CJ7 258 Trans Swap

[jakenmiss]

Hi All,

New to the CJ world - Just picked up a 76 CJ with a 258 and T18 with Granny gear - Up and to the right is Reverse..

I picked it up so we could have a project to work on with my 16 year old son. so it should be fun.. Before I get started to far down the rabbit hole I could use some advice from the experts, or at least more knowledgable then me.

Driving the Jeep home the other day I noticed that I had a real hard time getting over 50 MPH in the jeep. I dont want a drag racer or highway runner but I was hoping that it would keep up with traffic on the back roads so he could take it to school some times or we could use it to run errands and such.. I dont expect to do a ton of 4x4 just wanted a simple old jeep to work on.

The guy before me put 35's and upgraded the axels. I am just wondering if there is a good simple trans swap that I could look at doing that would improve the on road capabilities. It looks like AX15 or T176/177 might be the best bet but I wanted to get some opinions laid out before I start opening the old wallet up too far.. Thanks in advance for the help.. Looks like alot of good stuff on here and I could probably get easily overwhelmed.. - Jake

 

[Belizean]

What is your gear ratio / ring and pinion in your 2 differentials ?

 

[coldair]

I run an AX15 in my cj. Its a pretty easy swap but not sure it will help you with your top speed if your axle gearing is high.

 

[jakenmiss]

Thanks - Guess I need to do some digging and figure out what the guy before me put in there. I am guessing its pretty high..

 

[coldair]

What speeds do you plan on running with this jeep? I can run max 75 in mine but thats as fast as it will go with the gears and tires i run. BTW I don't recommend running that fast in a jeep unless everything has been rebuilt and gone over more times then you can count.

 

[jakenmiss]

I just want to be able to run on the roads - 45-55.. Right now I get a huge back up of traffic and the other day really put it in a bind going down hill for long distances.. I think I am topped out at the speed right now and it sounds like I could use a few more gears to lessen the RPM's on the old engine.. I was hoping a trans swap would be good but I will research what the differential ratio and see what happens there.

 

[coldair]

I just want to be able to run on the roads - 45-55.. Right now I get a huge back up of traffic and the other day really put it in a bind going down hill for long distances.. I think I am topped out at the speed right now and it sounds like I could use a few more gears to lessen the RPM's on the old engine.. I was hoping a trans swap would be good but I will research what the differential ratio and see what happens there.

If you're needing lower rpm an AX15 will help with that.

 

[RiverandSand]

Also those 35s are alot of tire and if its poorly geared thats compounding the issue. You want no less that 4:11s and 4:56s would better for that much tire.

 

[coldair]

I run 4.88 gears with a almost true 33 tall tire. I wont break any land speed records but it does what I want it to do.

 

[RiverandSand]

I run 4.88 gears with a almost true 33 tall tire. I wont break any land speed records but it does what I want it to do.

What are you turning for rpm on the highway? I really haven't had mine much above 60 since it's been back on the road, it was turning 2200 @ 60 with 3:54s on 33s. Of course this all subjective as I really don't know if the gauges are accurate.

 

[coldair]

I have to check the calibration of my tach before I can tell you for sure.

 

[JR74CJ5]

With 33's, and 4.27 gears, I'm running about 3100 - 3200 RPM @ 75-80 MPH iirc.

The gearing and tire size ratio is important for your acceleration abilities.

The gear ratio itself is important for your top speed ability.

A sweet spot in the middle of either would be best.

Trans swap wouldn't help unless it has a overdrive. All final gears are 1:1 unless overdrive (which Coldairs suggested AX15 does)

FYI, that trans you have is gold - don't let it go dirt cheap. Research it, crawlers like me love them and the bell housings / adapters for rock crawling for that very low granny 1st.

What does your son want to do more with it? If he's into off-roading, or might be later, I'd look into leaving that trans and tire set up, and looking at the gearing changes possibly.

Also, just in case - you're sure you were not in low @ the transfer case right? No disrespect - just asking...

 

[JR74CJ5]

Lot of good info here on Trans swap options etc

https://www.novak-adapt.com/knowledge/transmissions/

 

[jakenmiss]

Thanks Gents,

I will check on the transfer case this weekend.. I thought of that last night as well..

Appreciate the advice.. I will come back later when I actually figure out what I have underneath :-)

 

[JimsCJ5]

If your 16 yr old will be driving it I would suggest ditching the 35's and bringing the height down to stock. You can always jack it up again after he has some experience/hours behind the wheel.
Our 258/t18/3.54/ stock wheels combo will cruise along fine at 65 mph and is a great local roads driver.

 

[Lumpy Grits]

Stay with that T-18. It's a tough tranny.
You must find out what the R&P ratio is.
What axles did this PO upgrade to?
Can you post pictures?
Look at 32's or 33's for tires.
Does this Jeep have a tach in it?
If not-get one so you know what RPM's you're run at say 50mph.
LG

 

[jakenmiss]

Thanks Gents,

Going to look at smaller tires right now so we can at least enjoy it while I look at the other options I have heard about.. I do need to get a Tach for it for sure as all I am going off is sound.

I will post pictures as I keep moving forward.

Appreciate the help..

Jake