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Jeep Axle: AMC 20

AMC 20 rear axle

Front Axles

Dana 44
Dana 30
Dana 27
Dana 25

Rear Axles

Chrysler 8.25"
Dana 35c
AMC 20
Dana 30
Dana 60
Dana 53
Dana 44
Timken
Dana 41
Dana 23

Jeep Axles

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General


All AMC 20s have a 8 7/8" R&P and use a 29 spline shafts. The AMC 20 R&P is 3/8" bigger than the Dana 44, but it uses smaller shafts, smaller axle tubes, and the CJ version comes with weaker two piece shafts. The AMC20 uses a 29 spline shaft where as the later Dana 44 uses a 30 spline shaft. The AMC 20 housing tends to flex a lot which can cause breakage. This can be remedied by welding the tubes and/or adding gussets. The reason the AMC 20 flexes more than the Dana 44 is the shorter differential housing and smaller axle tubes. It's other flaw is the CJ version uses the two piece axle made up of a hub and a shaft. The hub end tends to break off under load which has created the market for one piece AMC 20 axle shafts. Unfortunately, the shafts are expensive ($350+ USD) and in some cases a special bearing must be used.

Identifying the gear ratio of an AMC 20 is a bit tricky. Dana axles normally have a tag on the left of the diff cover with the gear ratio at the time of build. The AMC axles have a code that has to be looked up in a table. The code is stamped on the housing boss to the left of the diff cover right near the axle tube. Good part about the stamp is it tends to stay readable longer than the tag, but you have to know the code. Since there are conflicts between what a code means for a narrow track and what it means for a wide track, don't count solely on the code to identify an axle. Bring a tape measure or know the source of the part.

Specs

Narrow Track AMC 20
Code Gear Ratio Diff Type
AA 2.73 Open
DD 2.73 Trac-Lok
BB 3.31 Open
CC 3.31 Trac-Lok
A 3.54 Open
N 3.54 Trac-Lok
GG 3.73 Open
Q 3.73 Trac-Lok
L 4.10 Open
M 4.10 Trac-Lok
Wide Track AMC 20
Code Gear Ratio Diff Type
D 2.73 Open
DD 2.73 Trac-Lok
B 3.31 Open
BB 3.31 Trac-Lok
A 3.54 Open
AA 3.54 Trac-Lok
H 3.73 Open
HH 3.73 Trac-Lok
C 4.10 Open
CC 4.10 Trac-Lok
The Trac-Lok is a limited slip differential. You may have to scrape away a lot of mud, paint, and rust to uncover the code. If you can't find the code on the rear, check the tag on the front axle. Both axles should be geared the same.

The R&P ratio ranges supported by the carriers are 2.73 and 3.31-5.13. The 5.13 gear ratio is not available for the Dana 30 though, so it is rare to see it. 4.56s are the lowest common ratio between the Dana 30 and AMC 20. 5.13s are available for the Dana 44.

CJ AMC 20

The CJs used two versions of the AMC 20, the narrow track from '76-'81 and the wide track from '82-'86. Both versions use keyed, two piece shaft/hub design and 5 on 5.5" wheel bolt pattern. Supplies of AMC 20s were exhausted in 1986 and some Dana 44s were used instead in the last of the CJ-7s.

From 1976-1978 a larger 11x2" drum brakes was used on the AMC 20. After 1978, a 10x1.75" drum was used.

SJ AMC 20

The Wagoneer and full size Cherokee also used a narrow and wide track version of the AMC 20. Both SJ versions used once piece shafts and 6 on 5.5" wheel bolt pattern. Since the length and bolt pattern is different from the CJ version, the SJ shafts are not compatible without resplining and redrilling. I've never heard of anyone going to the trouble.

Model/Version Spring Pads Wheel to Wheel Years
AMC 20/CJ Narrow Track 36" 50.5" '76-'81
AMC 20/CJ Wide Track 36" 54.5" '82-'86
AMC 20/SJ Narrow Track
AMC 20/SJ Wide Track

Last modified Wednesday, 01-Dec-2010 09:14:51 MST


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josue (8/17/2012)
is compatible a Wagonner axle 76 with a Cj7 84??

JC (5/23/2012)
I have a 1985 CJ7m Jeep that is making an awful noise from the rear end when straining or spinning. I am trying to determine if it is the axle or the rear end that needs to be replaced. I cannot find gear/ration numbers. Thanks.

Martyl@live.com.au (3/3/2012)
Treagin pack your bearings by hand whith heavy duty grease as they are not fed by the diff oil Have had same problem myself I use Moreys grease super red Martin


treagin@bellsouth.net (2/6/2012)
'79 CJ5, with one piece axles. Repalcment axles were in the jeep when I bought it. About every 500 miles or so an axle will walk out of the housing. Passenger side twice, now the driver side has walked out. I have replaced bearings and seals myself once, and had a mechanic do so twice. HELP!

Deepcbill@yahoo.com (1/31/2012)
The measurement width is taken from where to where?
I ask this cause i measured from axle where brake drum is connected and i was on the asumption i have a wide track measuring 51 1/4 inches.


greg (12/25/2011)
kenny did you fig. it out if not your frickshions are warn out in the amc 20 track lock can be changed out by pulling the axels and diff cover im going though it my self.

james (10/11/2011)
Was wondering where one could find an AMC 20 backing plate. 11 inch, for the driver side, or both. I keep loosing bearings. If you know of anyone who might have an idea where I can get one

randy (7/20/2011)
I just acquired a '70's ford t18. I have an 80cj5 iron duke. I have read that the bell housing is gm on engine side and ford on tran. side. Will the t18 bolt up? what other problems can I expect? I am considering some sort of locker on the rear. Is it a bad idea to use the amc 20? can you weld the hubs to the axles or use jbweld (just kiddiing). I don't do any hard core crawling. thanks for the help.

KENNY (4/16/2011)
I Have a 1977 Cj with AMC 20 and3.54 factory Track-Lock and Rear and front hook up both tires but when I need them too hook up all power goes to one tire is this just the way this system works
Kenny Cuda29@aol.com

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