Pinion failure analysis

wvracer821

wvracer821

Well-known member
Joined
May 27, 2020
Member Number
1546
Messages
1,016
Loc
Morgantown, WV
Finally tore down the front axle in my daily driver 2018 Ram 2500 because of a noise that pointed me towards the driver side carrier bearing but found much more than just a bad bearing. Several pinion teeth are chipped and the ring gear certainly has some odd wear from chewing on metal. For reference, this is a Chrysler 9.25 front axle found in 2014+ Ram HD trucks. It has an axle disconnect coupler on the passenger side so in theory the ring and pinion are not spinning while in 2wd. I put these 4.56 Yukon gears in a while back when I went to a 37” tire roughly 55k miles ago and the front always made a little bit of noise in 4wd at higher speeds but I chocked it up to “aftermarket gears made in China”. Over time I started to get some more noise up front even in 2wd. I could hear it when rotating the driver side tire in the garage. I don’t use 4wd much in this one, I can’t remember shock loading it outside of normal use case, it’s never been airborne or anything like that. I’m trying to wrap my head around what happened to it. At this point I feel like I just got a bad gear set.

Here are 2 pics from my initial install years ago. 0.035” pinion depth (OEM shim) and backlash in the 0.006-0.010 spec. It’s really tough to get any kind of carrier preload on these because it uses side adjusters like a 14 bolt.
IMG_6441.jpeg

IMG_6442.jpeg


Here are the pics of the chipped up pinion I took out a few days ago

IMG_6396.jpeg
IMG_6397.jpeg
IMG_6398.jpeg
IMG_6399.jpeg


After placing my order Friday for a new set of gears I finally ran a pattern last night and here is where I’m at currently. Same 0.035 pinion depth and 0.007” backlash. I’m going to play with it a little bit today and see if I can make it any better. I’m going to add 0.003” more to the pinion first.


IMG_6460.jpeg


IMG_6459.jpeg


I’m no gear setup pro or anything but it’s also not my first one. I’ve done probably a dozen of them or so over the last 10 years.

Any ideas from the brain trust here?
 
Is it a high or low pinion?
I know know these axles.

If it's a LP running backwards, the pattern on the drive side (normal coast) looks a little off towards the outside of the teeth to me.
 
Pattern looks good (even used).

I'm thinking poor QC on the part of the bearing. If you're sure the fluid was good, topped off, and full of unicorn farts --- then we can potentially eliminate that possibility. Poor gear quality is a possibility, but I believe movement from the bearings exposed the issue.

Was does your pinion angle look like? Super high HP and/or aggressive driving? Could have some housing flex (becoming more of a problem as manufacturers chase down that last .023 mpg of fuel economy.

Even with the disconnect, it's still spinning centrifugally --- which is not a bad thing as long as fluid levels and oils are good.


My final opinion? Yukon gears and housing flex.
 
Bebop said:
Is it a high or low pinion?
I know know these axles.

If it's a LP running backwards, the pattern on the drive side (normal coast) looks a little off towards the outside of the teeth to me.
Click to expand...
High pinion, reverse rotation
 
Bebop said:
If it's a LP running backwards, the pattern on the drive side (normal coast) looks a little off towards the outside of the teeth to me.
Click to expand...

In my experience .... running towards the heel is almost irrelevant. Running off the heel is another story. :laughing:

I'm always more concerned with crown/root than I am with heel/toe.
 
EndlessMtnFab said:
Pattern looks good (even used).

I'm thinking poor QC on the part of the bearing. If you're sure the fluid was good, topped off, and full of unicorn farts --- then we can potentially eliminate that possibility. Poor gear quality is a possibility, but I believe movement from the bearings exposed the issue.

Was does your pinion angle look like? Super high HP and/or aggressive driving? Could have some housing flex (becoming more of a problem as manufacturers chase down that last .023 mpg of fuel economy.

Even with the disconnect, it's still spinning centrifugally --- which is not a bad thing as long as fluid levels and oils are good.


My final opinion? Yukon gears and housing flex.
Click to expand...
Stock pinion angle, only 1” of lift on the truck.
 
That really looks like something went through it. Was the shrapnel match up with the divots? Was there extra shrapnel? Check the tubes?
 
bdkw1 said:
That really looks like something went through it. Was the shrapnel match up with the divots? Was there extra shrapnel? Check the tubes?
Click to expand...
There was a few chunks. Looks like most of it got chewed up in the oil.
 
Do you guys not measure pinion depth in the housing and adjust shims based off that?
 
Grind down an air hammer chisel to fit in there and use that to preload it.
 
TrailTamer said:
I don’t think it’s an option on fronts as there’s the seal in the way.
Click to expand...
My mind went right to ChryCo 9.25


The picture clued me in that I was thinking of the wrong axle. The older style ... you could have still accessed with a long extension and a homemade socket/nut. But that's another discussion, right? :)
 
After 7 changes I got it put back together with as much preload as I could get with a long skinny punch. Let’s hope it holds up this time. Final pattern is a little bit deep but backlash is in the tight end of spec at 0.006 and honestly I’m tired of messing with it.
IMG_6467.jpeg
IMG_6468.jpeg
 
You must log in or register to reply here.
Top Back Refresh