gear swap

I have a 63 CJ5 all original powertrain. I recently lifted the truck and i'm running 32" tires. The vehicle is used strictly off road and spends 90% of it's life in 4 low. Now that I'm running the larger tires I've lost some of my low end grunt and crawling capabilities. My question is what is the best way to gain some low gearing without breaking the bank? Should I just swap ring and pinions? I could swap gears in the transfer case but I beleive i have the small hole Dana 18 so I would need to get another case. What about swapping gears in the transmission? Would that produced the desired effect. I am not at all concerned about cruising speed RPM. The vehicle is used for plowing and wheeling only. Thanks

 

'63 with F-head and T-90 could have 4.27-1 axle ratios but optional was 5.38-1. If you have 4.27's now then a switch to 4.88's or 5.38-1 would be a big improvement. Seems like I've seen far mor 5.38-1's in this vintage Jeep than 4.27-1. Like BKD asked, what ratio do you have now?

 

Not 100% sure what gears I'm running right now. Can I tell throught VIN decipherment? The vehicle is not with me right now

 

VIN won't tell you how it's optioned out. Need to look at the tags on the axles, pull the covers and count teeth/look at id #'s as the tooth counts are usually stamped in the ring gear, or jack it up and turn the drive shaft and count the turns until both tires make one revolution.

 

Thanks guys. I'll check out the axle gear ratios this weekend.

 

Like nickmil stated 4.27 was the service standard for 1963 but 5.38 was an option.
Most all post 1962 pre 1972 CJ's wiith 4 clyinder engine were equipped with the 4.27 final drive ratio.
The lowest final drive ratio you can bolt in will be the 5.38 gears that were commonly used prior to 1963.
If you have the standard 1963 drivetrain your T-90 C transmission will have the desireable 3.34 to 1 first gear ratio.

3.34 (transmission) x 2.46 (transfer case) x 5.38 ( final drive) = a crawl ratio of 44 to 1

 

I thought the same Patrick as my experiences have been the same as yours but I looked it up in the FSM. It shows 4.27 as standard and 5.38 as the option. I would have thought the opposite. Apparently a LOT of people ordered 5.38'sR)

 

Regardless of whether I have 4:27 ot 5:38s, is an axle gear swap my best choice for reclaiming a good crawling gear? I could swap out transfer case gears ($800 plus a different case with a big hole) or what about swapping out transmission gears? Can you get different gears for the T90? Is an axle gear swap going to be the most efficient and least costly way to get what I want?

 

If you have 4.27s, a 5.38 axle swap could be cheap and easy. Axles for these vehicles are not in great demand, and the 5.38 axles are common. Replacing gears would be comparatively expensive and exceeds the capabilities of most amateur mechanics. 5.38/4.27 = 26% lower.

There is a T-90C with slightly better gearing. You may already have it though. 3.34/2.79 = 20% lower in 1st gear.

The T-98 transmission used with the F134 would give you a much lower 1st gear. Scarce and generally expensive if you find one. 6.32/2.79 = 127% lower in 1st.

Tera gears for the T-18. You know the story there. 3.15/2.42 = 30% lower in low range.

You could combine the axles, T-90C and Tera gears to get 1.26*1.20*1.27 = 92% lower in 1st, assuming you now have the T-90A.

In order of expense, it's likely axles, T-90C, Tera gears, and T-98.

In order of difficulty, it's likely T-90C, axles, Tera Gears and T-98.

 

If that's true then we're all really lucky to have the rare 5:38's.R) I've only found one set of 4:27's out of many many early's I've seen

 

The final drive ratio change was implimented in conjunction with the transmission change.
http://www.film.queensu.ca/CJ3B/Photos/Tech/ServiceBulletins/SB601AxleRatio.JPG
http://www.film.queensu.ca/CJ3B/Photos/Tech/ServiceBulletins/SB600Tranny.JPG

I agree with Tim Reeses excellent remark.
However I believe its probably easier to swap in complete axle sets and bleed brake lines rather than remove then replace a transmission.
Swapping between axle sets allows reasonable versatility.

 

It's very relevant whether you have 4.27's or 5.38's. If you already have 5.38's you simply can't go any lower in the axles you have, period. If you have 4.27's then you can go lower and as Tim's excellent post pointed out it's a significant change. Which way to go monetarily can depend greatly on what you have now. I'd find that out first then go from there.

 

Thanks to all for the great insight. I'll check the axle gears and go from there. That's what you have to love about these projects. Every improvement creates a need for another....