A friend and I did it in his shop. (He owns a body shop).

In the past, I've had good results the hairy-chested man's way:

(Barring any extreme science - sorry KelVarnson) tighten the nut just until there is no slop in the pinion bearings, and then just a little more (less than 1/4 turn). It's hard to get it perfect with the ring gear in the way. I realize you want some preload on the bearings, but not much. If done right, it should have just a little resistance when turning by hand. With the ring gear in, though, it is hard to gauge the resistance you have - and as you know, it's something that can only best be experienced, not described.

(That's how I've done it in the past. But, in this case, we cheated).

We just used some white-out to mark the position of the nut and counted the threads. When it went back on, we just tightened it to the same position. We also used white-out to mark the position of the spline and the u-joints. If anything, there might be a bit too much slop.

Since I re-used the pinion bearings this method was even more appropriate as there's essentially none (or very little) bearing preload needed. As for the pinion nut itself, it just needs as much gorilla as you can apply. If I checked the manual, I'm sure it'd say something like 300 ft/lbs or so. With a breaker bar and a "helper" bar, I'd say I'm in the neighborhood.

(Hope you weren't expecting high-tech).

later . . .

 

OK, I am officially a geek. I looked up a few things in my copy of Mark's Standard Handbook for Mechanical Engineers. They give a pretty thorough treatment to the effects of rolling resistance and air resistance, and the combined effect of the two on power needed to drive a car. To make a long story short, they say that for a "large car", the horsepower requirements at the driving wheels would be 50 horsepower at 70 miles per hour, and 100 hp at 95 mph. I think our trucks are bigger than what they would consider to be a "large car", both in terms of weight and frontal area. So it might be safe to assume that 75 horsepower could be required to drive our Superduties at 70 mph.

Unfortunately, the section of the handbook dealing with differentials didn't say anything about efficiency. Maybe someone knows where to find that kind of info. I'd be surprised if they are more than 98% efficient, but that is just a guess, please correct me if you find data showing otherwise. Assuming 98% efficiency with 75 hp, the power dissipated by the differential would be just a little over a kilowatt. A kilowatt is the number commonly bandied about as the typical requirement to power an average home, so that kinda puts things in perspective. After reading all of this, it doesn't surprise me to hear that a temperature rise of over 100 degrees occurs. It's a good thing that a differential housing has a continuous stream of fresh air blowing across it when it's called upon to do its heaviest work.

Desertrefugee, thanks for the tips on setting the preload, that's something I've always been a-scared to mess with (guess my chest isn't hairy enough :-) ) But, in the larger scheme of things, I would think that the amount of heat generated by even the worst case of over-tightened bearings would pale in comparison to the heat due to loss in the gears. Then again, that is just another S.W.A.G. on my part, and I've probably contributed more than my share of those to this thread today, so I'll shut up for a while.

 

Which is definitely NOT something my truck gets in southern Arizona in the summer - or coming down through California's Central Valley last summer with the outside temperature hanging between 110 and 120 all the way from San Jose to Valencia!

 

Yeah.... you need to see a shrink about this....... (just kidding). I do know that it is an option in semis to have 'front-rear' and 'rear-rear' axle temp gauges. The temps are usually 100-150 deg F.