AMC 20 issues?

[thiswontbetooexpensive]

Hello Jeep-CJ community. I have a question about the AMC20 rear differential. Was wondering if it was Limited slip, so i put a jack under the differential housing and got the tires off the ground with the Transmission in neutral. Spin driver rear wheel clockwise and the passenger rear wheel turned counter-clockwise. This means Limited slip from some other posts i have searched.

Problem was that the passenger rear wheel was not turning as fast as the driver rear that I was spinning. I changed sided of the vehicle, and spun the passenger side. The driver side remained stationary. didn't matter which way i spun the passenger side, driver didn't move. I had plans to take the diff cover off to inspect and change fluid, but I don't know what to look for other than metal shavings. Please provide assistance as to what I need to look for. Pictures of good and bad would be helpful. As i have previously stated, i drove the vehicle 20 miles before disassembly. After returning home, i felt the drive train for excessive heat and nothing seemed even overly warm. (i did check all fluid levels before the trip)

Thanks in advance for the assistance.

 

[thiswontbetooexpensive]

UPDATE:
Code on diff housing is A. Best as I can tell, I was mistaken earlier and this is not a trac loc due to the fact that the wheels spun in opposite directions. Now this is verified by the code on the outside. (other sources say this was for 3.54 gears and open diff for narrow track axles)

I'm pretty sure that both wheels should spin regardless. To expedite the repair of this, what should I look for in terms of what to dismantle and also what to look for in the process? Is this the common problem with the two piece axles that is remedied by changing to one piece?

 

[Saddle Tramp]

The AMC20 as you know comes with a two piece axle, a shaft and a hub (the hub is the part with the wheel studs). The hub is attached to the axle shaft with a large nut and a key that fits into a slot in the shaft and the hub to keep the hub from turning on the shaft. The problem is the nut tends loosen up with time and when it does the key will shear off allowing the shaft to spin freely inside the hub rendering the axle useless as far as propulsion is concerned (dead in the water so to speak) and this can happen in the Wally World parking lot just as easily as on the trail. So, if your jeep rolls down the road under its own power in two wheel drive without problems then most likely the axles is fine.

The base design of the free spooling rear end distributes power to the axle (side) that offers the least resistance, assuming you have an open diff in your jeep then I’m not sure just what you plan to fix unless it is to change out the two piece shafts if you have them. Check for the two piece axles by looking at the center of the hub for a large nut. If no nut you are in the clear.

I don’t remember what you said you were going to use the jeep for but if hard wheeling is on tap then you may want to consider upgrading to a Dana 44 as the CJ AMC20 has more problems than their two piece shafts such as a weak housing and axle thin tubes.

 

[gert]

you have an open diff. if it had a Limited slip or locker both wheels would turn the same dirrection. if you want to re test it only jack one side up and try to spin the wheel(tranny in neutral) if it wont spin then you have a Limited slip or locker in it. if it does spin then you have an open diff. if you are driving it and still have an I6 in your jeep a set of one peice axles and some type of locker will work for a long time. If you put in a V8 and wheel it hard it will eventually break.i had a lockright in mine which I had a lot of fun with, however it can get squirly in the rain, a Limited slip like the auburn units work great on road but not as well off road

 

[PaRenegade]

you may want to consider upgrading to a Dana 44 as the CJ AMC20 has more problems than their two piece shafts such as a weak housing and axle thin tubes.

However the other two issues are minor once the 1 pc. axles are added. A couple welds around the tubes and add a truss and you should be fine. Some say at that point your better off than a stock 44 due to the beefier gears in the AMC20 .
You can improve a stock 20 much cheaper than finding a 44 and having it reworked to fit. Finding one all ready to swap from an end of run 86 CJ7 is like finding a needle in a haystack.

 

[thiswontbetooexpensive]

Thanks for the input. Looking at some one piece shafts now. When talking Of welding the tube, are you referring to the entire circumference where the tube enters the diff housing, or just fill in the holes about 3 o'clock and 9 o'clock looking at it from the back? Those are welded up now and looks more recent than the axel manufacture.


This won't be too expensive Dear! That's what I keep saying. Over and over again.

 

[heff]

Too bad you`re so far away, I`m just getting ready to part my Jeep out. I have Danna 44 Scout axles. Never got to upgrading the front but the rear one has a Detroit locker w/513 gear. One piece axles should take care of any breakage problems though. Good Luck!

 

[Tommy]

Just a thought but you might recheck the numbers on the differential to make sure it isn't Limited slip. If the clutches are bad or the wrong fluid is in it, it will not act like a Limited slip but in fact the wheels can turn in opposite directions or not at all like you saw. Taking the cover off will also leave no doubt.

Tommy

 

[thiswontbetooexpensive]

View attachment 12304This is what I found when I took the cover off today. No metal shavings just stinky gear oil. Doesn't have any water in it.

Checked ring gear numbers and the 3.54 math works out for gear ratio. It was driving before I strowed it all over my garage, axle is still held in place. ( I can't just pull it out anyway with the wheels still on). I will update after some further investigation. Thanks for the help.
Is anyone driving toward Houston or Dallas from Michigan anytime soon with room for Dana 44 axles?


This won't be too expensive Dear! That's what I keep saying. Over and over again.

 

[PaRenegade]

When talking Of welding the tube, are you referring to the entire circumference where the tube enters the diff housing, or just fill in the holes about 3 o'clock and 9 o'clock looking at it from the back? Those are welded up now and looks more recent than the axel manufacture.

No, it's referring to just putting (3) 1"-1.5" long welds around the circumference where the tubes join the center section. From what I've read, a continuous weld around it would limit any movement such as expansion and contraction, since they are two different metals, which may lead to a crack in the joint.

 

[Saddle Tramp]

Thiswontbetooexpnsive’s jeep is a 1980 so it is narrow track; try finding a Dana 44 out of a 1972 to 1975 CJ or 1972, 73 Commando. They are 30 spline axles that will bolt right in. The only problem is going to be gear ratio as the 1972 to 1975 Dana 20s tend to be 3.73.

What Gert says about the Lockright is true; in a CJ5 squirrely is just a way of life and on ice or a wet road the rear end can try to pass the front if you run one. I don’t recommend it on any street rig.

 

[thiswontbetooexpensive]

After looking through the responses here and exploring options, I have made the decision to just leave it be. Upon further inspection, I think the most economical decision right now is just replace both brake drums and all the brake componets, I'm going to replace al the brake lines anyway with SS, and give it a whirl.

I dont plan on testing this up a mountain anytime soon or doing any rock climbing or anything. The PO had never had any issues with the rear differential and all the bearings and seals are in great shape. (I think it would be a push to say he put more than 2,000 miles per year on the Jeep for the last 20 years he has owned it!) Even minimal wear on gears. When I took the axle nut cover off, there wasnt even any rust on the nut or threads. It all looks like the rest of the vehicle, pretty good for age.

I will just try and see if it breaks with the driving I will do on it. If that occurs, I will go with the one piece axles at that point.

Again, thanks for the input!

 

[mtnwhlr]

I've wheeled mine pretty hard and still have a stock AMC20 . But I run 31-10.5s and no locker.

 

[thiswontbetooexpensive]

That was my thoughts as well. I'm going back with the same tires that were on it. I believe they were 31x10.5. Maybe 30's. Time will tell if it holds.......


This won't be too expensive Dear! That's what I keep saying. Over and over again.