Issues installing new gears

[JKCuda]

So...I'm installing a Dr. Diff rear diff and 3.55 gears in my 741 case and I'm having a hell of a time with this pinion. Getting the depth and preload set has been a real PITA as it's the first time I'm doing this, but that's not really my problem. The problem is constantly having to tighten and remove the pinion nut is absolutely destroying the threads on the end of the pinion. Is this normal? I know these nuts are tighter at the end so they have some sort of locking tension it's to the point where I'm not comfortable continuing.

With that being said, I've tried a thread chaser which helped, but it's still not very optimal. I have a extra set of 3.73's here that I tried the nut on and I can hand thread it to about 1/8 of the end of the nut. On the bad one I can't get it any closer than about 1/2" by hand. Are re-tapping these threads viable or would that remove too much material to let the nut "lock" properly? Or should I start with a new ring and pinion again and buy a castle style nut with no taper to do the test fitting?

Any tips are appreciated...

[Dmod1974]

If you're still in the process of getting a good pattern dialed in and setting pinion depth, you shouldn't even be installing the crush sleeve or cranking that nut down hard yet.  Install it without the sleeve and seal and tighten the nut just enough to take up any slop; the pinion should still spin with light resistance.

Get a new nut for the final assembly; they're one time use as far as I'm concerned.  You'll never crush the sleeve down without stripping an already damaged pinion nut.  Hell, I've stripped brand new aftermarket pinion nuts before getting the sleeve crushed down on other make differentials.   If the pinion threads are damaged you can try chasing them, but again, you may be screwed when you try to crush the sleeve down requiring you to start over.

The pinion nuts are lock nuts, but if you're damaging the threads are you sure you have the right size and pitch nut?

[JKCuda]

If you're still in the process of getting a good pattern dialed in and setting pinion depth, you shouldn't even be installing the crush sleeve or cranking that nut down hard yet.  Install it without the sleeve and seal and tighten the nut just enough to take up any slop; the pinion should still spin with light resistance.

Get a new nut for the final assembly; they're one time use as far as I'm concerned.  You'll never crush the sleeve down without stripping an already damaged pinion nut.  Hell, I've stripped brand new aftermarket pinion nuts before getting the sleeve crushed down on other make differentials.   If the pinion threads are damaged you can try chasing them, but again, you may be screwed when you try to crush the sleeve down requiring you to start over.

The pinion nuts are lock nuts, but if you're damaging the threads are you sure you have the right size and pitch nut?

I have a nut that I was going to keep for final assembly, no issue there.  How exactly am I supposed to get the preload right though without tightening the nut down?  I wasn't torquing it to the 240 ft/lbs, just tight with a Kobalt impact.  Hell that's the only way I could get it on.  As far as being the right one...it's what came with the kit from Dr Diff and I ordered 2 more from Summit that are motive(same as my gears), 7/8-14, and I'm having the exact same issue.  I'm more concerned with the fact that the threads on the pinion are taking damage vs the nut but based on what I've experienced so far I don't see how I could've avoided it.  Something isn't right though, that's for sure.
 

[Dmod1974]

You don't need preload set to measure pinion depth and backlash.  You just can't have any play in it.

[JKCuda]

I understand that.  But even to get it tight enough to take the slop out it was producing shavings and messing up the last 3 threads on the end which is why I'm in the predicament I'm in.

[Dmod1974]

Earlier you stated you were trying to set depth and preload and constantly tightening the nut on and off destroying the threads, so I assumed you were setting preload and cranking it down.....

If the pinion is badly damaged, you'll need to replace it.  That's not normal either way, so either something was up with the nut, or the pinion threads.  Always oil the threads too.  In my experience, the nut is the fusible link and will strip before the pinion.

[JKCuda]

Gotcha, yeah sorry, just meant I was in the process of doing everything.  Was just installing the nut tight, not torquing.

