Where oh where is that AMC Model 20 I.D. tag??help - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-26-2000, 12:39 AM
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Where oh where is that AMC Model 20 I.D. tag??help

[img]/wwwthreads_images/icons/mad.gif[/img] [img]/wwwthreads_images/icons/mad.gif[/img] [img]/wwwthreads_images/icons/mad.gif[/img] Ok just got back from crawling around under my CJ and I can't find the ID letters to figure out my gear ratio. And i can't read the tag on the front. Can any one tell me where exactally this thing is supposed to be? Any one have a pic of this id thing? Thanks...Kyle[img]/wwwthreads_images/icons/mad.gif[/img]

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post #2 of (permalink) Old 08-26-2000, 12:49 AM
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Re: Where oh where is that AMC Model 20 I.D. tag??help

Every one I have ever seen was a thin stamped metal strip held between two of the differential cover bolts...

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post #3 of (permalink) Old 08-26-2000, 07:43 AM
 
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Re: Where oh where is that AMC Model 20 I.D. tag??help

Kyle,
My tag was also missing, this page will tell you where to look for a stamped reference and how to decode it.

http://www.off-road.com/jeep/tech/axle/amc20.html



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post #4 of (permalink) Old 08-26-2000, 10:23 AM
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Re: Where oh where is that AMC Model 20 I.D. tag??help

Kyle

If the stamped letter is defaced or been hit and you cannot see it , secure the vehicle and (this is if you DONT have posi or something) , jack up the rear SAFELY and rotate the rear wheel once and count how many turns the driveshaft makes. If you have a 304 , my bet is you have 3.54 gears.

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post #5 of (permalink) Old 08-26-2000, 02:19 PM
 
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Re: Where oh where is that AMC Model 20 I.D. tag??help

everybody says to raise a wheel and rotate the driveshaft. That really does not tell you anything, or there tell you to look for a tag or reference number, that really does not tell you if they been change. the sure fire quickest way to tell is to pull your cover and count the teeth, ain't no way to go wrong, beside you needed to change the oil anyway. It will take all of ten minutes and you will no for sure without going wrong. It is really easy

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post #6 of (permalink) Old 08-26-2000, 02:26 PM
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Re: Where oh where is that AMC Model 20 I.D. tag??help

[img]/wwwthreads_images/icons/cool.gif[/img] Yeah I think that iss what i am going to do any way. This way I can put a new diff cover on. Does the gas tank need to be removed before I can do all this? And what oil should I put back in? Thanks...Kyle

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post #7 of (permalink) Old 08-26-2000, 03:57 PM
 
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Re: Where oh where is that AMC Model 20 I.D. tag??help

According to the 1980 T.S.M. the rear axel is stamped with a letter designation code on the pumpkin boss just to the right of the dowel hole
.........letter.....ratio........pinion/drive teeth
standard...X.......3.07.............14/43
trac=loc...N.......3.54:1...........11/39
standard...A.......3.54:1...........11/39
trac-loc...Y.......3.07.............14/43


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post #8 of (permalink) Old 08-26-2000, 05:24 PM
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Re: Where oh where is that AMC Model 20 I.D. tag??help

Pulling the cover to count the teeth will work, but it is sometimes rather difficult to count the pinion teeth in this manner (you need both to divide for the ratio).

Jacking up the tire method does work, but I was pretty sure with an open diff you chock one tire so it cannot move, then you rotate the other tire 2 revolutions and count the driveshaft revolutions.

The reson for rotating the tire 2 times is that the spider gears change the effective gearing of the axle with one tire chocked in place.

This sound right to anyone else, or am I missing the boat here? [img]/wwwthreads_images/icons/crazy.gif[/img]

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post #9 of (permalink) Old 08-26-2000, 08:34 PM
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Re: Where oh where is that AMC Model 20 I.D. tag??help

On my 20 the letter is stamped on the passenger side of the diff. looking at it from the rear. I had to spray some cleaner on the diff and clean with a rag. It is very hard to see due to the fact it is only one or two small letters. Look between the cover and the tube.Btw, for some reason it was easier for me to find at night with a flashlight due to "shadowing". I looked all day w/o any results. Finally I got mad and went back out at 10:00 at night and found it right away! Good Luck. Chad

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post #10 of (permalink) Old 08-27-2000, 01:03 AM
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Re: Where oh where is that AMC Model 20 I.D. tag??help

I think if you pull the cover and rotate the gears you will find the ratio or the number of teeth for the ring and pinion stamped into the ring gear. just divide the the larger # by the smaller number to give you the ratio. You can also raise the vehicle, chalk the tire, chalk the driveshaft and rotate the tire(I've always had to rotate twice) and count the # of turns of the driveshaft i.e. 3 and 3/4 turns = 3.73. Sometimes you have to watch close to determine between 3.31 and 3.54 or 3.54 and 3.73 cause they're pretty close.
Bob

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