Rear Diff

[Scout1067]

Well, I was happy today that I decided to go ahead and buy the new diff cover for my rear diff. My jeep has been godawful loud since I got it two months ago and I figured that the diff was just low on oil and/or had serious gear grinding issues but I would not know until I got it open.
I have the AMC20 on my jeep and when looking around for parts I found a complete new cover on Autozone with gasket so bought it since it was only $30. I finally got it up on the lift yesterday and am sure glad I got the cover. The old cover was bent at the top, it almost looked like somebody had tried to pry it open with a screwdriver but I don't know how they would do that since there is not much room up there. The oil that came out was super thin, almost like 3in1 oil, there was water in it, it was low, and the inside of the gearbox had some surface rust on it. The gears themselves look pretty good so that was a relief, I was afraid I was going to have to replace the gears and pinions.

I used brake cleaner to spray the inside out and get all the contaminated oil out of the gearbox. Took me two cans until the brake cleaner was coming out clean.

Then I let is sit for a half hour for the break cleaner to dry before putting the new gaskets and cover one. As a side bar, anyone know where I can get a new filler hole plug for the AMC20 , I haven't been able to find one on all the usual sites. Mine was rusted in and i had to heat it to get it loose. The threads are pretty tore up on it but I think it will hold for now.
I finally got it all cleaned up and the new gasket on and it looks pretty good. Biggest thing though is that on the drive home it no longer makes the horrid noise when driving.
Next job is to service the tranny and transfer. Here is what it looks like now.

 

[jp360cj]

Nice work. I don't recall the size, but the fill plug is just an NPT pipe plug that you can get at the hardware store.

 

[Lumpy Grits]

Drive it for a spell and then drain the fluid again.
Check the back-lash and do a pattern check.
I'd be concerted about the bearings, way more than the gear teeth.
Hope you checked the front diff too.
What about the tranny and t'case oil?
LG

 

[Scout1067]

Drive it for a spell and then drain the fluid again.
Check the back-lash and do a pattern check.
I'd be concerted about the bearings, way more than the gear teeth.
Hope you checked the front diff too.
What about the tranny and t'case oil?
LG

I did the front diff as well. It looked good with clean oil and no rust on the inside. I was planning on putting a couple thousand miles on it and then changing out the diff oil again. My thought is that driving with the clean oil will clean a bunch of that surface rust off and if i leave it in it will tear up the gears by itself. Since a new bearing kit only runs $AMC 150 or so I will probably replace the bearings when I do the oil next time just to be on the safe side.

I am going to try and get the tranny and transfer oil changed in the next few weeks but that depends as it won't be moving much after next week, because I am having surgery and will out six for six weeks while my neck heals up.

 

[Torxhead]

Your differentials, tranny, and Transfer Case should all have vent tubes coming up from them for deep water crossings. Which could be how the water got in there in the first place.

 

[BIG4D]

I have to tell you, I would be concerned about the amount of rust pitting on the gears. If the gears look like that the bearings might as well.
It’s not an easy job, but it might be worth it to pull the carrier and check the carrier bearings and races. If there is ANY pitting, they need to be replaced. Pitting will cause the hardened face of the bearings to start flaking off. Once this happens, they get loose and take out the gears. Not to mention the noise.


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[Scout1067]

I have to tell you, I would be concerned about the amount of rust pitting on the gears. If the gears look like that the bearings might as well.
It’s not an easy job, but it might be worth it to pull the carrier and check the carrier bearings and races. If there is ANY pitting, they need to be replaced. Pitting will cause the hardened face of the bearings to start flaking off. Once this happens, they get loose and take out the gears. Not to mention the noise.


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Thanks, I hadn't thought of that. I had a pretty strong magnet in the flow when I drained it and got zero shavings so my thought was that the pitting wasn't a major problem. I was going to reinspect them when i drain it in a few months and then go from there.

I get it now now how Jeeps turn into money vacuums. I am also starting to think it might have been cheaper to just start doing heroin.

 

[BIG4D]

Well, unlike heroin, a Jeep won’t land you in jail, but it might put you in the poor house!
Unlike heroin, the only tracks you will end up with will be in the mud! Lol!


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