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Amc 20

J

jeepboy_90

NAXJA Forum User
Location
Santa Cruz
Is a AMC 20 out of a 1987 MJ any good. Looks beefy. Did a search and only came with a little info.
 
As far as the 20 goes, I left my 20 in my 79 CJ and am very happy with it, I have changed the shafts to one piece, which is the major down fall of the 20, and I put an Auburn LS in as well which is stronger than the factory carrier. Another down fall of the 20 is the weak axle tubes, which can be trussed.

The strong point to the 20 is that the ring and pinion are larger than a Dana 44 which is a real good reason to keep a 20.

they're not junk, just need some help.

dan
 
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Most 86 MJs with the heavy duty Metric Tonne package will have the AMC-20. The AMC-20 has gotten a bad rap because of the lousy 2-piece shafts in CJs and the thin tubes can have problems under the weight of an SJ. MJs have neither the 2-piece shafts, nor the weight of the SJ.
Overall, they are much better than a Dana 35, but not quite as desireable as the Dana 44. Oh and 4.10 gears were common.
Jeep on!
--Pete

My 86 MJ:
63359849.jpg
 
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The Model 20 was the optional heavy-duty MJ rear axle for 1986 only. AFAIK it was not used in the XJ. The ring gear is about the same size as a Dana 44, the MJ version had one-piece axle shafts, and lockers are readily available. It's actually a very good axle, the biggest drawback being that HUGE pumpkin reduces ground clearance a bit, and I don't think you could shave it. If you have one, I wouldn't worry about looking for a replacement. And if you can find one cheap I wouldn't turn up my nose at it.
 
In the picture that PeteM posted, is there some reason that the shocks are in FRONT of the rear axle? Both my '87 and my '88 MJ have the shocks for the rear axle behind the housing and tilted to the rear. Is this the factory mount for the Metric Tonne package?
 
Just wanted to know because there is an axle like this at the pick-n-pull in south San Jose.

Good Luck.
 
One other thing to be aware of with the AMC 20 - it'll only go as low as 4.56:1 ratio gearing.
 
ren said:
In the picture that PeteM posted, is there some reason that the shocks are in FRONT of the rear axle? Both my '87 and my '88 MJ have the shocks for the rear axle behind the housing and tilted to the rear. Is this the factory mount for the Metric Tonne package?
Click to expand...
Are yours long beds or short beds?
 
Root Moose said:
One other thing to be aware of with the AMC 20 - it'll only go as low as 4.56:1 ratio gearing.
Click to expand...
Strange, I put 4.88s in mine.....
The FSJ/MJ 20 is a very good upgrade for the D35 if you get it cheap. Only thing, if you use one from the FSJ, you'll have a different bolt pattern from your front axle, but there are ways to fix that.
 
ren said:
Both of my MJs' are short beds.
Click to expand...
The 86s were all long beds, and the metric tonne package was only available on long beds. I think that's the difference. Long bed vs. short bed.
 
Root Moose said:
One other thing to be aware of with the AMC 20 - it'll only go as low as 4.56:1 ratio gearing.
Click to expand...


mine has 4.88's in it so i guess you can go lower
 
jmaxj said:
mine has 4.88's in it so i guess you can go lower
Click to expand...
Are you certain they are 4.88s? The data I've been able to collect on the AMC Model 20 shows 5.13 as being an available ratio, and 4.56, but nothing in between. 4.88 would be a logical "in between" ratio, but so far I've never seen any reference to it.
 
Been running an MJ M20 for......4yrs IIRC. Sporting 285's, I run 4:56's and an Auburn Pro L/S plus Ford SVO disc kit. Only complaint I have with mine is that the driver's side seal leaks, again.
 
Eagle said:
Are you certain they are 4.88s? The data I've been able to collect on the AMC Model 20 shows 5.13 as being an available ratio, and 4.56, but nothing in between. 4.88 would be a logical "in between" ratio, but so far I've never seen any reference to it.
Click to expand...
I put 4.88s in mine. They exist.
 
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