Gearing recommendations

Living2Learn

New Member
Joined
Apr 19, 2024
Location
Cary, NC
1984 CJ7 - Rebuilt 258 with EFI. Dana 30 front, AMC20 (3.31 stock gears) rear with 1 piece axles. 3" lift with P285/70R17 (32.8")

The short of it, my rear pinion seal is leaking and my confidence that the preload is set correctly...pretty low.

I mostly use my Jeep around town, because I'm not sure it would make it to Uhwarrie and back, around 55 miles since 2022. Having said that, as I get more comfortable with my own abilities to do more repairs, I'm interested in driving longer distances. Gas milage has been, meh, but with a broken gas gauge it's not been easy to tell.

I was thinking 3.73 would be a good swap, but the more I've been reading, going to 4.10 might be better? I would like to attempt this myself, but by far be the most complicated work I've done before on it.

I believe I would also need to swap the Dana 30 to 4.10 as well? Is there enough axle droop on the rear for access, or will I need to drop the gas tank as well?

Thank you for your time.
 
You have to swap both axle gears to the same ratio at the same time.
4.10 is the absolute minimum Id go and I'd probably leaner lower. Off top of my head I don't know the limitations on the 30/20 or the carrier breaks if any.
@Jody Treadway among others could advise here better.

Without knowing you or you skill set and toolset...but reading between the lines of your post, if you can find a set of take out axles already geared to your liking its most likely something you could do yourself.
If you are having to regear your axles....that is a fairly advanced complexity repair. And requires specialized tools that if you arent planning on doing it regularly - you probably end up cheaper and better to pay the man.
 
I agree with @Ron here.
Gear work isn't for someone that's just dabbling in car repair. But, it can be done, for sure.
I stick with my 4.56 assessment. I had a cj7 with a 258-T5 combo with 4.56 and 33's. It was great.
 
Thanks for the input guys. I am pretty committed to attempting myself. Going to go to the next CNC4x4 meet up when it rolls around. I'm hoping to find someone in my area that can help me if I get in a pinch.
 
You will need to gather up the following tools if you don't have them.
Torque wrenches in foot pounds and inch pounds.
Dial indicator and mag base.
0-1 micrometer or at least a dial or digital caliper.
Dummy bearings are really helpful.
You may need a case spreader, but back when I did gears I really only needed it for the larger axles (Dana 60-70).
@Jody Treadway hopefully can chime in since he does gear swaps on a regular basis.
 
Living2Learn said:
Tom,
What did you mean by "Not much of a pinion in a Dana 30 with 4:56 ratio though." ?
Click to expand...
The d30 is a smaller axle overall.
When you get to a 4.56 gear to get that many teeth on the pinion head there isn’t that much material left.

Wish you tons of luck with the gear setup.

Not trying to be discouraging but r&p setup is like graduate level mechanics. Lots of professional mechanics take their personal regears to specialty shops.

And not trying to be derogatory but by some of your questions seems like you are more entry level/learning on your jeep work.

It would be akin to asking an elementary school math student …just skip algebra and geometry, let’s go right to senior college level calculus with 3 variables.

It’s nothing impossible that you can’t pull off. You will just need to buy tools that will cost you more than paying a pro to do it and those tools really aren’t used for anything but setting up r&ps. And if you don’t get it right…well at a min you will be buying more bearings more likely a new gear set.
 
I have 3.73s with mine on 31s and am very happy. I’d like to step up to your current size tire with my same gears and I bet I’d be more happy on the highway
 
I ran my 85 cj7 with 4.56:1 gears and 35's for a couple years. Had the Mopar multi port efi and all the goodies on the 258 and the T5. It would hardly do 70mph and couldn't keep hwy speed on hills. So I'd definitely target 4.56 over the 4.10's.

Better yet look for a set of axles that have already been geared and give you more strength over the CJ stockers. Wagoneer axles are a nice width on a cj, but factory gearing was pretty tall.
 
Clubbs said:
I ran my 85 cj7 with 4.56:1 gears and 35's for a couple years. Had the Mopar multi port efi and all the goodies on the 258 and the T5. It would hardly do 70mph and couldn't keep hwy speed on hills. So I'd definitely target 4.56 over the 4.10's.

Better yet look for a set of axles that have already been geared and give you more strength over the CJ stockers. Wagoneer axles are a nice width on a cj, but factory gearing was pretty tall.
Click to expand...
Or 4cyl YJ axles are a 4.10
 
Monkeynono said:
Or 4cyl YJ axles are a 4.10
Click to expand...

Yup, but isn't the front diff on the wrong side for a cj?

I prefer 1 tons.

Leaf springs and 1 tons on an old CJ stretched with xj rear springs and waggy front springs is old school legit
 
You'll want 4.56 ratio with that set up. No worries about pinion strength given the powerplant and intended use.
Hopefully the CNC guys will have a big array of tools and equipment needed to install them. It's not rocket science. But 0.003" makes a difference between right and wrong.
Good luck dooder
 
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