3 spd or 4 spd

My 74 cj6 with 258 straight 6 is now completely disassembled. Frame is off the suspension. I have never driven this or any jeep. Since I am going through the entire jeep, should I keep the transmission (3 spd)? Or should I change it to a 4 speed? I'm am trying to make it an all around jeep. Some trail... some highway. Any suggestions on transmissions or gearing since I have this all apart?

 

From what you are saying the 3 speed would be fine. The 4 would be nice though. It all comes down to do you want to spend more $. The 3 speed would be free or nearly free if you had to rebuild it the 4 speed will cost you some money.

 

Which 4 speed would you suggest? Would it help on gas mileage?
Here are some pictures. I have a lot of body work to do.

 

Anyone would work but none will help with mileage because they all( except one obscure ford option) are 1:1 top gears.

 

Are you looking for better highway performance or better low range in the 4 speed?

For light to medium trail use I would say swap in a 4 speed but make sure it has an over drive for lower RPMs on the highway.

If you intend on hard trail use then get a 4 speed with a low first gear (wide ratio T-18 fits the bill nicely) for a better crawl ratio. This unfortunately wont give you an overdrive for the highway.

Modification is always a trade-off with these vehicles. To get better in one area you have to sacrifice another unless you are willing to spend major $$$$. And to make matters worse the short wheel base really restricts what you can make fit and still be functional.

 

One budget friendly option to consider if building an all around rig that has both good street manners and good general off road capability on moderate trails working with what you already have would be to keep the three speed as the 258 has enough power to pull in 4H and go with a lower gear set in the T-Case for a better off road crawl ratio in 4L.

You would not have to modify anything and it would all bolt back up exactly where it is now.

I agree that a 4 speed would be nice but if going through the expense of that conversion hudsonhawk has a good point about the overdrive.

 

you didn't ask this question, but what about a t5? it is a tiny little 5spd, will be great for your highway miles and i use mine for offroad only.

now, this isn't the choice transmission for a strictly offroad rig, but it is what i have and i use the hell out of it. if you are looking for gas mileage, overdrive, and more than 3 spds in a small tranny that fits in these little cj5's, these things are everywhere. also, if you look for one out of a later cj5, it may already be mated to a dana 300, which will give you an almost bullet proof t-case, with those lower ratio crawl gears. may not cost much to come across.

sorry, i don't mean to make it sound like you need to change your stuff, nor am i tryin to tell you to dump all kinds of dough-that's why i still have my t5; if i had the money and time, i'd go to a t18 for the strength and granny gear b/c my rig is strictly offroad.

***oh, and by the way, nice bike in the background in the garage!!!

 

Sorry but having built a lot of Jeep transmissions I could not in good conscience recommend someone purposely install a T-5 in anything. If it's there, fine, but that would mean a transfer case change or expensive adapter plus a different bellhousing. T-5 parts are getting harder to come by. 5th gear isn't manufactured any more nor are several of the other parts, and they are not a strong transmission to begin with.

Maybe an NV-3550 or something like that would be a best of both worlds but are looking at money. Has a decent low first gear but an overdrive too. Is fairly long but no issue in a CJ-6. Would require an adapter or transfer case swap though and a bellhousing and clutch change.

I'd say more info on planned useage, i.e. how much hiway vs. how much trail and type of trails would be helpful for a recommendation.
The transfer case gear swap idea is a good one. Another option would be a T-18 or something similar then have a more hiway friendly gearing in the diffs. Then you get decent hi way gearing, decent off road use with the low first gear, etc. plus a much stronger transmission then the T-14 that's there. A T-15 3 speed could be an almost bolt in option that would net a stronger transmission also.

 

ok, ok. i thought the t5's were everywhere. and ya, i did say not the ideal tranny for offroad. i did break mine before, thought it was the way i was driving. i was referring to this to being a much more highway friendly option, but absolutely seethe pain in the butt of swapping tcase and bellhousing if necessary. i was just throwing that option out there.

 

What axle ratio do you have? I used to own a CJ-6 with a 258/T-14/D20 and the standard 3.73 axles.

I like Nick's suggestion of the T-15. It's another 3-speed, but it is stronger than the T-14 you have now, and I like the ratios better. My main complaint about my 258 CJ-6 was the passing gear, or lack of one. The T-14 has a very low 2nd gear, so you can't downshift on long hills very well - either the Jeep is bogging down in 3rd or it's winding out in 2nd.

The optional 4.27 axle ratio would have helped too. If you have the means and the 3.73s, you should consider changing to 4.10 or 4.27 axle gears. I feel that the 4.27 ratio is fine on the street. With 3.73 gears, I would discard the idea of an overdrive transmission and think about how to get more gear reduction, not less.

The main reason folks change to the truck 4-speeds is for the granny gear. Every way to get lots of gear reduction costs money, and the granny gear is the most cost-effective to get that really high crawl ratio. However, since you've never driven this Jeep, I'd suggest you just put it together as it is and drive it. A factory-equipped CJ will go some amazing places...

 

You live in Chicago.
You have never owned a Jeep
I don't know how fast you work. But get that thing ready for spring/early summer and go enjoy it!
It is pretty easy to go back and make changes if you want to later. Jeeps are easy to work on.

Enjoy it on the street (without the top!)......Go on a few trail rides, maybe with a local club that does moderate trails,.....And THEN, figure out what you want to do with it.

Have Fun!

 

Thanks a lot for all the suggestions. I really appreciate it. I think I will repair the body, u-joints etc and take the suggestion of putting it together and driving it.

 

IMHO, the three speed is worthless for a rig that will see anything more than minimal, extremely easy, offroad use. The gearing is just too high. You can get the thing to work offroad, but a four speed will make it enjoyable instead of a major PITA and maybe a smoked clutch.

 

Good idea, because I've noticed people sometimes build a Jeep one way, and then end up using it another.