Now moving on to my other dilemma, yep there's more........told you this has been a month from hell.....
Last week driving to work I went past a sound barrier on the freeway and thought I heard a noise that I thought sounded like a slight exhaust leak (ticking). My first thought was that there was a rice rocket passing me with a fart can on it but that turned out not the be the case.
During the drive home that afternoon it got slowly worse. I pulled the Jeep into the shop when I arrived home and tried crawling around under it but couldn't detect anything resembling an exhaust leak. Revving it up loaded and unloaded, it didn't seem to change things. My son stopped by to check on me and was less than pleased with me when I was out in the shop crawling around under the Jeep. I told him it sounded like an exhaust leak but not like an exhaust leak, more of a ticking or similar noise but I promised him I'd take a look at it at a later date and I'd go in the house.
So, rather than piss him or my wife off, I closed up the shop and figured I get to it when I was feeling better and I would just drive the truck to work.
Well late last week I finally got around to diagnosing the Jeep and after a test drive I determined it was not an exhaust leak and after a bit of side streets making turns and acceleration/deceleration hits, I could feel it in the floorboards so that confirmed it was NOT an exhaust leak but something was going on in the drivetrain. A friend of mine blew his transfer case up last fall in his Jeep and he described the symptoms very similar right before it split the case in half. I crawled around under the Jeep on Saturday and found nothing out of the ordinary. I put it on jackstands and let it run in forward and reverse at idle and could ever so slightly detect a small knocking sound with the stethoscope in the rear differential.
I thought this was odd as I hadn't been "hot-rodding" the Jeep since we returned from the Swell trip. Even during our trip to the Swell, I hadn't really pushed the Jeep as most of the off-roading we did was merely scenic drives and I had been driving the Jeep around town and freeway for 400-500 miles after returning from that trip.
Well I racked the Jeep and pulled the rear diff cover to find bits and pieces. The oil still looked like golden honey since I replaced it in August before our Ouray, CO trip. It didn't have any sparklies in it, just a couple of rather large pieces. My first thought was maybe something in the carrier itself because it wasn't consistent and seemed to increase in noise during turns, which indicated maybe a side gear or spider gear in the locker/carrier assembly.
A close examination when I removed the cover showed very, very little damage to the ring gear. Only a few indentations were discovered where I figured pieces were jammed into the teeth but nothing like a normal ring gear failure. I examined my spec's that I had engraved in the ring gear from 2018 when I rebuilt it last. I double checked rotating torques, which had lowered a bit but is completely normal after bearings take a set but the backlash was still dead nuts on where I set it up 49k miles ago. The gears now had 49k driven miles and approx. 17k flat-towed miles and I know I don't beat on my Jeep so I was dumbfounded.
After spreading the case, removing the carrier with the ring gear and examining it on the bench I really couldn't see anything jump out at me. Until....I went to remove the pinion gear. That's when I realized that is where the large piece came from.
I removed the pinion gear and found the large piece was a tooth from the pinion gear but it didn't fail like a normal pinion failure, it looks like it was much deeper than even the flank of the pinion gear tooth where I normally see them fail. This one was down well into the root of the pinion and it was more than the one tooth. It appears to be about 4 of the 9 teeth affected.
Jeep racked, axles removed and ready to spread the case and remove the carrier assembly.
Large piece of pinion tooth stuck to the dipstick magnet and a slightly smaller piece lying on the bottom of the differential.
For the most part the ring gear looks great. Wear pattern looks fantastic with only a few small indentations or dings in the teeth but nothing like a normal ring gear failure. There was this very small piece between the carrier and the ring gear which lead me to think maybe the carrier internals had failed such as a spider gear or side gear.
Checking backlash and comparing to the spec's from 2018.
Still right at the same spec as when I set this configuration up with the 4.56 gears after coming from the 5.38 gears.
Here you can see the failure at the root of the teeth and in multiple places, not just one tooth failed.
In this picture if you look closely you can see the two damaged teeth just above the missing tooth and then very hard to see but you can see a small crack in the next tooth above those and follow it down into the flank of the teeth which lead right up under the bearing surface.
My thinking is maybe, just maybe this was a manufacturer's defect where it could have been over heat treated and made to be too brittle down into the root of the pinion. Generally when ring/pinions are heat treated and ground, they are brought up to a mid-60's RC at the surface but the root of the part is not hardened to that degree to allow some "give" or "flex" in the root of the tooth.
In my racing days I have seen guys destroy ring and pinions on hard launches but they break the teeth right down at the flank of the tooth which then allows the pinion to eat the ring gear almost instantly but I have not seen one break this far down into the root, below the flank of the pinion teeth before.
I had my son look at the parts when they came over for Sunday dinner and he made an observation compared to the new pinion I had sitting on the bench. He said if you look at the small radius under the bearing of the old pinion it appears to be more of a ridge whereas the new pinion I had sitting there had a nice smooth radius under the bearing, where the pinion shim would reside. I'm just wondering if this could be something more related to a manufacturer's process or defect and less of a failure based on my driving.
IF I had allowed the Jeep to begin hopping on an obstacle or had been breaking the tires loose on the pavement and then they grabbed, maybe I could determine I caused the breakage based on driving behavior but that isn't the case.
This one has me scratching my head on why it failed.
Then to make matters worse, I grabbed my trusty old Snap-on bronze hammer that I have had for over 30-years and when I was driving the pinion out of the axle housing the handle broke apart in multiple pieces as well as the area cracked between the two bronze surfaces. ****! That was the first Snap-on hammer I had ever purchased back shortly after starting my career and now it's destroyed as well.
Thanks for looking and for allowing me to vent on the events of the past month.
