AMC20 Gear Ratio?

Recently picked up a '86 LWB 2WD V6 MJ with an AMC20 in the rear. I've hunted for what "should" be in it, and hunted for a tag on the diff itself to no avail. I bought the MJ for the rear axle as I know what a rare bread the MJ AMC20 is and have been hunting for one for awhile; but I have no clue what gear ratio it'll have in it.

Before tearing the cover off I thought I'd see if anyone knows what it "should" have. It'll eventually get regeared anyways, but I thought if it matched one of the D30's I have laying around the swap into my other MJ would be a bit easier.

Anyone have any clue? Thanks in advance! :cheers:

Is the stamped code readable?

http://www.jeeptech.com/axle/amc20.html

I knew I was missing something. After a bit of hunting (scraping off the old dirt) I was able to find it.

Also just for future reference it's located to the pass side (right) of the axle; not the left as the link above says. Once I knew were to look I didn't have any issues finding it.

Also for reference mine was marked out as "C"; which according to the above link is 4:10/open. Exactly what I was hoping for as it'll match my built D30 already in my MJ! :clapping:

Here is a pic I found online (not mine) of where it's located.

So you have the wide track version?

i would just pull the cover and check it that way....buddy and i were at the junkyard the other day and he found a d44 for his XJ and it was stamped 4.10's....he got all excited and instead of checking like i told him to he payed a hefty amount...got it home and it was 3.07's so now he has to spend the money to re-gear now :fool:

:agree:

So you have the wide track version?

Heck I don't know... :oops:

I just assumed that they were considering it the wide track since I don't think the narrow track was made in 1986. But that's just going off of what I've found online.

I also assumed it was the wide track since they are calling FSJ Waggy's a wide track and the Waggy axle's are narrower than the MJ axle's are.

And lastly the "C" I found on my axle according to the info I found was only stamped on wide track's.

So for what that's worth I'm assuming it's the wide track; however I can't find any info on the MJ AMC20 anywhere to confirm that's what AMC called them...

Yeah I plan on pulling the cover and verifying before I do anything major with it. I just was interested in seeing if I could try to figure it out prior to doing so. If anyone else has any info on the MJ AMC20 they'd like to contribute I'm all ears. :chillin:

what was the engine/trans on the MJ.....v6/? Auto or 5spd

what was the engine/trans on the MJ.....v6/? Auto or 5spd

It's the V6, as for the tranny it's either the AX4 or the T4 or T5. I honestly haven't looked at it closely cause it's all coming out for something different. Next time I'm under it I'll take a look at the tranny.

if its a 5spd...from all the 86's i have seen with a v6 and 5spd have 99% of the time been a 4.10 ratio

Ok according to the VIN (yeah it's cold and rainy outside) this is what it's got.

1JTWW6613GTxxxxxx

5spd (no transfer case)

4x2 7ft bed

I can't seem to find a code for the 4th digit (engine code) as W though. However I'm 100% sure it's the V6....

There is no wide or narrow track widths on XJ/MJ's!! :shake: Thats a CJ/FSJ thing.. get your acronyms right soldier!! :rotf: :rotf: :doh: :yes: :brows:

They are all 60" WMS-WMS!!

CW

Okay, then the axle ratio codes are wrong on the link I posted above. Code "C" (4.10 open) is for a wide track axel. Motion, could you measure the axel length when you get a chance?

So you have the wide track version?

What wide track version? Was there a wide track version in the MJ?

Nobody ever tells me nuthin'!

There is no wide or narrow track widths on XJ/MJ's!! :shake: Thats a CJ/FSJ thing.. get your acronyms right soldier!! :rotf: :rotf: :doh: :yes: :brows:

 

 

They are all 60" WMS-WMS!!

 

CW

Never said that their was. We were simply discussing if the MJ axle is the same axle as far as specs go to the CJ wide track axle. Simply looking for info to compare the code number to in reference to the plethora of info available on the AMC 20's found in the CJ's. If we could confirm that the MJ axle is essentially the same as the CJ wide track axle (besides the 2 piece vs. 1 piece shaft thing) it would make gathering info on the MJ AMC 20 a bit easier. Not to mention knowing if the aftermarket support for the CJ widetrack AMC 20 will bolt in to the MJ AMC 20 (aka alloy shafts, etc.). Unfortunately their is not a ton of info available out there on the MJ AMC 20 in reference to what was offered in what model, gear ratio's, code numbers, etc. The AMC 20 in my 2wd MJ clearly is not a metric ton package thing; showing once again that AMC/Chrysler/Jeep really had no rhyme or reason to anything. I was simply trying to gather more info on the axle itself found in the MJ's.

Your correct, YOU didnt say it... Hornbrod did!! :eek: :D

So you have the wide track version?

It was just a little rib at him. All in fun........

The the best of my knoledge and for our purposes here, there where two different AMC20's. Both ahd same dimentions, but different housings and axle shafts. As you eluded one was a two pices like the CJ's had and the other was a solid as conventionel axles are. It was put in a couple cars, lite trucks, and Jeeps.

Below is a copy paste from a JEEPTECH article: http://www.jeeptech.com/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

CW