Gear ratio ID - JeepForum.com

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post #1 of 23 Old 02-25-2010, 01:17 PM Thread Starter
Gallbladder
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Gear ratio ID

I have a ? year CJ that has an AMC 20 differential. The stamped number is supposed to be on the left side of the diff case by the cover. There is nothing there, but on the front of the rear diff at the top there is an "N" stamped on it. Is this the gear ratio Id? Thanks

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post #2 of 23 Old 02-25-2010, 01:27 PM
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It's stamped on the ring gear behind the cover !
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post #3 of 23 Old 02-25-2010, 01:34 PM Thread Starter
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Gear Ratio

I wasn't wanting to take the cover to ID. What does the large "N" mean on the front top side of the rear diff?
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post #4 of 23 Old 02-25-2010, 01:42 PM
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Originally Posted by Gallbladder View Post
I have a ? year CJ that has an AMC 20 differential.
You don't know the year of the CJ, so certainly you don't know when the fluid was last changed. Good time to flush. While you're at it, take a look at the gearing.

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I wasn't wanting to take the cover to ID. What does the large "N" mean on the front top side of the rear diff?
Nothing.
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post #5 of 23 Old 02-25-2010, 01:45 PM
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Originally Posted by Gallbladder View Post
I wasn't wanting to take the cover to ID. What does the large "N" mean on the front top side of the rear diff?
sorry to (sort of) disagree with Fatman, but an N stamped to the left side of a NT rear diff (like you should have in your '81) indicates it came with a 3.54 R&P with a trac-lok (from the factory)

if it is in fact, on top, then it stands for Nothing

Hoss

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post #6 of 23 Old 02-25-2010, 01:46 PM Thread Starter
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Good thought, thanks
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post #7 of 23 Old 02-25-2010, 01:49 PM Thread Starter
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Jon hoss, the "N" isn't on the passenger side. It is in the middle of the pumpkin on the shaft side at the top.
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post #8 of 23 Old 02-25-2010, 01:54 PM
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Jon hoss, the "N" isn't on the passenger side. It is in the middle of the pumpkin on the shaft side at the top.
who the HELL is jon???

hopefully, your axle has a shaft on each side

ok , seriously, on the flat boss where your axle tube slides into the diff housing on the left hand side, if you scrape away the crud, there should be a 1-2 letter code for what your Jeep came with from the factory.

What Fatman is trying to tell you is that the code won't mean squat if the gears have been changed, and that this is a good reason to service your Diffs



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post #9 of 23 Old 02-25-2010, 01:57 PM
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Originally Posted by JoonHoss View Post
sorry to (sort of) disagree with Fatman, but an N stamped to the left side of a NT rear diff (like you should have in your '81) indicates it came with a 3.54 R&P with a trac-lok (from the factory)

if it is in fact, on top, then it stands for Nothing

Hoss
Don't argue with me "John" I think he was refering to the big AZZ "N" on top.
Go back to your corner.
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post #10 of 23 Old 02-25-2010, 01:57 PM Thread Starter
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sorry joonhoos, thanks
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post #11 of 23 Old 02-25-2010, 02:07 PM
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Don't argue with me "John" I think he was refering to the big AZZ "N" on top.
Go back to your corner.
YouTube - Fat *** jokes



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post #12 of 23 Old 02-25-2010, 02:20 PM
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post #13 of 23 Old 02-25-2010, 02:50 PM
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OK. I am still a little confused. I have already powerwashed and degreased my rear axle. I will pop the cover off and ID my gear ratio that way in a couple weeks. Is there a stamp on the outside that will ID my gear ratio? I have a 77 with stock gears. Never changed. I see some numbers in different places, but they look greek to me.
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post #14 of 23 Old 02-25-2010, 03:00 PM
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Originally Posted by Daves77CJ7 View Post
OK. I am still a little confused. .. Is there a stamp on the outside that will ID my gear ratio? I have a 77 with stock gears. Never changed. I see some numbers in different places, but they look greek to me.
Jeep Axle: AMC 20



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post #15 of 23 Old 02-25-2010, 06:49 PM
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OK. I think I found what looks like an "A" with a circle around it near the top of the rear axle. I also found a tag on the front of my front axle differential that has some numbers that look like 3 54 ......

Based on the link that Hoss posted above, an "A" stamped on the rear would indicate the same as the numbers on the tag of my front axle. Looks to me like I have 3:54 ratio.?? All this time, I had assumed that my 77 was a 3:73.

Is 3:54 a good thing or bad? I will be running 33's with my T18 behind my slightly built up 258 (bored .40 over, Offy intake, Holley 4bbl, and Headers). What do you guys think of this combination?
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