Planetary gears' axle showing some concerning wear

good morning all,

on Saturday I dug into my differential. I was looking to assess and replace carrier bearings, but they really seemed fine. They assembly rotated smoothly and freely and made no sounds at all while  the assembly rotated. So in the end I decided to leave the bearings well enough alone, but during my inspection I noticed some strange wearing on the planetary gears' axle, aka cross pin (picture below).

 I like to think my spatial reasoning is decent but I have to admit I'm having a hard time imagining the gears in my head and how the wearing in the image below would occur. The wear is only on the side shown which is opposite the retaining pin hole. When I asked another internet forum one user suggested this was because the pumpkin itself was bad. They went on to suggest that when changing between drive and reverse I probably heard/felt a banging. We'll I didn't drive this truck too long before I started working on it so I can't say for sure, but certainly nothing like that jumped out to  me. Also, it's a manual transmission, so I'm not sure how much that changes this diagnosis.



At any rate, I replaced the gears' axle/cross pin (as well as the retaining pin which was extremely stubborn to get out the first time). And I think at the moment I'm going to reassemble the whole thing and press onward. And if it gets real bad and I HAVE to replace the pumpkin, which pretty much means the whole axle, I might go so far as to install an aftermarket limited slip differential. But, you know, baby steps.

MY ACTUAL QUESTIONS:
1) How did this wear happen?
2) How long will it last before I have to do something, and what would need to be replaced? I'm basically putting off addressing the root cause of this wear, but how long can I reasonably let it go?
3) With a new gears' axle installed, what will the tell tale signs that its wearing again like this last one (pictured above)?



As always thank you for your help!

Usually that kind of wear is caused by one wheel spinning while the other is stationary. It could be worse, son had the differential in his 1986 Plymouth Turismo 2.2 spin and then spit the gear shaft out through the side of the transaxle case.

this was my first thought also. a differential barely knows any wear causing movement until it is allowed to  work as a "differential". when it's all evenly balanced the carrier only spins in the bearings. so only the bearings are moving. I'm curious as to what year trac loc this is. I know that the early versions had the small pin. and the later versions had the larger size pins which is why you must have the correct year axle shafts too. the larger pin provided greater load carrying surface for the spider gears.

This absolutely makes all the sense in the world. I have no idea why I wasn't able to imagine the gears working like this (like they're supposed to). The axle *should* be original - from a 1985 F150 4WD. I can't speak to the specific trac loc vintage but it's likely whatever OEM version came with the truck. I replaced both of the axle shafts through Rockauto and I'm installing them this weekend, I guess I have to trust that they are right size for this.

So it sounds like what I'm hearing here is that this isn't an issue with the pumpkin like I was led to believe just maybe someone getting froggy with it at some point in it's lifetime.

well, I realized that I assumed it to be a trac loc being in a 4wd and I may be wrong. I have seen 4wd with open diffs. but a 4wd should be trac lock. so, if it is an open differential, it's easy to see how one could have been spun excessively, possibly at an angle that starved the carrier of oil. but if it really is a trac loc NOW is the time to replace the clutches and center spring. possibly a great time to convert to trac loc if it is not.

So bear with me, I'm still learning a lot... After doing some research I think it actually IS an open differential. Which, no, does not make a lot of sense for a 4WD.



I have really gone back and forth on switching out the differential. The main reason I'm not doing it right now is because I understand it to be quite onerous getting the shims all correct and frankly I have not found a YouTube video that explains it well enough. It would be pretty disastrous to get it wrong. However, if you have any resources at all, I'm happy to check them out. because getting a locking differential in there would make me a lot more comfortable about taking this thing on a forest service road.

Also, I'm working my way towards the front and the transmission is DEFINITELY on the list. Do you have any recommendations on clutch kits. it will be my first time trading one out.

that looks to be an open diff. I do not see the clutch recess nor the tabs. true setting up a different carrier can be a finicky task. especially if you are nervous about it. there is another option but I'm not sure that I would recommend it for a truck mostly driven on the street. a mini spool! it is a set of blocks that replace the spider gears and are held in place by the pin and locks the two axles together. many of us have used them well in off road vehicles. I even tried one in my flareside but pulled it after two weeks. with a good running 5.0 and a wide ratio aod through 3.73 gears, it was hard to keep it strait. wanted to get sideways at every chance. fun, but when it did a 180 when I was not even trying it had to come out. I like "getting loose" to be on demand not out of control.

If you lived near NE Oklahoma, I know where there's an 87 with an 8.8, 3.55-geared limited slip rear, complete.  He wants a couple hundred for the whole enchilada, and I was going to buy it and swap it into mine (which is nearly exactly what you have - down to the year, and open rear).  I opted to go with a 9" LS out of an 81 Bronco, as I'm just stubborn, and like the 9" Ford rears.  Swapping an entire rear end would almost be easier (to me) than converting an open to a limited slip.  

I think you are completely right, it would be a WHOLE lot easier to buy an entire axle with a limited slip instead of swapping out the gears.

I AM curious about the 87 rear that you were tracking. Do you have any more info on it?

Was/is behind an 87 half ton that was severely wrecked in front; the T18 I'm swapping into mine is from that truck, and I was considering the axle as well until I ran into the 9".  Silicone around the cover tells me that someone has been in it - may be a good or bad thing, but probably to pull the axles at some point for some reason or another (axle bearings/seals?).  The trans also had similar silicone around the top cover, and the internals on that T18 look pretty good, so was possibly maintained well.  Private owner has it in a field behind his house.

I did essentially what you are talking about on Darth, but I had a damaged bearing tube on the left side that I had to replace the seal every year before inspection due to the damaged area. I also wanted a limited slip 3.55 to replace my open 3.55 gear.

I had purchased a 1990 F250 parts truck, 460, E4OD and 3.55 traction loc, unfortunately, since Darth is a DRW truck, the axles are different. I bought a DRW axle with an open 4.10 gear and found it had some water damage to the gears which wasn't a problem. I transferred the innards of the SRW 1990 axle into the DRW housing and in doing so discovered Ford had increased the width of the rear brakes from 2.5" on the 1986 F350 to 3" on the 1990 F250 and to 3.5" on the 1993 F350 DRW axle.

I kept the 1993 3.5" wide brakes for Darth.