2021 Mojave - rear-end replacement, spider gear broken

[brianbishop]

Hello,

I took delivery of this in June 2021 and drove it 6K miles before swapping the 33" tires for 35" BFGs. At some point in the last year (miles 24K - 36K) it started sporadically failing to shift reasonably. As I accelerated from 5MPH to say 40MPH it revved higher and higher without shifting. Then I'd take my foot off the gas and it would eventually (within 5-20 seconds) shift up. Didn't happen every day, but maybe once a week.

Took it the the dealer a month ago at 36,350 miles and they said they heard a noise in the pumpkin. It took a month to get the parts in and do the repair, but they say the rear-end had metal shavings in it, and the spider gear was broken. Thank goodness the $7K bill was zero due to the warranty.

Does this have to do with the up-sizing of the tires? Anyone ever seen/heard of this before?

Thanks!

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[BearFootSam]

While 35’s do put more stress on the drivetrain, the JT is purportedly package protected for 35’s indicating that with 4.10’s one should be able to run them without any concern. You weren’t bouncing around with the diff locked were you?

 

[brianbishop]

While 35’s do put more stress on the drivetrain, the JT is purportedly package protected for 35’s indicating that with 4.10’s one should be able to run them without any concern. You weren’t bouncing around with the diff locked were you?

Thanks for the reply. I admittedly have not locked the diff except for under very limited test circumstances.

 

[Lunentucker]

35's should be no problem at all on Dana 44's with 4.10 gearing.

 

[JeepOfTheseus]

Any chance they took pics? I'm no expert, but wouldn't "broken spider gears" be kind of an all-or-nothing failure?

 

[brianbishop]

Any chance they took pics? I'm no expert, but wouldn't "broken spider gears" be kind of an all-or-nothing failure?

I will ask the dealer, great idea.

 

[jac04]

IMO, I don't think your erratic transmission shifting had anything to do with the rear differential. There are times that the transmission will 'hold' a gear for longer than expected, notably when you are accelerating briskly and abruptly get off the throttle and then back on it without accelerating. The transmission seems to expect that you will want to accelerate rapidly again, so it holds the lower gear until it senses that you just want to maintain current speed.

The Tru-Lok rear diff with the e-locker is fairly robust. I would be curious to see pictures of what the dealership found.

 

[Wheelin98TJ]

Any chance they took pics? I'm no expert, but wouldn't "broken spider gears" be kind of an all-or-nothing failure?

I don't think they sell spider gears separately for the Dana Advantek Tru-Lok locker.

 

[JeepOfTheseus]

I don't think they sell spider gears separately for the Dana Advantek Tru-Lok locker.

I guess what I mean is...how could a "broken spider gear" be a very sporadic failure, where it works most of the time (once a week is not very often), but then occasionally leads to (of all things) shifting woes. Shifting sounds more like a clutch or electronic/sensor issue. The fact that he was gaining speed is even more odd...I know the system will go nuts if it detects unexpected driveshaft/wheel speed, but that didn't sound like the case here. Is it maybe testing for torque as well, and getting unexpected readings due to the weakened gears?

Not strictly questioning anything, just trying to learn how it correlates.

 

[Wheelin98TJ]

I guess what I mean is...how could a "broken spider gear" be a very sporadic failure, where it works most of the time (once a week is not very often), but then occasionally leads to (of all things) shifting woes. Shifting sounds more like a clutch or electronic/sensor issue. The fact that he was gaining speed is even more odd...I know the system will go nuts if it detects unexpected driveshaft/wheel speed, but that didn't sound like the case here. Is it maybe testing for torque as well, and getting unexpected readings due to the weakened gears?

Not strictly questioning anything, just trying to learn how it correlates.

That part has me puzzled. I don't think the broken spider gears have anything to do with the transmission not shifting properly.

 

[brianbishop]

I feel the same way about the RE repair not correlating with the transmission's symptom. I expect to see that shifting issue again - a friend of mine suggested it could be due to the fact that I put 35s on and didn't tune it for the larger tires.

The repair had a 'milking the OEM for warranty work' vibe to it...

The repair included the entire rear end, not just the spider gear, FYI. And a pair of shafts that emerge from the pumpkin (?) which the dealer didn't know weren't included in the rear-end assembly, necessitating another few days of waiting before they started the repair.

Thanks for all the input here, folks.

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