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Discussion Starter #1
So, here we go... I am restoring a 1962 J-300 Pickup... In the rear is a Dana 53 (Old but sturdy piece of gear) I'm looking at an '85 FSJ as a donor (360, 3 speed auto) However for simplicity's sake I'd like to simply swap the cabs...
Both are the 120" wheelbase... I need to know how much abuse can that Corp 20 take?
Is running an AMC 20 on 37's like Running 31's on a turdy 5??

I should note these are the ones with a single piece axle... If it can handle it I'll weld the housing to the tubes and fab up a small truss... If It won't then I'll just use the J-300 diffs with the 4.27 ratio (Beats the socks off the retarded 3.31 ratio on the donor truck)

Cheers folks
 

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I can only go by what I've heard. I've had one AMC 20 in my CJ (of course it wasn't the Corp. version). I did beat the piss out of that one on 33s with an AMC 360 then with a SBC 383 stroker. It never broke. I actually broke 2 driveshafts before I pulled that axle.

The Corporate 20 is slightly wider than the "regular" 20s, and already has 1-piece axles, as you already know. The only other weakness that I know of with them is the tubes possibly twisting in the diff housing. So, as you already said, you could weld the tubes and build a truss. I've heard that these are stronger than 44s. They do have the same ring gear size as a GM 12 bolt at 8 7/8". I believe they only have 29 spline axles, but I'm unsure of their diameter, as well as the diameter of the pinion.

If you're not too hard on it, I'd say roll with it til you either break it or find a different axle you want. Hell, I've got 38.5 Boggers on my 12 bolt and 44 combo. Of course, I don't play in the rocks, either.
 

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i personaly feel that the amc20 was the grand prise winner in the "shittiest axle possible" design contest.

2 peice axles that break loose and spin because they have no intermeshing splines.
center slugs that collaps under side load.
full tear down of breaks to change a wheel bearing.
grease packed wheel bearings.
micro torx tip cover bolts.
ultra thin diff cover, i think a kitchen mixing bowl is heavier duty.
a full width bare housings weighs 51lbs, thanks to the .125 tube walls


sure they are great axles if you throw an extra $300 for shafts at them, which still leaves you with a giant pile of shit with $300 axle shafts stuck in it.
Then there's that... I forgot about the thin diff cover. Like I said, the only people in my circles that I know of that successfully run the AMC 20 are ones in mud/sand racing.
 

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Discussion Starter #5
Thanks scooter, good to know :D

i personaly feel that the amc20 was the grand prise winner in the "shittiest axle possible" design contest.

2 peice axles that break loose and spin because they have no intermeshing splines.
center slugs that collaps under side load.
full tear down of breaks to change a wheel bearing.
grease packed wheel bearings.
micro torx tip cover bolts.
ultra thin diff cover, i think a kitchen mixing bowl is heavier duty.
a full width bare housings weighs 51lbs, thanks to the .125 tube walls


sure they are great axles if you throw an extra $300 for shafts at them, which still leaves you with a giant pile of shit with $300 axle shafts stuck in it.
Hahaha thanks for the response, I'm aware the cj style were pretty Shitty on a good day, I know that this one has single piece, thicker shafts and 0.25 in thick axle tubes... Not sure on the shaft diameter, I think I read 1.6 in, not too bad if its true, that's the same as a Ford 8.8 (almost 1.61) and plenty of guys run 37's on them...

So we are on a similar page, dont expect a God axle, light on the skinny peddle then wheel it till it busts, then go Dana 53
 

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Discussion Starter #6
Then there's that... I forgot about the thin diff cover. Like I said, the only people in my circles that I know of that successfully run the AMC 20 are ones in mud/sand racing.
Ok, the diff cover is made out of tin foil...
Another plus is its a semifloat.
 

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Discussion Starter #7 (Edited)
yeah, they are 1.6 at teh bearing neck, but that not where it counts and thats not where they break.

i measure one in a few min and post back.

Thanks mate! :D

Where do they normally bust? I'm guessing at the spline at the diff end... or they'll snap right where the bearing sits..

Bearing in mind ;) I'll probably run it open too.. Strangely I'm getting the idea this axle isn't entirely worth my time....

However some quick reading I did just told me the Axle diameter of a Dana 60 is only 1.41" and 1.5" .... How the hell does that work :confused:
They both have the same pinion shaft diameter of ~1.6"

Corp 20 - 29 splines w/ 1.6" axles...
Dana 60 -31 splines w/ 1.5" Axles... 1.5 has got to be wrong... That spells the Corp 20 as the tougher axle :eek: If that were true we'd all be running the bastards...
 

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Discussion Starter #9
again. you are not comparing the right things.

the amc20 is 1.6 at the bearing seat. more like 1.1 at the spl.

35spl d60/70 is 1.5 at the spl. 1.4 at the root/1.5 at the major.


sorry i got caught up at work an didnt get the measurement.
Thanks mate :D

No no, I wasn't doing it deliberately... I was under the impression that it was 1.6" across the axle shaft AS WELL as the pinion shaft... like I said, I was mistaken, and Don't be sorry mate, you are doing me a favour :D
 

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AMC model 20 1.25" diameter shafts at splines 29 spline count and came with 2 piece shafts and thin tubes

The FSJ amc m23 is the same spline count and same diameter, but did come with one piece factory shafts and thicker tubes.


alot of rear ends share the set 20 and set 10 bearings and the associated ID.


plenty of guys have run the M23 in cjs up to 35's and 36's. Im a little more of a dana spicer fan but the m23 will do the job your talking about for awhile
 

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Discussion Starter #11
AMC model 20 1.25" diameter shafts at splines 29 spline count and came with 2 piece shafts and thin tubes

The FSJ amc m23 is the same spline count and same diameter, but did come with one piece factory shafts and thicker tubes.


alot of rear ends share the set 20 and set 10 bearings and the associated ID.


plenty of guys have run the M23 in cjs up to 35's and 36's. Im a little more of a dana spicer fan but the m23 will do the job your talking about for awhile
Thank you very much! That's the sort of tech I was chasing :dustin:
so on 37's it'll be happy in the mud and in the sand, but if I've had two goes at a frame twister climb in crawl, let the ego get the better of me, give it some boot... don't be suprised when it breaks?

Sounds like a reasonable piece of gear... but I won't be throwing money at it...

I know a bloke down the road with a CJ7, It runs 35" Boggers, and a 360 on NO2 and he has it on M23's.. no breaks in about 5 years...
 

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Running a 1981 m23 in my yj with 35's. I have welded tubes and a truss. The previous owner had upgraded to after market shafts. Running 4:88 gears. The only issue that I had with the axle was the POS auburn ected locker whose spider gears broke while climbing a ledge. For northeast style wheeling that I do its worked for me since 2008.
 

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AMC20, in a 3500lb CJ7, 10+ years of wheeling on it locked with 35" tires. Had one axle shaft bearing failure , otherwise trouble free.

Specs: sleeved, trussed housing, aftermarket dif cover, Superior 1 piece axle shafts.

Wally
 
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