I hate to do it, but this is a full resto and I've got a shitload of money wrapped up in this thing, so I think I'm gonna bite the bullet and order a new ring and pinion so it's done right.  I do not like the idea of re-cutting threads on something like this.  I have some splicer nuts coming from Summit as well so we'll see if they are any better.

Appreciate your help.

[Dmod1974]

Yeah, it sucks, but better now than when it self disassembles later on.

If you are doing any performance driving with that car, I'd highly recommend a solid spacer kit.  It's a little more set up work and may not be 100% necessary for your build, but you won't need a 10ft pipe to crush anything down, and it will hold preload until the bearings where out, instead of possibly during hard launches.  You can just torque it to like 200lbs or whatever they call for and be done.  It also makes future pinion seal or yoke changes a breeze without having to worry about marking the nut or under/over crushing the sleeve.

You may want to consider making some pinion set up bearings as well.  It saves a lot of time in the long run during set up.

Also, I've ordered rebuild kits for the 8 3/4" before and gotten TWO pinion nuts in the kit.  One will fit, and one did not.  The right one should hand thread on until it hits the egg shaped end threads that self lock the nut.

[JKCuda]

Yeah, it sucks, but better now than when it self disassembles later on.

If you are doing any performance driving with that car, I'd highly recommend a solid spacer kit.  It's a little more set up work and may not be 100% necessary for your build, but you won't need a 10ft pipe to crush anything down, and it will hold preload until the bearings where out, instead of possibly during hard launches.  You can just torque it to like 200lbs or whatever they call for and be done.  It also makes future pinion seal or yoke changes a breeze without having to worry about marking the nut or under/over crushing the sleeve.

You may want to consider making some pinion set up bearings as well.  It saves a lot of time in the long run during set up.

Also, I've ordered rebuild kits for the 8 3/4" before and gotten TWO pinion nuts in the kit.  One will fit, and one did not.  The right one should hand thread on until it hits the egg shaped end threads that self lock the nut.

Yeah I made one for the inner bearing but I need to do it for the outer.  To be fair, I was "pressing" the outer bearing on each time using the tightening action from the nut which probably caused my issues to begin with now that I really think about it.  I'll be making a bearing for that one as well now.  My kit came with 2 as well, 1 for the 29 spline and 1 for the 10 spline which did not fit.  I have some 3.73's here that I decided not to use and the nuts hand thread on to those until it hits those threads you mentioned, about 1/8" from the face of the nut.

Again, really appreciate the tips!

[JKCuda]

Also, I do already have the solid spacer too.  It was already in there from the previous owner(s).

[ignition1]

When initially setting pinion depth I use a NON-self locking nut. Just a regular straight threaded nut. Fortunately I have a few various big nuts around that I use for the initial setup on different pinion threads. When the pinion depth and pattern check out to where I want it, then I switch over to the new self-locking nut to set final preload.

You can run a tap through the nut too cut out the crimp, but I found it doesn't really cut it all the way out and you still need just a little bit more than hand strength to get it on and off. To purchase a tap that large is probably more expensive than just buying a dedicated plain straight cut nut for your pinion thread. A normal nut will spin on and off with just fingers and makes the set up less annoying after the 5th time

[70 Challenger Lover]

How about using a standard hardware store nut to get everything how you want it instead of the lock nut? Those lock nuts are very hard on threads.

[JKCuda]

Yeah I found some regular nuts on Amazon. Everything is here now, gonna put it together tomorrow.

[JKCuda]

This is with a .009 shim under the bearing. No shims is too shallow and unfortunately 009 is the thinnest dr diff supplied me with. What's everyone think of this pattern?  I wouldn't mind trying .004 or so but I don't have one. Don't even know if they make one...

[ignition1]

I would try for a better pattern. I don't like the sharp points of the pattern, I like a more ovalish pattern, even it is a little high or low, but not pointy.

What is you back lash set to at the moment?