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Shop rebuilt front differential failed on first test drive, trying to figure out why?


NAXJA Forum User
Recently decided to open the wallet and pay for a 3.5" lift, 4:10 gears and lockers on both axles of my 99XJ. Today I got a call from the shop doing the work that I should come in so we could "talk". * I get there and the first thing I see is the front diff open on a lift with destroyed brand new Eaton E-locker inside. *Deep strike marks all the way around the circumference of the locker where the pinion had been driven into it. *So yeah, not good. *Obviously they are going to redo the whole thing at their expense, but what worries me is that the explanation for the failure doesn't make sense to me so I thought I would run the scenario by y'all to see if you have any ideas about what happened?

Background: *I brought the jeep in with a dana 30 front axle, a 1" transfer case drop, and new a stock height crossmember they were supposed to replace but didn't for reasons nobody can explain to me. *It had a cheap a 2" rusty lift and adjustable LCA's from a previous owner. *Wasn't planning on replacing the uppers because I thought I didn't need to.

So, I get there today and they tell me that because the transfer case was dropped, and the lift pulled the front axle back, there wasn't enough room for the stock drive shaft which they said they struggled to install and then when the put it on the ground and test drove it, the flex of the suspension drove the front drive shaft and the pinion into the locker and ring gear. *Setting aside the fact that they just said they installed a fully compressed front drive shaft (I'm a bolt on monkey and even I wouldn't do that) does this explanation make any sense?

I've called the most respected custom jeep shop in our area and they told me there is no way that would happen with a 3.5" lift and a 1" t-case drop. * Also, even if they did install a fully compressed front drive shaft when they set it on the floor wouldn't the LCAs extend the driveshaft?, not shorten it? *Could they have just not fully seated the input yoke? *But if that was the case, there would have been no preload on the pinion bearing right? *I can't image even the worst gear guy not checking pinion preload. *I'm trying to figure out how this happened so it doesn't happen again when they finish the 2nd rebuild. * Any ideas what could have happened here? *Should I trust these guys to do another gear job? *They already did the back axle so I feel like I'm stuck with that install.
Defective install. I am using the factory original front driveshaft that fit with a 2" budget boost, fit with a 3.5 RE lift, and still fits with 5.5" of lift and control arm drop brackets.

Lifted or not, stock control arms will put the axle in the same location.

Have them re-do the install and leave the driveshaft un-installed. If it doesn't blow up again after a few hundred miles, install the driveshaft and check the available compression and extension of the splined slip yoke.
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I totally agree. A t-case drop will make a negligible difference in distance of the t-case to the front axle, and any lift puts the front axle further way from the t-case. Even if the shop test flexed the front suspension, a stock front driveshaft will not bottom out in length with the setup you describe.

The shop definitely did something wrong, but hard to imagine what. I'm thinking that there is no way to push the pinion shaft forward without destroying the case, unless there was something fundamentally wrong with the pinion shaft install as you suggested. I recommend that after the shop removes the damaged stuff from the diff that you have them document the inside of the diff case to show no damage to the case itself. In addition, if the driveshaft did bottom out (or didn't compress due to some kind of screw-up), the driveshaft and the t-case should be destroyed, or at least damaged, as well, so it should be kinda obvious if they really did somehow bottom out the front driveshaft.

The problem with completing the work at this shop is the concern for quality and what happens down the road. You put yourself in a situation where you have to let them put everything back together and then leave it untouched for a period of time. If you have the shop perform only a partial reassembly, e.g., leave out the front driveshaft, and then you install it yourself later and the diff starts howling or the driveshaft vibrates, then they'll blame it on you. You'll need to thoroughly test drive it after you get it back, preferably with a shop employee in the vehicle. And try to get an extended warranty.
Someone left the pinion nut loose, and it opened up, losing preload on the bearings and allowing the pinion to move.

This is why every diff I do, gets a BRAND NEW stover but, and a borderline amount of red loctite (not the no-name stuff the gear companies ship with the install kits).

Everyone makes mistakes, and shit does happen. It’s a good sign that they are fixing it, but it’s a bad thing that they are blaming the driveshaft length. Frankly they reinstalled it in post gear install. It’s on them.

I’d be asking for a new set of pinion bearings. This is why shops charge so much for gear work. They have to be ready to go back in there a second time when needed.

Good luck!