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AMC 20 rear axle swap

J

joeyschribar

NAXJA Forum User
Location
Edmonton
86 grand waggy, is it worth my time to swap in the rear axle, an AMC 20

if i do, will the stock shock mounts work and will the stock spring perches fit as well?
thanks all!
 
I am not sure if the grand waggys had the two piece axles of the AMC 20 or not but, personally I would not switch in the AMC axle. The 20's under CJs had two piece axles if I remember correctly
 
you wanna put an AMC 20 from a waggy under an XJ???

With the 1piece shafts and welded tubes, the 20s are good axles. waggy axles have 5 on 5.5 though.
 
A model 20 is a bit better than a D35, but it still has issues. The tubes are a bit weak, and tend to bend or spin. Plug welding the centersection and trussing it would be good. If it has 2-piece axles, get aftermarket 1-piece ones. The covers are notoriously thin as well, build a guard for it or buy anaftermarket one.

Personally, I'd put a better axle under it than the model 20.
 
fubar XJ said:
A model 20 is a bit better than a D35, but it still has issues. The tubes are a bit weak, and tend to bend or spin. Plug welding the centersection and trussing it would be good. If it has 2-piece axles, get aftermarket 1-piece ones. The covers are notoriously thin as well, build a guard for it or buy anaftermarket one.
.
Click to expand...

Inaccurate info above on the FSJ axle :(

The AMC 20 under a FSJ or Comanche is not like the CJ units AT ALL. I run a factory Comanche AMC 20 in my Comanche
They have thick tubes and one piece shafts. They are very strong version of the AMC20, Way stronger than a turdyfive. they are about as strong as a D44. Larger ring gear and pinion than the 44 but 29 spline shafts to 30”.but I have not seen the spline count be an issue, the shafts most often snap before splines strip.well I have never seen them strip?
But they have very little after market support. also As noted if a FSJ axel its 5x5.5.
Trussing any axle is a good thing :) and is recommended.
If your getting a good deal then go for it the axle is strong. but if you can get a D44 for the same price its a better deal simply due to after market axle shaft support.
 
Comanchedude said:
Inaccurate info above on the FSJ axle :(

The AMC 20 under a FSJ or Comanche is not like the CJ units AT ALL. I run a factory Comanche AMC 20 in my Comanche
They have thick tubes and one piece shafts. They are very strong version of the AMC20, Way stronger than a turdyfive. they are about as strong as a D44. Larger ring gear and pinion than the 44 but 29 spline shafts to 30”.but I have not seen the spline count be an issue, the shafts most often snap before splines strip.well I have never seen them strip?
But they have very little after market support. also As noted if a FSJ axel its 5x5.5.
Trussing any axle is a good thing :) and is recommended.
If your getting a good deal then go for it the axle is strong. but if you can get a D44 for the same price its a better deal simply due to after market axle shaft support.
Click to expand...

My Waggy has stock axles, with the rear AMC 20, and it is 6 lug.
 
mine is 6 lug as well, no problem as i have rims that fit it.


all i want to do to the amc 20 is 4.10 gears and a minispool or lockrite of some sort.

just wondering if its a wider axle, and can i just bolt it up to the existing spring perches.
I would measure it but i have to drive about an hour away and its bugging me!
Seems like there wont be all that much to fab on it for the rear, just spring perches and maybe shock mounts if i have to.
Am i able to get 4.10 gears for the amc 20?
thanks!
 
joeyschribar said:
mine is 6 lug as well, no problem as i have rims that fit it.


all i want to do to the amc 20 is 4.10 gears and a minispool or lockrite of some sort.

just wondering if its a wider axle, and can i just bolt it up to the existing spring perches.
I would measure it but i have to drive about an hour away and its bugging me!
Seems like there wont be all that much to fab on it for the rear, just spring perches and maybe shock mounts if i have to.
Am i able to get 4.10 gears for the amc 20?
thanks!
Click to expand...

I would say its wider, by and inch or two? don't know for sure but expect it to be a bit wider. you should plan to reset the perches as im fairly sure the FSJ is SUA and XJ is SOA
you can get gears up to 4.88 for the AMC20
 
Jess said:
make sure the rear diff is centered and not offset...I know some of the Waggys were.
Click to expand...

thats the most important thing to look at right there. the Quadratrac t/case offsets both differentials to the passenger side. FSJ M20s "should" already have 1-peice shafts, with 6x5.5 pattern. i have a waggy front at the shop that measures 61" wide. wide enough to allow you to use the waggy stock wheels.
this is how i trussed the M20 in my CJ-5, also welded the tubes. the nut/bolt on the passenger side is to relocate the brake line since the truss covered the original location. and the rear cover is paper thin.. i have a custom cover coming from Banditt Offroad soon.
overall its a good axle comparable to a D44.. just a real PIA with the mis-matched bolt pattern.


standard.jpg
 
Is it just me or do those axle tubes bend up? not to get off topic or anything just curious.
 
I wheeled an FSJ for a long time with a M20 welded with 35 inch tires. I never broke anything. It held up very well. It does come with one piece axles. Just not as much aftermarket support as say a 44 or 9 inch.
 
thanks for the info guys

i hope that rear diff is not offset
also, since is it a wider axle, is it okay to run it at a wide axle in the rear while keeping the stock width 30 up front, i will cut the spring perches off and make my own, and center them.
does anyone know what kind of angle the diff should be pointed at, i would probably make it slightly pointing up towards the t-case for better driveline angles, or is this something that needs to be precise?

thanks once again for info, i am going to be doing this swap if i can get cheap 4:10 gears for it.

anyone know of any places that sell gears?


 
Why not just grab a 29 spline 8.25? Think how easy an 8.25 would just bolt right in. The 20 is probably a little stronger than the 8.25, but several people have run the 8.25 with 35s and havent had any problems. I guess the big drawback of the 8.25 is you cant run 4.88s.
I know you are probably getting a deal (or free) AMC20, but by the time you address the spring and shock mounts and the bolt pattern you would have a decent amount of labor involved in the 20.
 
Comanchedude said:
Inaccurate info above on the FSJ axle :(

The AMC 20 under a FSJ or Comanche is not like the CJ units AT ALL. I run a factory Comanche AMC 20 in my Comanche
They have thick tubes and one piece shafts. They are very strong version of the AMC20, Way stronger than a turdyfive. they are about as strong as a D44. Larger ring gear and pinion than the 44 but 29 spline shafts to 30”.but I have not seen the spline count be an issue, the shafts most often snap before splines strip.well I have never seen them strip?
But they have very little after market support. also As noted if a FSJ axel its 5x5.5.
Trussing any axle is a good thing :) and is recommended.
If your getting a good deal then go for it the axle is strong. but if you can get a D44 for the same price its a better deal simply due to after market axle shaft support.
Click to expand...

You got me. I was thinking of a CJ 20, not absorbing his statement it was a Waggy one.

My bad
 
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