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Discussion Starter · #1 ·
I am planning to put some beefier diffs in my Jeepster. I would like to up the front from a 27 to a 30 and the rear from a 30 to a 44. However, being new to this game, I don't know exactly what else has to be replaced (or should be replaced). I have been reading up and am not sure how to match up my axle ratios with my transmission and transfer case (stock for now). Thanks

Chris
 

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Look for a set from a '72-'73 Commando that's being parted out and you'll be set. Next choice would be a set from a '72-'75 CJ. 3.73:1 ring & pinion gears would be a good choice if you plan on staying with 31" or smaller tires. Both front and rear diffs must have the same gears. Tranny and transfer case gearing doesn't really factor into it. If you have manual 3 speed transmission, plan and save to replace it with a 4 speed SM-420 rather than rebuild it when it goes. It is a weak link. Also changing to a hydraulic clutch system from the cable system might be in order. TH-400 automatic is strong enough for a big block V-8, so if that's what you have, then not to worry. Another item of interest would be to convert to Saginaw manual or power steering, if your's is a '66-'69 and hasn't been converted from the Ross bellcrank system.
 

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Now, now. The AMC 20 ain't that bad. The ring and pinion are plenty strong. It'll work fine with one-piece axles. And if you bend the tubes, you can have them replaced with super-thick ones that'll last forever.
 

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A little axle stuff for ya!

The Dana 27 and the Dana 30 are essentially the same axle. The 27 is a 51" WMS to WMS closed knuckle while the 30 is an open knuckle. 30's come in several flavors ... Narrow track 53" drum and disc brake, early wide track 56" disc brake and late wide track 60" disc brake with vacuum disconnect.

The AMC Corporate 20 axle also came in different flavors. All had tapered axles in stock form. Replace them with 1 piece units The 53" CJ axles used a relatively thin tube that would bend or spin in the diff housing if they landed hard. I never had any problems with them because I always tried to keep to keep at least 2 wheels on the ground. Model 20's from wagoneers and trucks used a thick wall tube that was much stronger than the CJ's

A thick tube 20 with one piece axles is much stronger than a Dana 44 but the 4.56:1 is the lowest ration gearset available.

I can't find my axle shaft diameter and spline count chart but here's ring gear diameters for different axles

Dana 25 ...... 7.75" Obsoleter
Dana 27/30 ... 7.20" 27 had coarse spline axle/30 fine spline
Dana 28 ...... 6.63" Works in my AWD Aerostar
Dana 35 ...... 7.56" POS C-Clip axles
Dana 44 ...... 8.50" Good unit
AMC 20 ....... 8.88" Good unit if modded with thick tubes
Dana 60 ...... 9.75" Rockcrawler HD can't bust'em 350 pounders
 

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Okay Caver, I re-read my post and saw nothing about an AMC 20. Made a mention of a SM-420 though. If my data is correct, the AMC 20 materialized in the CJ's in '76, hence the statement for CJ axles from '72-'75. And what's wrong with shiney turds?
 

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Hey Rockcrusher,
Since it sounds like you got this stuff right off the top of your head,
Narrow track is 53"
Early wide is 56"
and Late wide is 60"

What was early/late Cherokee, Wagoneer, and J-trucks?
 

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Discussion Starter · #9 ·
I figured that I didn't have to worry too much about the xfer case and transmission for now (though I was debating a switch to at least a 4 speed trans). Thanks for the advice on donor vehicles because that was going to be my next question. Where is the best place to get an SM-420? Thanks again.
 

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Oh, Sorry for the confusion TIM....I was quoting an often used line from a well known TV show with Tim Allen "Home Improvements". I was referring to the link posted by LEE and was merely sharing MHO regarding the AMC20.
I my neck of the woods, every ******* from the age of 12 up knows they spin hubs, break shafts and spin (or bend) tubes. I agree that with enough work (read: $$$), they can be "just as good as a stock 44". How many folks do you know that remove a D44 to install a M20?
 

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Well, it just so happens that Punkin will have the flanged Dana 44 rear replaced with an AMC 20. I hate to do it after making sure my brother-in-law got a rig with a flanged 44. But we came on a deal for a D-30 front and AMC 20 rear from a CJ that have 4.10's, ARB's and Warn axles front and rear. Rear being full floater. Sorry I didn't follow your Tool Time train of thought. I tend to be a bear of very little brain.
 

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Discussion Starter · #15 ·
Hey now, I don't have a 20. And don't worry, I only put AMC parts in my vehicle if I want to make it ugly.
 

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Discussion Starter · #16 ·
What do you guys recommend as far as the adapter plate for the SM420? I think I know where I can get one, but I have read different things about the adapter plates on the board. It seems like the Novak is a little pricey, but if it is worth it as far as reducing the amount of crap you have to go through or reliability wise then I am willing to spend the extra dough. Thanks.
 

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Originally posted by GRQster

Hey Rockcrusher,
Since it sounds like you got this stuff right off the top of your head,
Narrow track is 53"
Early wide is 56"
and Late wide is 60"

What was early/late Cherokee, Wagoneer, and J-trucks?

RQ


Uh ... I dunno ... but they're too wide for my Jeepster.
 

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The fullsize Jeeps axle widths varied between the Wagoneer, Cherokee, Cherokee Chief, J-2000, J-4000, J-10 & J-20 pickups every couple of years. For example in '76:

Wagoneer - 59.4"/57.8"
Cherokee - 59.2"/57.8"
Chief - 65.4"/62.3"
J-trucks - 63.3"/63.8" or 64.6"/65.9"
 
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