If I upgrade trans, do I have to upgrade the diff?

If I was to replace a t18 (4sp)with a t5(5sp) do I need to change the rear differential? Will it be a difficult swap?

 

No, you don't, but I have to ask, why do you want to replace a T-18 with a T-5?

 

As I'm not using my jeep off road any more, (only highway driving) I was hoping for better gas milage by having less rpms. Am I not correct in thinking that The t5 has a fifth gear and should be better on road? thanks for your replies.

 

To lower your RPM''s put on bigger tires. That's what we all want to do anyway......

 

I like the bigger tires theory. What is your axle ratio now?

How about an AX15 transmission? You can marry it up to your AMC engine directly - adaptation would be required at the transfer case. However, you don't need to change your rear axle.

You'd have to pull a T18 from my cold, dead fingers, personally, but I know the allure of overdrive.

 

Leave your Jeep as is and buy a used Yuppie Jeep(YJ) for the 5 speed and fuel mileage, thats why they made the YJ's.

 

thanks every one for your input, I'm thinking of going with the large tires and hope I don't roll over to often.

 

Big tires = more frontal area = greater wind resistance = higher fuel consumption too.

 

Jeeps=Bad Fuel ecomony.

I think the cost of any transmission swap will greatly outstrip any money saved from a small increase in fuel savings. By the time you get all the necessary adapters, probably a new clutch while you're in there, correct the driveshaft legnths, etc etc... You'll spend alot of money for 3 or 4 mpg increase.

 

Larger tires = possibly running the engine in its optimum zone, which can have a significantly positive effect on mileage. And, you don't have to go heavy and wide with them. Heaver rolling mass will not hurt you during cruising speeds, but do have some effect during accel/decel.

The taller aspect of the Jeep pushing through the wind is a factor, but I think running the motor at optimum will overrule all of the above considerations.

Eric