Topic: Whats wrong with my 3rd?

[82rustbeast]

I pulled out my third to find out why my truck lurches in 4wd and I found that the rear is a 4.37, and I think the front is a 4.10, its and 82 truck so the 4.37 was put in. Anyway, when I pulled out the rear 3rd, I noticed some gouges in my diff, can anybody tell me what happened and if it is safe to use this diff to install my new 5.29 gears on.

[Duffil]

those marks are from the pinion "walking" into the diff.  check your crush sleeve and pinion bearings.  It could be from a PO.

My front carrier has that, but not quite as deep as yours.  fine to use.

[93tonkatoy]

The damage to the carrier is caused by the pinion being drawn into the ring gear. Either the pinion bearings were allowing movement (in and out), or the carrier bearings were loose allowing the carrier to be drawn toward the pinion. The grooves are cut by the end of the pinion gears as they make contact. In this condition, in 2wd, it would have made a whining, and grinding sound when decelerating, and possibly also while accelerating. If it was  quiet (in 2wd) before you pulled it, then I would say that it was old damage. (before the 4.37 was installed)

If the grooves are very deep, I would personally NOT use that carrier, as that is the structural "cage" that keeps everything in the diff together and aligned. If the grooves are less than 1/16" deep, I would probably go ahead and use it, and plan to find a better one later. It would really be a personal choice: thickness of material/ depth of gouges and how hard you wheel. for street use, probably would never have any issues; for full-on rock brawling, good possibility of it letting you down. Assuming that it was not whining and grinding, you should be able to judge by the stress you put it under before you knew of the damage, as to what amount of stress it has already taken

Also, check the "flat" area on the face of the teeth on the ring gear and the pinion. The flat area should be a uniform width from one end of the tooth to the other.

edit: Duffil beat me to it, but makes a good suggestion. If you decide to use it, run it in the front axle.

[82rustbeast [OP]]

I think that it was just a full 4.37 3rd diff from an 81, but the gouges were just in the thediff, not the carrier casing. I havnt ever heard any whining or griding noises, but Ive only driven the truck for a month and a half since I got it going.


I still havnt seen the front one yet. Hopefully its not the same way   

[Duffil]

I think that it was just a full 4.37 3rd diff from an 81, but the gouges were just in the thediff, not the carrier casing. I havnt ever heard any whining or griding noises, but Ive only driven the truck for a month and a half since I got it going.


I still havnt seen the front one yet. Hopefully its not the same way   

the part that is grooved is actually called the carrier. 

[82rustbeast [OP]]

oh I thought the carrier was another word for the housing.

[LOL @ IFS]

I think that it was just a full 4.37 3rd diff from an 81,

'81s were only available with 3.90 gears.  And I wouldn't use the diff.  Why chance it?  You're going to be in there with the gears anyway, why not do it right while you're there.  Trail failure sucks for everyone because they either have to tow you out, or spend hours helping you fix it on the trail.  If you're not going to fix it right yourself, fix it right for the other guys.

[82rustbeast [OP]]

well whatever year the 4.37s came in, I guess I need to find another diff. What about a lockright? The truck is a DD and it sees moderate trail use. 

[93tonkatoy]

While you are in there, I would go ahead and have a good look at the splines on the axles. If the carrier bearings were what allowed the damage to the carrier, it could have caused significant wear to the splines.

[LOL @ IFS]

well whatever year the 4.37s came in, I guess I need to find another diff. What about a lockright? The truck is a DD and it sees moderate trail use. 

Any of the auto lockers will do you well if the truck sees moderate trail use.  I figure I'll throw this out there- I'll have a pair of 3.90 3rds for sale dirt cheap in about two months, located at Hill AFB in UT. 

[RN37DD]

i have a few 4.10 3rd's that the carrier was chewed on, and was going to throw them in the scrap pile, until i found a builder that was just calling it cosmedic damage. i think he was putting together a 5.29 and i though that would be causing more stress the a little 4.10. they were rough to turn, the pinion nut was loose. tightened them up and it turns smooth.