preload only. In the second pic, there's no pumpkin in the housing, like in pic 3.

Too much preload on the pinion bearing adds heat and reduced pinion bearing life, because its very tight, but too little is much worse. The ring gear is trying to push the pinion gear away from it whenever they turn and the force grows as more power and wheel weight and size are added.



If there's not enough preload, the pinion will deflect and bad things can happen.

A standard impact will not add enough torque to put adequate preload on the pinion bearing. A large cheater bar and means to hold the flange may be needed like in pic 1.

 

I just installed an Adams rear driveshaft and replaced a pinion seal in the process. I bought an in-lb beam torque wrench with a gazillion adapters and got a reading of 12.5 in lbs to begin movement, 10 in lbs to maintain movement while the axles rotate forward. Reverse yielded numbers 2.5 in lb less. Whatever- wrote it down and kept going

when I installed the same pinion nut I did it with hand tools- my electric impact is a beast but unwieldy so I held the yoke with a wrench and torqued- I jumped in increments but was getting the same preload as before until I struggled to get the nut to 160 ft lbs.

i then thought I over torqued- as I was getting rotational readings of 20-30 in lbs. I realized that my pinion would still turn for only 10 in lbs about 1-2 rotations clockwise or counter clockwise- any further rotation yielded higher torque needs, as if drag was increasing despite no brakes on the hub.

i set it at 160 ft lbs and kept going- I’m somewhat comfortable with that, but am afraid about the eventual drag I was experiencing- is that normal if the axle shafts are still in? Should I have torqued more? I went a little bit past my original index mark on the nut and pinion. I don’t want to put her on the road if there’s going to be problems. Any help is appreciated!

 

Murdoc -- what you've done is completely acceptable IMO. outside of breaking down the entire axle, you're never going to get a good read on pinion preload. What you have done is what we all do when we have to change a seal. 160 ft lbs gets that sucker on there good again, and is not risking you affecting the crush sleeve anymore as it takes much more force that that. I wouldn't overthink it.

 

thanks for the sanity check- I think I’m going to get a shirt that says “hold on, let me overthink this” - I wasn’t happy with bending the rim of the seal and my grease application so I went it again and re-did it. I will say the RR distributed seal without the pre-set RTV allows for an easy install even with adding black silicone.

I tried to set the torque higher and it would get higher by a few in-lbs, I would spin the yoke again a couple of times and it would go back down. I think the variance is caused by initial friction from the seal. I torqued up every 5 ft-lbs to 190 and left it. Thanks again for the reply!