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What gears should I run

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Let me add two more recommendations.
1. get one piece axles for that AMC20
2. that T-5 is a light duty tranny. With an adapter you can easily put in a ford T-18 with a granny low.
I had an '82 CJ7 and that's what I did. The T-18 is normally intended to be started in 2nd gear. If you leave the stock gearing in the axles you can start off in 1st.
That would kill 2 birds with one stone: Re-gearing and getting rid of the light duty T-5 . That is the worst tranny to go into a CJ.
 
4.27 gears are not available for these axles (20/30). The decision is going to be between 4.10's and 4.56's. If you want really low, the 4.88's are there.

What plans for this Jeep? How much pavement is it going to see? Highway use?

Even with 4.10's, you are winding the AMC 258 i6 / 4.2l up pretty good at 65-70mph. My AMC 258 i6 / 4.2l always sounded like it was going to come apart on the freeway at those speeds, but with a redline of 4,500rpm's, that's what you get with the AMC 258 i6 / 4.2l *shrug*

I ran 4.10's with that exact settup and it was as close to perfect for onroad/offroad as you could get.

If you're strictly offroad, by all means go 4.56 or 4.88. A better option honestly however would be to drop in the 4.10's and if you want a lower final ratio, install a 4:1 in the Dana 300

EDIT: Is this a 6cyl or a 4cyl?
 
CJim7 said:
4.27 gears are not available for these axles (20/30). The decision is going to be between 4.10's and 4.56's. If you want really low, the 4.88's are there.

What plans for this Jeep? How much pavement is it going to see? Highway use?

Even with 4.10's, you are winding the AMC 258 i6 / 4.2l up pretty good at 65-70mph. My AMC 258 i6 / 4.2l always sounded like it was going to come apart on the freeway at those speeds, but with a redline of 4,500rpm's, that's what you get with the AMC 258 i6 / 4.2l *shrug*

I ran 4.10's with that exact settup and it was as close to perfect for onroad/offroad as you could get.

If you're strictly offroad, by all means go 4.56 or 4.88. A better option honestly however would be to drop in the 4.10's and if you want a lower final ratio, install a 4:1 in the Dana 300

EDIT: Is this a 6cyl or a 4cyl?
Click to expand...

The T-5 has an Overdrive that keeps your RPMs from shooting through the roof on the freeway. 4.56 gears wouldn't be unreasonable for a T-5 equipped CJ.
 
derf said:
The T-5 has an Overdrive that keeps your RPMs from shooting through the roof on the freeway. 4.56 gears wouldn't be unreasonable for a T-5 equipped CJ.
Click to expand...
Just talking from experience as I had the exact same settup....AMC 258 i6 / 4.2l /T-5 /Dana 300 , 4.10 gears and 33's ;)

Edit: At highway speeds, my rpm's were in the 3k's which is a lot for the AMC 258 i6 / 4.2l running extended periods. Couldnt imagine what the AMC 258 i6 / 4.2l would sound like at those speeds running 4.56 gears.
 
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CJim7 said:
Just talking from experience as I had the exact same settup....AMC 258 i6 / 4.2l /T-5 /Dana 300 , 4.10 gears and 33's ;)

Edit: At highway speeds, my rpm's were in the 3k's which is a lot for the AMC 258 i6 / 4.2l running extended periods. Couldnt imagine what the AMC 258 i6 / 4.2l would sound like at those speeds running 4.56 gears.
Click to expand...

That doesn't make any sense. Something in your setup isn't what you thought it was. Are you sure you had 4.10's? Did you shift into 5th gear? Are you sure your 33's were really 33" tall? Are you sure your tach was set up for a 6 cylinder and not a 4 banger?

At 65 MPH, 33" tall tires with 4.10 gears and a T-5 in Overdrive should put you just a little over 2300 RPM. Maybe 2400 if your 33's are a little short. 4.56's only take you up to 2600 RPM at 65.

Even with 4.88 gears, you shouldn't be hitting 3K RPM without 31" tall tires or shorter running a T-5 with Overdrive .

I could see if you had a T-4 without Overdrive . With that combo, 4.10s and 33's puts you over 2700 RPM at 65. Higher if your 33's aren't really 33" tall.
 
derf said:
That doesn't make any sense. Something in your setup isn't what you thought it was. Are you sure you had 4.10's? Did you shift into 5th gear? Are you sure your 33's were really 33" tall? Are you sure your tach was set up for a 6 cylinder and not a 4 banger?

At 65 MPH, 33" tall tires with 4.10 gears and a T-5 in Overdrive should put you just a little over 2300 RPM. Maybe 2400 if your 33's are a little short. 4.56's only take you up to 2600 RPM at 65.

Even with 4.88 gears, you shouldn't be hitting 3K RPM without 31" tall tires or shorter running a T-5 with Overdrive .

I could see if you had a T-4 without Overdrive . With that combo, 4.10s and 33's puts you over 2700 RPM at 65. Higher if your 33's aren't really 33" tall.
Click to expand...

Yep, yep, yep, and yep LOL!
I Know it doesn't make sense, because techically, 4.10's should have put me back in factory spec with the 33's.

I ran this Jeep for a lot of years set up like that and I always felt it was just a bit low geared on the highway at cruising speed. I always chalked it up to it being an offroad vehicle, not really meant as an interstate cruiser...blah blah.

This CJ originally was a 4cyl model which is equiped with 4.10's from the factory. I never swapped them out, but verified that that's what they were on several occasions (rebuilds, locker installs, upgrades, etc)
 
This CJ originally was a 4cyl model which is equiped with 4.10's from the factory. I never swapped them out, but verified that that's what they were on several occasions (rebuilds, locker installs, upgrades, etc)[/QUOTE]
Soooooo is the 4banger tach diffrent than the I6 tach? :confused:
 
With the 5 speed I'd go with 4:88's unless this is a highway jeep thats going to be doing 65 all the time.
 
gert said:
This CJ originally was a 4cyl model which is equiped with 4.10's from the factory. I never swapped them out, but verified that that's what they were on several occasions (rebuilds, locker installs, upgrades, etc)
Click to expand...
Soooooo is the 4banger tach diffrent than the I6 tach? :confused:[/QUOTE]

This CJ never didn't come with a factory tach. I installed a 6-8 tach.

BUT...before I go any further, I must apollogize. I've done so many swaps on this vehicle that I got a bit, shall we say, confused. Keep in mind, I've been modifying this CJ for almost 20 years...
Thinking back now, I believe I was probably running the T-18 when I was rapped out on the tach. :o

Looking back now from what I can remember between the alzheimers bouts...and knowing 5th gear is a 1:1 ratio, 4th was spooled out long before 65mph leaving me with a deadspot shifting into 5th. Once the engine built up torque again, it was good...but 65-75 was absolutely guttless.

Sorry for the confusing posts I managed to throw out there..that's not my style. I've been in this long enough to know better then to post tech without being positively accurate. :(

4.56 all the way :D
 
I agree with CJim7. That is if you have the Inline 6. I have the same set up. AMC 258 i6 / 4.2l , 33" tire, 4:1 tranfer case, and I am running 4.10s. Great all around gear.
Now if your not driving much on the highway then go with 4.56
 
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