Model 20 Axle Swap and Gear Change Help

Model 20 Axle Swap and Gear Change Help
Canadian CJ 7

Canadian CJ 7

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Current Setup 1985 Jeep CJ-258, 6cyl -T-5 5spd 273 gears.
In the next couple of months, I am going to be doing a one piece axle swap and gear ratio change in my stock Model 20 AMC rear end. I am also going to changing the Gear ratio in my Dana 30 front diff as well to match the rear end. I currently have 273 gears in both and it is non-posi. I am looking a getting Moser or Yukon axles and swapping in either 354 or 373 gears. My question, is it a straight forward gear swap from 273 to either 354 or 373? All you help and suggestions are greatly appreciated by me.

Canadian CJ7
 
You will need a new carrier in the AMC20 . not postive about the front, the break is 3:54 or 3:73 I can't remember for sure.
 
From my Limited knowledge of the AMC20 , all gears will work with all carriers... :)

The Dana 30 will need a carrier change... To be sure I would check - Yukon Gear & Axle - They have the most up to date gear info! :)
 
Old Dog said:
You will need a new carrier in the AMC20 . not postive about the front, the break is 3:54 or 3:73 I can't remember for sure.
Click to expand...
Trumps my knowledge! Just like a Dana 30 or a Dana 44 - you have to make a carrier change!
 
Hi Again, so I would need a carrier change for my Model 20 and Dana 30 differentials, if I changed my gears from 273 to 354 or 373. I have a wide track rear end (1985) would a narrow track carrier work with mine wide track or does it matter. Thanks for your help.
 
Canadian CJ 7 said:
Hi Again, so I would need a carrier change for my Model 20 and Dana 30 differentials, if I changed my gears from 273 to 354 or 373. I have a wide track rear end (1985) would a narrow track carrier work with mine wide track or does it matter. Thanks for your help.
Click to expand...

The AMC Model 20 carrier split 2.73 & down 3.08 & up.
The Dana 30 carrier split is 3.54 & down 3.73 & up.
 
Also the carrier can't tell if the housing is wide or narrow track.
 
Canadian CJ 7 said:
In the next couple of months, I am going to be doing a one piece axle swap and gear ratio change in my stock Model 20 AMC rear end. I am also going to changing the Gear ratio in my Dana 30 front diff as well to match the rear end. I currently have 273 gears in both and it is non-posi. I am looking a getting Moser or Yukon axles and swapping in either 354 or 373 gears. My question, is it a straight forward gear swap from 273 to either 354 or 373? All you help and suggestions are greatly appreciated by me.

Canadian CJ7
Click to expand...

If you want 3.54 you'll need one carrier, with 3.73 two carriers.
If your going to buy new carriers any way it's a good time to upgrade
to some type of traction adding carrier like a posi or locker.
 
what tire size are you looking at?, what engine size? if you are going over a 35" tire and have to change carriers anyway I would be thinking more of a 4:10/11 ratio. BUT that's just my opinion!!!
 
Hi again, I am going to be running 31X10.50 tires with a 2.5 inches of lift. The jeep is mostly going to be used for street use mostly and some trails. It will have a mild AMC 304 V-8 (cam, intake, 4bbl carb, exhaust) T-176 Transmission . It sounds like it would easier switching to 354 than it would be to 373. Any good lockers that are street friendly?
 
Canadian CJ 7 said:
Hi again, I am going to be running 31X10.50 tires with a 2.5 inches of lift. The jeep is mostly going to be used for street use mostly and some trails. It will have a mild AMC 304 V-8 (cam, intake, 4bbl carb, exhaust) T-176 Transmission . It sounds like it would easier switching to 354 than it would be to 373. Any good lockers that are street friendly?
Click to expand...

If your really tight on cash, it will work fine.
The 3.73 would be a rocket on the street though.;)
 
Canadian CJ 7 said:
Hi again, I am going to be running 31X10.50 tires with a 2.5 inches of lift. The jeep is mostly going to be used for street use mostly and some trails. It will have a mild AMC 304 V-8 (cam, intake, 4bbl carb, exhaust) T-176 Transmission . It sounds like it would easier switching to 354 than it would be to 373. Any good lockers that are street friendly?
Click to expand...


Knowing you will be driving in the snow and ice, and on the road, the only locker I would recommend is a selectable one ie air,elect,or cable. That way you have control of it and can turn it off.
A good limted slip would also be a good choice for the driving you said you will be doing.
Being able to have open-open is the best for ice and snow while on the blacktop if you like driving straight.;)
 
Locking both axles in snow and ice can be fun! An open diff is better... :)

As Old Dog said -(IMHO) a selectable locker is best for your conditions.
 
If I go to 373 gears with a stock T-176 , 4 speed and 31 inch tires, what do you think my cruising rpm would be at 50mph? Would there be a huge difference between 373 or 354 in take off (launching) and cruising rpm. Is it worth the extra cost going with 373 over 354? All you performance guys, I am putting this one out to you. Thanks again.
 
Canadian CJ 7 said:
If I go to 373 gears with a stock T-176 , 4 speed and 31 inch tires, what do you think my cruising rpm would be at 50mph? Would there be a huge difference between 373 or 354 in take off (launching) and cruising rpm. Is it worth the extra cost going with 373 over 354? All you performance guys, I am putting this one out to you. Thanks again.
Click to expand...

With a 3.73 gear about 2224 rpm.@ 55 mph.
 
For a 3.54 gear it would be 2110 rpm @ 55mph.
 
IMO if you drive in any hills I would do the 3:73. But as you say it will cost more.
If you never intend to go bigger tires and your a flat lander you could get away with the 3:54.
 
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