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AMC 20, 4.0 swappage questions for the 86 MJ


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i can't see to search this for some reason so i will ask some of you to tell me about it...

 

so far i get the idea that it is a great axle. and i found a sticker inside the truck that leads me to believe that it has a factory rear locking differential.

 

also, i have been told not to bother swapping in a 4.0. why is this?

 

help this MJ neophyte out please. :wavey:

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No clue. The AMC 20 has a bad name because of the 2 piece shafts they had in CJs. The Comanche AMC 20 has single piece shafts, and is quite strong. But as it's not very popular, there's not a lot of after market support for it. If it has a locker, great. If it doesn't, I doubt you will find one for it.

 

Simplest way to tell for sure is to pop the cover and see if there are 4 little gears in the middle (2 spider gears, 2 axle gears). 4 gears plainly visible is open, anything else (closed case, complicated mess of parts etc.) means limited slip or locker. Should probably pop the cover to drain the old oil anyway. After 23 years and who knows how many miles, it could use some fresh lube.

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The MJ M20's either came 'open', or with a Trac-lock LSD. (all with 4.10's)

 

Trac-lock's are clutch type LSD's, with a belleville spring, a one piece carrier, and 2 pinion gears (+ the two spiders on the axle shafts).

 

Early M20's (pre 1971) had used stronger 'powerlocks' (2 piece carrier, 4 pinion gears).

 

AMC 20's have a bigger ring gear than a D44 (8.875" vs 8.5"), but with less ring gear bolts (8 vs 10), and slightly smaller axle shafts 29sp vs 30 sp (FWIW 29sp AMC 20 shafts are bigger than Mopar 8.25's 29sp shafts).

 

mvusse is right on about it's strength, and undeserved bad rep (AMC 'cars' also got 2 piece shafts, MJ's & FSJ's got flanged 1 piece),

 

but there are lots of lockers available.

Even though they look totally different (& are IFS/IRS), H1 Hummers still use an AMC-20 center housing,

maybe that's one reason locker companies keep making AMC-20 versions of their new stuff:

 

https://www.4wdfactory.com/store/produc ... ric-Locker

 

http://www.ox-usa.com/ox/VehicleApplica ... fault.aspx

 

http://store.arbusa.com/ARB-Air-Locker- ... P3543.aspx

 

https://www.4wdfactory.com/store/produc ... oit-Locker

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..Who told you not to swap in 4.0? Sure, it's a lot of work, but well worth the upgrade if it's what you want.

 

I did, kinda. I just told him that a 3.4 swap would be a direct bolt in, and that the 4.0L could be done, but would need more modification than a '87-'92 4.0L swap. :dunno: Namely firewall massaging and odds/ends. But if you are up for it, its not too bad. ;)

 

Rob L.

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so, how about the amc 20 locker deal? anyone else??

The factory never sold the AMC 20 (or any other axle) with a locker. They did sell a lot of limited slips, and there's a good chance that's what is in your AMC 20.

 

Eagle,

I thought I had you on a technicality, but I was wrong. :doh:

 

AMX/SS's M20's came with 4.44 gears, and aftermarket 1 piece shafts,

unclesam4.jpg

 

I had thought they also were delivered with Detroit's (No-Spin), but it looks like they just got Power-Lok's (Twin Grip).

 

 

Your statement remains intact :cheers:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It was available in the 70's as a dealer option tho. ;)

 

 

AMC Group-19 parts list:

 

 

448 6719 Cam and kit (302 advertized duration hydraulic lifter)

448 8475 Blocked heat riser manifold gasket

448 5728 Edelbrock R-4B intake manifold

448 5730 Holley 950 three barrel carburetor

448 7900 Mallory YL flat cap distributor w/o tach drive

448 7901 Mallory YL flat cap distributor w/ tach drive

448 8059 Mallory Voltmaster coil

448 6228 Edelbrock Crossram STR-11 intake manifold* (std. on SS AMXes w/ 2-660 Holley #4224)

448 5742 Delco capacitor discharge distributor and ignition box

448 7989 Crane Gold roller rockers with studs

4486997 Detroit locker differential

448 5741 Aviad oil pan

448 5726 & 448 5727 Doug's headers w/ removeable tube for starter removal

Rear gear sets;

448 5749 3.73

448 5750 3.91

320 8546 4.10

320 9854 4.44

448 6587 5.00

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..Who told you not to swap in 4.0? Sure, it's a lot of work, but well worth the upgrade if it's what you want.

 

I did, kinda. I just told him that a 3.4 swap would be a direct bolt in, and that the 4.0L could be done, but would need more modification than a '87-'92 4.0L swap. :dunno: Namely firewall massaging and odds/ends. But if you are up for it, its not too bad. ;)

 

Rob L.

naw, it wasnt rob... there was a fella on another board that poo-poo'd on my 4.0 ambitions. (i like the 3.4 too btw)

 

thanks for the info and i will crack that rear end open soon enough and will shed light on whatever gears and if its got a limited slip or no..

 

thanks guys! this is proving to be very interesting for me from the get go! :cheers:

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The MJ M20's either came 'open', or with a Trac-lock LSD. (all with 4.10's)

 

Trac-lock's are clutch type LSD's, with a belleville spring, a one piece carrier, and 2 pinion gears (+ the two spiders on the axle shafts).

 

Early M20's (pre 1971) had used stronger 'powerlocks' (2 piece carrier, 4 pinion gears).

 

AMC 20's have a bigger ring gear than a D44 (8.875" vs 8.5"), but with less ring gear bolts (8 vs 10), and slightly smaller axle shafts 29sp vs 30 sp (FWIW 29sp AMC 20 shafts are bigger than Mopar 8.25's 29sp shafts).

 

mvusse is right on about it's strength, and undeserved bad rep (AMC 'cars' also got 2 piece shafts, MJ's & FSJ's got flanged 1 piece),

 

but there are lots of lockers available.

Even though they look totally different (& are IFS/IRS), H1 Hummers still use an AMC-20 center housing,

maybe that's one reason locker companies keep making AMC-20 versions of their new stuff:

 

https://www.4wdfactory.com/store/produc ... ric-Locker

 

http://www.ox-usa.com/ox/VehicleApplica ... fault.aspx

 

http://store.arbusa.com/ARB-Air-Locker- ... P3543.aspx

 

https://www.4wdfactory.com/store/produc ... oit-Locker

 

:hijack:

 

Off topic, but I just wanted to mention that you have some very detailed and informative posts with some obscure facts. I really enjoy reading your posts and learning from them. :thumbsup:

 

Willy

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Eagle,

I thought I had you on a technicality, but I was wrong. :doh:

 

AMX/SS's M20's came with 4.44 gears, and aftermarket 1 piece shafts,

unclesam4.jpg

 

I had thought they also were delivered with Detroit's (No-Spin), but it looks like they just got Power-Lok's (Twin Grip).

 

 

Your statement remains intact :cheers:

I'm greatly relieved to know that my reputation is (temporarily) intact, but I wasn't intending to take in the totality of AMC vehicles in my response. The question was about an '86 MJ and that's what I meant by "the factory" -- the Jeep factory, in MJs.

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I'm greatly relieved to know that my reputation is (temporarily) intact, but I wasn't intending to take in the totality of AMC vehicles in my response. The question was about an '86 MJ and that's what I meant by "the factory" -- the Jeep factory, in MJs.

 

lol.

 

Glad this was taken in the spirit it was written. :yes:

 

:cheers:

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