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Unread 02-06-2014, 10:59 AM   #1
BiscuitTX
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1985 CJ7 
 
Join Date: Sep 2012
Location: Houston, Texas
Posts: 57
G 85 CJ7 Automatic

I have an 85 CJ7 3 speed auto. Large tires (33's) have slowed this bad boy way down and eats gas to the tune of 7 MPG. Does anyone happen to know whether an 85 automatic has a 2.73 or a 3.73 gears? Presumably the best thing to do would be upgrade to a 4.10?


thx

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Unread 02-06-2014, 11:53 AM   #2
wm69
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Join Date: Jun 2003
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Probably have 2.73's. Look at your rear axle housing and see.....
axle-code.jpg   amc20-gear-ratio-1.jpg  
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85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 02-06-2014, 12:53 PM   #3
dandd
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1982 CJ8 
 
Join Date: Oct 2012
Location: San Jose, California
Posts: 64
I have a 82 with auto and 4.11 gears and 35's. If there is minimal freeway this setup is good. At 65 mph I'm at 3000 rpm's. This is due to about a 200-300 rpm increase from the torque converter slip (non lockup). For offroad use I have a crawler box which gives me a total of 90:1 ratio to the rear wheels. If I had to do it over I would put in 3.73 or 3.9 to get lower freeway rpm's. This is a cj8 with a weight of 4150 lb's and I get 10-12 around town and 14-15 freeway.
Without a crawler box or low TC gears I would think you need to prioritize either more trail or more road. My rear had 2.73 gears originaly.
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Unread 02-06-2014, 12:56 PM   #4
BiscuitTX
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1985 CJ7 
 
Join Date: Sep 2012
Location: Houston, Texas
Posts: 57
Quote:
Originally Posted by wm69
Probably have 2.73's. Look at your rear axle housing and see.....
Which one is which?
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Unread 02-06-2014, 01:54 PM   #5
wm69
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Well what do you have stamped on your housings where the above pictures indicate?

Likely D, DD, B or BB on an 85

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
__________________
85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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Unread 02-06-2014, 04:23 PM   #6
BiscuitTX
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1985 CJ7 
 
Join Date: Sep 2012
Location: Houston, Texas
Posts: 57
Rear axle housing has DD so 2.73 explains the lack of power and gas guzzle. Thanks for your help.
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