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-   -   CJ7 Transmission Question. (http://www.jeepforum.com/forum/f8/cj7-transmission-question-1516496/)

DropeTine99 04-29-2013 08:37 PM

CJ7 Transmission Question.
 
I've got a 81 CJ7 that I want a 5 spd tranny in to get better MPG because I have the 4 spd. I found a AX-5 tranny but arn't they just for 4 bangers? And i read something about the T-5 only fitting 82-86 cjs? Any opinions on a tranny and how much of a difference it'll make to my MPG?

LumpyGrits 04-29-2013 08:42 PM

You'll NEVER will save enough gas to pay for the new box.
LG

DropeTine99 04-29-2013 08:48 PM

Well I'm running high rpms with the 4 spd so I wanted the overdrive gear to give my engine a break. I'm going to get headers and Electronic Ignition to help lower the rpms a little too.

firemanjim7 04-29-2013 08:57 PM

Quote:

Originally Posted by DropeTine99
Well I'm running high rpms with the 4 spd so I wanted the overdrive gear to give my engine a break. I'm going to get headers and Electronic Ignition to help lower the rpms a little too.

Unless you have long flat highways where you live you probably won't be using that OD gear anyways.

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LumpyGrits 04-29-2013 08:59 PM

You never said anything abourt "R's".:rolleyes: You only asked about MPG...
What size tires you run'n and what's your R&P?
What engine?
LG

DropeTine99 04-29-2013 09:05 PM

Alright, sorry bout that and i've got 33"s on 4.10s and the 258 6 cylinder. Never heard of the term R&P?

LumpyGrits 04-29-2013 09:14 PM

Quote:

Originally Posted by DropeTine99 (Post 15366433)
Alright, sorry bout that and i've got 33"s on 4.10s and the 258 6 cylinder. Never heard of the term R&P?

R&P = ring & pinion.:thumbsup:
What RPMs are you seeing at 65mph. TRUE 65mph. NOT what your speedo sez. You'll need a GPS for true ground-speed.
My '85 CJ-7 has 4:56 R&P, 33" BFG's and a T-5.
I start out in 2nd on the street and at 65mph in 5th. I'm run's 2550-2600rpm's
LG

DropeTine99 04-29-2013 09:34 PM

My tach stopped working but I top out somewhere around 60 mph, I'm guessing 2900-2800 rpms lol I went from a 2.73 R&P to the 4.10s and lost like 10 mph and some mpg. I don't get it lol Only thing I could think of was the tranny.

LumpyGrits 04-29-2013 09:43 PM

Get your tach fixed, then you will know for sure of what you are talking about.
The 4.2L, 6 cly. 'red-lines' at 4500rpm.
Your 'topping out' could be ign. timeing or carb. or BOTH.
My stock 6cly, 4.2L, 'pulls' all the way to red-line, and that is with 118K miles on it.
LG

DropeTine99 04-29-2013 09:46 PM

Alright I'll probably get another carb anyways. Thanks for the info! Now I gotta look into do either stuff

titomars 04-29-2013 11:36 PM

I have an '81 with a 258, T5 and 4:10's on 33X12.50's. I run about 2250 RPMs @ 65 MPH in 5th gear. My Cj came with the SR4 4spd.

It's a very simple swap since it was a factory CJ option.

DropeTine99 04-30-2013 04:59 AM

Quote:

Originally Posted by titomars
I have an '81 with a 258, T5 and 4:10's on 33X12.50's. I run about 2250 RPMs @ 65 MPH in 5th gear. My Cj came with the SR4 4spd.

It's a very simple swap since it was a factory CJ option.

How many Rs do you run in 4th?

LumpyGrits 04-30-2013 07:34 AM

Quote:

Originally Posted by DropeTine99 (Post 15367382)
How many Rs do you run in 4th?

See post #8 :thumbsup:

Neuner-9R 04-30-2013 07:47 AM

I have 33's, 3.31, T-5 and 258 and cruise down the fairly level highway in 5th at 65mph and at 1500rpm. After getting timing, plug gap and carb better tuned, it does fine against some incline and 20mph wind with room left to pass while still in 5th. Feels more like a diesel now with more lug. I go from 1st to 4th pretty quick.

Read all about the T-5 and its weaknesses. It's been doing alright but over the past year it's slowly been doing some strange things and I wonder how much longer before a rebuild.

titomars 04-30-2013 08:00 AM

Quote:

Originally Posted by DropeTine99 (Post 15367382)
How many Rs do you run in 4th?

I have no idea. I have never run it at 65 MPH in 4th gear.


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