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Unread 10-19-2011, 06:27 PM   #1
tb77
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Grear ratios

Hi I'm new to the forum I have a 85 cj-7 256 weber carb 32" tires I swapped out the junk Tf-999 tranny with a t176 4speed gears 1 thru 3 drive pretty good but 4 th is awefull on hi way very hard to maintain rpm for that gear I think stock gear ratio is 2:something I'm thinking 3:73 does anybody have usefull input thanks

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Unread 10-19-2011, 06:36 PM   #2
BioTex
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Probably has 3.31's.
What are your intentions with the Jeep?

Edit: Good choice on the new tranny, and welcome!
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Unread 10-19-2011, 06:43 PM   #3
tb77
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Thanks, light offroading cruising around town hiway to get to work when it's nice mostly a toy to work on with my 5 year old son
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Unread 10-19-2011, 07:13 PM   #4
keith460
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For 1985 stock gears with the 258 engine were 2.73 and an optional 3.31.
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Restoration Thread:http://www.jeepsunlimited.com/forums...d.php?t=434226
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Unread 10-19-2011, 07:42 PM   #5
tb77
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What would be a good ratio to fix my 4th gear problem
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Unread 10-19-2011, 08:10 PM   #6
keith460
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With 32" tires, 3.73's or a little better on highway with 3.54's.
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Unread 10-20-2011, 09:27 AM   #7
PavementPounder
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I doubt he has 3.31s if he can't maintain highway speed with a 1:1 4th gear with 32" tires. Sure sounds like 2.72s.

I ran 31s with 3.31s, a 258, and a T-5 for years and got excellent mileage with sufficient power to hold 70mph in 5th until I ran into the occasional really long incline (like on I-80 in PA, etc). The key here is really engine health. You don't want to re-gear to compensate for a tired motor. Numerically, I think 3.73s might be overshooting the goal, as I don't think you should be having quite as much of a problem as you are having with the current configuration. If you are dead-set on swapping gears, I'd limit it to 3.54 and investigate your motor. You have a Weber carb, but perhaps it is not optimally tuned. There's also a lot you can do with 258 ignition systems and bolt-in parts to help it breathe easier.
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Unread 10-20-2011, 10:20 AM   #8
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It sounds like he's got 2.73s to me, as well.

tb77, assuming you have a stock AMC 20 rear axle, there should be a 2-letter code (like AA, BB, CC etc...) stamped on the right side of the pumpkin, near the axle tube. That will indicate the gearing. You'll have to look up the chart once you find the code.

I'm running a 4-speed on 32"s with 2.73s and I'm in the same boat. 3rd gear is reasonably strong between 35-55 mph, but 4th is doggy unless I'm on flat terrain with a tailwind. My engine has good compression and oil pressure. It also has a new "Team Rush" ignition and Weber carb, both of which are tuned well.

My tranny is the S4, which oddly is holding up well, but I hope to replace it with a 5-speed and either 3.73 or 4.10s when the S4 decides to fail me. I can live with getting passed on the highway until then.

Matt
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Unread 10-20-2011, 12:24 PM   #9
mtnbikeidaho
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Quote:
Originally Posted by keith460 View Post
With 32" tires, 3.73's or a little better on highway with 3.54's.
Keith- First off, love your rebuild. Amazing amount of work went into that project.

If I recall, you are running BFG 32's and a 4.10 ratio?? Just curious as to why you recommend taller gears for the OP. Is the 4.10 a little too low for highway use? (Maybe not suitable for a 1:1 tranny but ok for an overdrive T-5??)
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