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Rear axle swap

Rear axle swap
T

thistle3585

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1979 Jeep CJ5 with '72 304 V8, MC2100carb,T150 trans, AMC20 rear diff with locker, Dana 30 front diff, Dana 20 Tr Case, Procomp Springs, Gabriel Ultra shocks.
I took my Jeep to a friend, who is a mechanic, to look at some issues and he told me that my rear differential was about shot. He said that without pulling the cover off he guessed that there were some broken teeth along with some other issues. The grease seals were also shot and leaking grease in to the brakes and it also was in dire need of an alignment. We decided that I'd probably be better off simply swapping out a whole new rear end since I needed to also replace the springs and do some welding on the frame. I could do all that at one time. Can anyone give me any tips on selecting a new rear end. I'd like to stay with the stock setup, but am a little leery about pulling one from a junk yard and just having the same problem. This is one thing I have no knowledge about but I'd like to try and do this myself.
 
Did you drive the Jeep to your friend? If your missing teeth on a ring or pinion gear the Jeep usually won't do anything but make terrible noises when you try and move it.

Do the right thing and pull the cover (only takes a few minutes) and take a look at the bearings and gears.

If you decide to swap axles you need one from a 1976 - 1981 CJ (for an exact swap - be sure that the axles are the original narrow track), and it has to have the same gear ratio as you are currently are running.
 
Do the right thing and pull the cover (only takes a few minutes) and take a look at the bearings and gears.
Click to expand...
Your mechanic friend should have removed the cover. He seems to have pulled your tires and drums off. I wouldn't be happy with an rear axle swap unles I knew it was rebuilt/ had new seals anyway.

30+ years on a boneyard axle is to much a risk, at least for the seals. At that point, you'd have taken apart the entire thing anyway. Rebuild it if this is the case.

Confirm you have the stock axle and springs, before you go part-hunting.

There may be some numbers on the cover flange of the axle. Write them down. :)
 
I originally took it in for him to look at the brakes and he didn't charge me to do that and I didn't think it fair to tie up his lift when he had other cars waiting. I'll pull the cover this weekend and see what is going on. The problem is that I have no idea what I am looking for.
 
Don't worry, if it's broken, you'll know it when you see it.
I figure it's always better to fix your own stuff then to buy someone else's problems.
 
Well when you take off the cover you'll know if youve got broken teeth by the "plop(s)" in the drain pan. ;) Look for metal shavings as well. If you dont see anything post a pic here after you take off the cover.
 
I agree with everyone in that I would rebuild what you have rather than have to rebuild one fron the junk yard. Unless your tubes are bent.
If the teeth are broken or chiped it will be easy to see, even if you don't know what your look'n at.
 
If you have extra parts in the axle housing it will be pretty apparent as a general rule. Drain the axle pull the cover and fish around in the bottom of the housing, if there is any "shrapnel" that is where it will collect. :D

As far as building an axle yourself? I would say no, setting up an AMC20 is a pretty fair size job and requires a few special tools. You should be able to find a specialist in axles to supply the labor and experience for about $250 and you just supply the parts or tell him what you want.:cool:
 
Pull the cover x how ever many. bad or broken teeth are easy to find. The seals leaking are an easy fix. The problem with junk yard axles are they normally need new seals, bearings and gears. The only real reason to get a set of junk yard axles if your diff is not cracked or your tubes are not bent is to upgrade to a better set. I would open the cover and see what shape the gears are in. If they are bad have your stock one rebuilt and add in new 1 piece shafts. IF you need a ring and pinion nows the time to upgrade to a lower set if your running bigger tires.

either way good luck
 
Broken teeth can happen different ways, though. On the fairly stout AMC ring and pinion set it seems that the breakage is often due to the classic M20 axle bending that allows the pinion and ring gears to move out of a good contact patch and leads to breakage. Replacing the R&P without addressing the other issue often leads to another broken gear set and the " that dang mechanic messed up my install" rant.
 
I got the cover off this morning and posted photos of it on my website at Jeep I wasn't sure how to post them here, plus you can increase the size to see detail. Anyhow, there doesn't seem to be anything broken but there does seem to be a weird wear pattern on the gears. The outside of the teeth on the rack and pinion(?) have some rust and no wear. I think you can easily see that from the photos. So, I am wondering if my axle is bent. How would I determine that? Also, is this an AMC20 rear end? Also, unfortunately the oil coming out of it looked like chocolate milk.

Also, as an aside. If anyone is in and around southern Indiana and would be willing to spend an hour or two with a newbie going over this Jeep I'd be very grateful. Steak and beer? :)
 
Well, the good news is nothing is broken, and the PO installed a lunch-box locker.

The bad news is that you have rust damage from that 'chocolate milk' that was in the diff. The rust / milk is caused by water in your gear lube. All that water rusted the ring and pinion and most likely ruined the bearings. You may be able to use the R&P for years but if you do, it will probably be very noisy if it doesn't fail.

IMO, you need a new R&P and all the bearings.
 
Your friend may have heard some ratcheting and popping when he was looking at the axle. Looks like you have a Lunchbox style locker installed, that would definitely give you some ratcheting sounds. Rust looks like there was some standing water in the housing for some time with the oil floating on top. Doubt the whole axle is shot, but with the water issue, could probably use some new bearings. I'd clean everything inside best I could, put the cover back on and new oil, see if that helps.
 
Thanks. I really haven't had any problem with it at all, and didn't hear anything while driving it, but the guy looking at the brakes heard some noise while turning the wheels. So, am I okay to clean it out, reassemble and refill with lubricant and go about my way and keep an eye on it or is this something that needs immediate attention?

I'm wondering if replacing the R&P and bearings is something that I am capable of doing? I'm mechanically inclined but I have never done anything like this before. What would I be looking at to have this work done?
 
I would just change the fluid and drive it for a while. If you have any leaks change those seals as well. Then do a visual check at a later date, If it makes noise, then you may have to do a rebuild.

As for changing the bearings, you need a press and torque wrench as a bare minimum and really need a dial indicator to check the final assembly.

Oh yea, forgot to add in my previous post, you have an AMC20 . See this thread for Jeep CJ axles. -->> http://www.jeep-cj.com/forums/f105/cj-axles-12186/
 
Looks drivable to me, Until you get around to replacing the bearings/seals, but do make that a priority, above any (fun) stuff you want to do to it. id fill it with the heaviest gear oil you can find. A boneyard axle is usually in the same condition at best.

check the axle vent, too.

And lockers can be a little hard to get used to, with the noise and tightness while turning.
 
Thanks to all. A couple questions before final assembly.

Use RTV with the seal?
Is 80W-90 oil sufficient?
What would the torque on the screws be?
 
80/90 should be fine, I always use a thin film of RVT and for torque... I just use my calibrated elbow / arm torque wrench. :) The cover just needs to tight enough to maintain a seal so there are no fluid leaks. , just don't over tighten and force the gasket out. I'm sure someone may know the FSM torque - but not me! :chug:
 
the trick to covers like the rear is to cross tighten , evenly. super tight is not a great thing in this case but an even seal is.:D
 
Good score on the locker. When ever you jack up one side and spin the tires you will feel the locker popping and racheting. The first time you hear it or feel it happen it will make you :dung: your pants if you don't know yOu have a locker. I would just re-seal it and run it that way. As far as the seals go i would install one peice axles and new seals. The one piece axles will help you from braking the 2pc axle shafts that came stock, but if the PO installed the locker he should have known about the shaft problem.. Did you say you already have 1pc shafts? If so you got a decent set up.. If not get em and you'll enjoy the jeep. Enjoy it.
 
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