4speed tranny

what whould the benifits of changing a t15 to a t18 tranny into a 74 cj-5 304 373 gear

 

The big benefit is the lower 1st gear. Another benefit is a stronger transmission ( although the T15 is a fairly strong unit).

 

any fuel usage advantage

 

Like Don says...
But I don't figure that strength is a big issue.
The T15 weighs 75 lbs with a 3/1 reduction.
The T18 weighs 160 lbs with a 6.32 reduction.
The reduction is just over double.
The weight is just over double. Do you get the idea ?
Mass = strength divided by the reduction ratio.
Granted its a crude formula but they come out about the same on strength.

By the way those are certainly two of the best Jeep transmissions ever.

 

Nope. Not unless you change your axle gears and then it will cost enough that you won't be able to make that money back for a long time.

 

I wouldn't swap unless I was trying to run 35's or bigger tires.

 

X2 without a doubt the best mod I have done to the jeep.

 

Here are two pics showing the difference between the T-18 and T-15. Not sure how well you will be able to see the difference in size/strength between the T-18 and T-15 but the gear size and strength is much better/larger on the T-18. They also don't wear the dog teeth on the gears near as bad. Having said that, the T-15 is the strongest of all the 3 speeds Jeep used and is a decent transmission. Just no where near as strong as a T-18, nor is it meant to be.

 

x3-- the T-18 transmission is a wonderful piece of engineering. I put over 100K miles on mine. There's nothing quite like the feel of a top-loader granny tranny.

 

I went from a T150 to a T18 behind 3.73 gears, 31'" tires and a 304. The T150 actually blew out, so I had to get a replacement and I thought....why not. One of the 2 best mods I have done. The other being power steering.

The T18 runs on the street just like my T150 did, even the respective 4th and 3rd gears being 1:1 so they even feel the same. The 1st gear in the T18 is not syncronized and is way forward making its use really a trail-only type situation. On the street I use a 2nd gear start. I have found that after the T18 install I almost never go into 4L anymore....just don't need it.

 

If you notice any fuel economy difference, it should get worse with the T-18 swap. More weight, more friction/inertia from the heavier gears. Probably so small a difference it'll be hard to measure over a short time though.

But still, it's worthwhile. 3.73:1 is long-legged for a Jeep. The low first gear is a great thing.

If you want better fuel economy, I suggest you run narrower tires at higher pressure, keep the engine in tip-top tune, and keep your speed down.

 

I have bought my jeep with the t18 in it....3.73 runing with 33" it's fine and all my friend riding with me ask me why i got this amount of gear. Having 3.73 gear in the axle give you a bigger gear so more strenght and provide you a very good fuel economy. I have at the moment 3.07 gear, if someday i buy a low range 3.xx:1 for tha dana 20 i will put 3.07 in the axle for a better fuel economy. The best of two world....good low range and a good fuel economy on the road....

 

I too upgraded from a T14 to T18 and absolutely love it. It is nice to have the ability to have a wicked crawl ratio (84:1) and still go down the road, though my jeep doesn't do much of it!

 

The best thing I have done to my 75 CJ5 is to install a four speed with a 6:32 granny gear.. If I could only do one thing to my Jeep it would be the granny gear 4 speed..

 

I sometimes have to give mine gas to keep from sliding it engine brakes so well.

 

yep, lower gearing, my first stab was axle gears, then the granny tranny, and then finally a doubler, ended up with nearly 175 to 1 crawl ratio, stupid low, and only useful in limited use around my neck of the woods, but made trail riding and crawling easier and more precise in effort

 

Doubler in a cj5?

 

I'll say like you a doubler???? any pic of that?