I redid my pinion seal on my 8.25 and I just cranked the bolt back down. Long story short, after a couple hours the differential made an awful grinding noise and I must have sicked a bearing. After a few tries of re-torquing it without success I bought another 8.25 at a junk yard and am in the process of installing it. This one also has a pinion seal leak. I would ignore it in fear of ruining another differential, however the yolk is very rusted so I need to switch it with the one from my original axle. So I have to make sure I do this right. I am going to:

Take a base reading of the bearing pre-load with the wheels and drum off. It should be around 10-15lbs.
Mark the yolk and the bolt, and count the thread rotations.
After installing the new pinion and yolk, re-install the nut with blue loctite to the exact thread rotation count as before, and take another preload reading.

So my questions are:
Pre-load is defined as the amount of torque it takes to spin the bearing, correct?
Should I tighten the nut slightly more than last time?
If the final pre-load reading is below spect, 10-15 ft/lb, should I tighten it more?

I really can't afford to mess this up. I appreciate any advice. Thanks

 

Measure the existing pre-load first. If you're swapping yokes, there is no guarantee that the nut will end up in the exact same place. Replacement axle has the same gear ratio right?

 

The measurement is in.lbs.

At 10-15 ft.lbs. it'll do exactly what it did.

 

The gear ratio is the same, yes. The original yoke is pitted pretty badly, do you think I could just clean it up an keep running it? Also, what do you mean by exiting preload? Sorry

 

What does the book say? Usually setting the pinion pre-load is the amount of rotational tension (in In/Lbs) on the pinion only. No gears or axles. I redid my Jeep's a long time ago, that's what I recall. Correct me if I'm wrong.

If you're just replacing the pinion seal and nothing else, and you know or assume it was fine before, what I generally do is torque a new nut on to about 100 ft lbs (by hand with a torque wrench). You could probably peen down the old nut too...but the recommendations are for a new nut (I've done both). And you should have (or make) a tool out of steel bar, which attaches to the end of the pinion to hold it from rotating. It takes quite a bit more torque to crush the crush-sleeve, so 90-100 ft/lbs usually does the trick. YMMV. A lot of manuals don't publish a torque list for re-tightning a pinion after a seal replacement (to cover their butt). But I ran across a GM FSM a long time ago that did.

If you need to set your pinion's torque from fresh, you could verify it first. Or get a new crush sleeve & nut ...remove all the gears and start over. At that point you might as well replace the bearings too. Then follow the book on tightening the nut and crush sleeve to the proper amount.

Torque hack: Since very few people have an in/lbs torque wrench that's accurate down at real low in/lbs, I can suggest if you took a 1/4" or 3/8" drive socket with something like a 3/8" deep well chrome socket (not an impact socket), a socket about 5/8" OD. Then grab the 'clean' deep-well socket with your clean, dry hand as hard as you possibly can and rotate the ratchet ...and take note of the torque you are applying as you rotate it. The amount of torque at the ratchet handle will be about 18 in/lbs. I doubt you can hold it anymore than 20 in/lbs...even if it hurts and tears your hand as you squeeze it. But if you squeeze to the point where it doesn't quite hurt ...that'll be 15-16 in/lbs. Sorry if that's confusing, but...it gives you a guide. Put a 9/16 socket and you can probably hold it up to ~30 in/lbs of squeezing. Plus or minus a bit.

 

Torque Hack 2 ; Using a $5 electronic luggage/fish scale, one makes a lever a measured distance long, and rotates the pinion nut while reading the toque on the scale, do some maths

Its quite accurate,

the rotating pre-load is usually about 75% of the breakaway torque

 

Good info here! I've got to replace my front axle seal. I've watched numerous vids on people doing the mark and remove and re-install to same mark technique. I've also heard the 100ft lbs should put you in the range IF re-using old crush sleeve.

 

I think the D30 is set with shims, so it's less critical to get the torque right.

 

Strange I've read both...lol...guess I'l find out.

edit...Found this comment "LOW pinion D30s have a crush sleeve. HP's do NOT."