Sacredgroove
New member
must be due to all the mud caked underneath,but i cant find the code on my amc 20 to find out what gear ratio i have and tag from dana 30 is missing...where is it at on the housing? thanks!
am i blind? differential code on amc 20..where?
- Thread starter Sacredgroove
- Start date
What a coincidence! I just looked at mine a couple of days ago. It is to the right side of the diff facing out. It is on the axle boss right before you get to the shaft. I had to use degreaser and a scraper to expose it. I hope you don't find a single "D" like I did! 
Good luck!
Good luck!Sacredgroove
New member
thanks! i found it much the same fashion...degreaser and a cloth. i have the "BB" 3:31 with trac lock- not sure if the limited slip is a plus in the axle or not-guess it is? doesnt matter...locker going in soon heheh
i appreciate your help!
i appreciate your help!
That's what it came from the factory with. The only way to know exactly is to pop the cover and if it isn't stamped in the edge of the ring gear, then you need to divide the number of teeth on the ring gear by the number of teeth on the pinion. Sometimes the tooth count will be stamped on the ring gear, like 41-10, 41 is the number of ring gear teeth and 10 is the number of pinion teeth, if you divide 41 by 10 you get a 4.10:1 ratio.
You can get close by putting the rear axle on jackstands and putting the transmission in neutral, then marking the tire and marking the driveshaft, then turn the rear axle one complete revolution and count the number of times the driveshaft spins. If the driveshaft spins 3 1/2 times then you have a 3.50:1 ratio. They only make certain ratios for certain axles so this will get you close enough to figure out what you have.
You can get close by putting the rear axle on jackstands and putting the transmission in neutral, then marking the tire and marking the driveshaft, then turn the rear axle one complete revolution and count the number of times the driveshaft spins. If the driveshaft spins 3 1/2 times then you have a 3.50:1 ratio. They only make certain ratios for certain axles so this will get you close enough to figure out what you have.
Sacredgroove
New member
do the gear ratios of the front and rear differentials have to match..3:31 and 3:31? i assume they do but am not sure on that. thanks for the replies everyone!
Bucky said:Yes, the ratios have to be the same. I was really hoping to find a single H (3.73) but instead have 2.73's. My crawl ratio is a whopping 27:1! Woo- oh... wait, no.
I thoroughly checked mine out a week before I had my 1 piece axle shaft put in my 20.I thought the code was DD(4.11) but it wasnt.It was 2.73!Now I have my 4.11's!
You know, after reading a bunch of stuff on the internet, I just assumed I had 3.73's. Of course, what happens when one assumes? Exactly. So, when I finally looked at the service manual, I saw these codes. And sonofa... Well, not trying to change the reason for the post, but if I were to run a maximum tire size of 32" to 33", would 4.11's be overkill? I'm not going to rockcrawl, I just want to get through a little mud, snow, and the occasional hill to get to the fishing. Would 3.73's be enough? Also, I would like to be able to go 75mph on the highway.
I am running 4.11 gears with 33's on my CJ7(258).I had the 4.11's when I had 31's and it was running high rpm's doing highway speeds
(2500-2700rpm's).Would easily do 80mph in 5th gear.Now with the 33's and the 4.11's it comes out just about right.Back to regular rpm's at high speeds and it isnt sluggish on the street.
(2500-2700rpm's).Would easily do 80mph in 5th gear.Now with the 33's and the 4.11's it comes out just about right.Back to regular rpm's at high speeds and it isnt sluggish on the street.
Bucky said:What a coincidence! I just looked at mine a couple of days ago. It is to the right side of the diff facing out. It is on the axle boss right before you get to the shaft. I had to use degreaser and a scraper to expose it. I hope you don't find a single "D" like I did!
So I'm guessing my D is a 2.73 open diff right?
What are the other codes for these things. I've got my trail rig at my parents I need to check too. Thanksnever mind, did a search......
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
Of course I have the dreaded "D" :x Hopefully my trail rig has something a little better.......(gotta check next time I'm at the parents)
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
Of course I have the dreaded "D" :x Hopefully my trail rig has something a little better.......(gotta check next time I'm at the parents)
Sacredgroove
New member
got this from off-road.com a good reference for all the dana series and amc 20 at the website:
http://www.off-road.com/jeep/tech/axle/amc20.html
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
http://www.off-road.com/jeep/tech/axle/amc20.html
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
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