Differential - Rebuild or not?

[Ryan_M]

Is there any way to tell whether a differential needs to be rebuilt without actually tearing the thing apart? Since I have the axles out and knuckles off I might as well do it now if it needs to happen. With that said, if it isn't necessary I'd rather not do it. I read through the service manual instructions and my head immediately started throbbing. Quick reviews of rebuild threads made me feel a little better but not much.

My front differential is pretty gross but I don't see any obvious damage. I can't see the bearings and seals. Am to assume they're shot just due to age alone? If I don't pull it apart now are there gradual warning signs once it starts to go bad or does the thing just grenade in a shower of twisted metal and gear oil?

I have the same question about the rear differential.

[garage gnome]

Only reason it would need rebuilding is if there is metal in the oil or there are chipped teeth. I've never had to tear into one.

[Carls_jeep]

From what I can see in the photo it looks ok to me.

[Jeff_M]

They tend to make a lot of noise if they're going bad, and yours are quiet.  I'd button 'em up and run 'em. 

[athawk11]

Ryan,
I agree with the others.� Spin the gears by hand.� If no broken teeth on gears, no grinding sound from the bearings, you're probably just fine.� If inner seals are bad, you can spot gear oil in the axle tubes with a flashlight.� If it's just grease in the tubes, your seals are fine. Button it back up and call it good.

I will add... For insurance and since you have it open, just make sure bearing cap bolts and the bolts holding the large gear to the carrier are torqued to spec.

Tim

[Ryan_M]

Very encouraging news guys, thanks for the help.

[Ryan_M]

Ok, so I dodged a bullet on the front diff but now I'm around to the back and have a new question.

Everything looks good - no metal flakes or broken teeth. My concern is with the spider gear pictured just above my fingernail. I can slide it up and down an 1/8", maybe even a 1/4". Doesn't seem like it should have that much play but I can't find anything to confirm that.

What say you great greasy minds?

[F Bill]

That seems excessive, can we see a picture without a finger, closer if you can?

[Ryan_M]

Tough to get good pics in there. You can see a washer on top of the gear. I think there's supposed to be a conical thrust washer there right? This doesn't look conical but I can't see enough of it to tell.





I am including a video too. It's blurry but it at least shows the amount of play.

[media]http://www.youtube.com/watch?v=WRxwQ1_FtJk&feature=youtu.be[/media]

[F Bill]

Was there a metallic cast to the gear lube when you drained the axle?

It almost looks as if someone left out a thrust washer when they assembled it. I think but am not certain you can remove the spider gears without removing the carrier....might be worth a better look. Centrifugal force will push the gears into a better mesh as the axle gets up to speed. I don't like the way they mesh when still.

[Ryan_M]

I didn't really see a metallic cast to the gear oil. If it was there it was very very slight...and trust me, I was looking for one. I actually drove the first 300 miles after my original vehicle overhaul with NO GEAR OIL in the rear diff. I drained it during the tear-down and for whatever reason (distracted by a phone call, probably) it never got topped off. Months later I finished the Jeep and off I went. The front was full, the rear was dry aside from whatever residual stuff was left clinging to the gears. It's a wonder it didn't weld it self together and grenade.

[athawk11]

Ryan,
Do the two larger spider gears have movement inward or outward?  If so, the washers on the back side of the larger gears may be missing, allowing them slip outward and increasing the gap between the smaller spider gears.  I can see the washers on the small gear.  I can't see them on the big gears.

Just a guess really.

Tim

[Ryan_M]

Do the two larger spider gears have movement inward or outward?

No movement in the larger spider gears or the small bottom one.

[Ryan_M]

Heck with it. I've pulled it apart. Conical washers were there but something is still amiss. See '51 3A project thread for progress.

[Bruce_W]

  It looks to me like there's a lot of wear on the side (bigger) gear teeth, and on the differential pinion (smaller, or "spider") gear teeth too. Due to the tapered shape, as they wear, the pinions can move toward the center. Movement of the side gears may be limited by the pinion shaft (cross pin) or the center axle spacer. It also looks like the spacer has been moving on the pin. The only way that can happen is for the pin to be loose in the case, or the side gears are moving in the case, taking the axles and spacer with them. For this to happen, there must be a lot of wear on the side gears where they ride in the case, and also in the holes in the case where the side gears run. Gravity is taking up the play between the lower pinion and side gears by pulling the side gears toward the pinion.
  There's been a lot of wheel-spin going on here, I'll betcha.

  Now, to avoid confusion, even tho I've tried to use the proper terms, everywhere I've written "pinion", say "spider".      BW