Hi all,

A few weeks ago, I took my truck in to the dealer to have a leaky pinion shaft seal replaced under the 7/70 warranty, which they did (see my post https://www.dieseltruckresource.com/...d.php?t=161608). Curiously, they replaced the whole pinion shaft as well. I didn't question it at the time (but maybe I should have, because aren't those pinions and crown gears matched sets??). Well then the other day the differential croaked the first time I put it into 4WD, resulting in lots of popping, clunking and whining. So back in to the dealer it went.

I got a voicemail this afternoon that the dealer is completely refurbishing the front differential and "ordering a lot of parts." So, my guess is that either because the pinion was not matched with the crown gear, or more likely the pinion was not seated at the correct alignment depth (probably wasn't re-shimmed for proper backlash) that the front diff just tore itself to bits. Anyway, they're covering everything of course, but here's my concern:

Rebuilding a differential requires lots of precision measurement and adjustment. If these guys had issues seating the pinion shaft correctly the first time (and didn't know to install matching pinion and crown gear sets) then how can I trust that they can completely rebuild my front differential? I would feel much better if they were just replacing the entire front axle assembly as a complete unit with a new, factory-assembled unit. What do you guys think? When I call tomorrow morning, should I push them to replace the whole assembly? I really don't want to deal with possibly another failure.

 

The pinion gear shaft comes with the ring gear as a matched set. I don't think you can get a pinion separate. I wonder why they would have had to replace the shaft for a seal leak, the seal rides on the yoke, not the shaft. I wonder if the pinion nut came loose when you stuck it in 4WD? Do they have the parts they used the last time listed on your invoice?

 

Yes they are a matched set.
But I have never heard of them replacing the pinon for a leaky seal, many many times they have to replace the yoke as its grooved.
depending on what broke/wore out is the only way to tell what happened.

You can push all you want for a complete housing rebuilt fresh, but AAM does not sell them to dodge like that, (for warr. work) so it won't happen.
If you are that leary of their work, once it done, take it to a rear end shop to have it looked at.

 

Once you get it back you can take the cover off and check the backlash and gear pattern to see if it was done right. Also the rotating force is a good measurement of preload on the bearings. Not real hard to check any of those either.

 

I went back to check my previous invoice and you guys are right, it was the pinion yoke, not the pinion itself that was replaced. So, is it possible that the pinion nut was not properly torqued and that caused the failure? Looking at the service procedure, it calls for the hub bearings and axle shafts to be removed in order to measure correct torque. I'm guessing there's a good chance the dealer was in a hurry and neglected this part of the procedure, so proper torque wasn't achieved. So the first time I put it in 4WD, that play at the pinion was too loose and it chewed things up.

 

That would be my guess.
9 out 10 times you can reset the pinion bearing preload with out tearing down the whole axle.
Sounds like the tech that did yours struck out

 

the AAM pinion has a a crush sleeve so if you do not properly set pinion preload you have to remove the pinion put a new crush sleeve, if you left the the axle shafts in and set total preload it would just spin real easy, but pinion preload would still be established.
more likely an answer is that you need special tools to pull the yoke off and to put the yoke back on, i have seen many techs strip the treads of the yoke.

 

Actually the yoke is splined. The pinion is threaded along with the nut, but I'm confused as to what they are actually stripping on the yoke? Are they stripping the mounting flange bolts?

 

Just an update...

I finally got my truck back after 2 weeks at the dealer. The front diff was completely rebuilt. Here is the cause of the failure that's stated on the invoice:

CAUSE: PINION NUT FAILED BACKED OFF CAUSING PINION DAMAGE AND CASE ASSEMBLY DAMAGED

2 5086689AA BEARING-DIFFERENTIAL SIDE
1 5086691AA DISC-DIFFERENTIAL
1 5086717AB GEAR PKG-RING AND PINION
4 5102232AA LUBRICANT
1 5086688AA BEARING-DRIVE PINION
1 5086690AA BEARING-DRIVE PINION

No charge to me, all warrantied. And to think, all this due to a simple oil leak fix that they botched the first time.