gears??

[littlechief]

Hi all, new here but looks like a wonderful place to visit. Also new to the FSJ scene, just bought my beast before christmas. Have done a bunch of work to her so far but still so much left to do. Trying to figure out what gears that I have, whatever they are they're too tall. Its an 81 cherokee chief with the 360, 4 speed t178, np 208 tc, amc 20 rear and dana 44 front. Am planning on swapping gears in her this winter and would also like to add a locker. Currently I am running 33" swampers on her. Wondering if anybody can tell me the gears that are in her now and what gears that I should swap to. I am looking to be able to crawl a lot slower, also would like to go to 36" tires. Any thoughts or suggestions would be greatly appreciated.

[SpruceMoose]

is there a factory tag on either diff? it should be on the cover on the 44, not sure about the 20. if not, jack up one end, in neutral(block the other end!) and turn the tire one rev. count the driveshaft revs. theres your ratio!

[littlechief]

it does have a tag on the front but there is 2 sets of numbers on it, not sure what they mean, will have to get the numbers then post back here. Thanks for the revolution idea Spruce smile.gif all things are simple once you know eh?

[Veepster]

same general idea as Spruce said..........but if you have the cover off count the teeth on the ring gear and divide by the number of teeth on the pinion gear....

[bchesley]

I have a set of 4.11 sitting in my garage waiting to be installed. I will be turning 3000 rpm at 70 mph with 33" tall tires. This is a little higher than the factory tow package and stock tires. I would say that the optimum would be any where from 2700 to 3000 rpm would do fine at 70, any lower and you would lose drivability (is that a word?).

Brad

[ibnfe]

4.56 gears and 35" tires will give you 3000 rpm at 70 mph. There is a formula to figure out your highway rpm and allhere (http://www.mgbexperience.com/misc/tirecalc.html). 4.11's will probably give you the most versatility if you plan on doing a decent amount of offroad. If not, then maybe 3.73's. If you want really low rock crawlers, go with the 4.56's.

[jeepbob]

Couple of things about the formula, you must measure the rolling dia of your tires as they are on the truck to get the true size and there is no allowance made for torque converter slip.

Littlechief I know you have a manual tranny so this will not affect you, but those out there that think you will only be running 3000 rpm with 33's and an auto, guess again, it is more like 3400 - 3600 rpm. I have 33's and built T400 and try to avoid the highway as the motor is a crankin. if you do a lot of highway driving then 3.73's would be a better choice for 33's. 4.56 would be a good choice for a manual and 35's or 36's

[jeepers]

Since we are on the topic of gears and ratios how much difference is there between 2.73 and 3.73 on takeoff when pulling weight?

[ClarkGriswald]

Let me just say .. 2.72's NEVER should have been installed on a jeep..

Feels like your taking off in high gear all the time.. very boggy..

[ibnfe]

2.72's are for camaros and such other 2000 lb cars, not a 3 ton truck like ours! 3.73's should have been the standard, along with a slightly higher stock ride height and larger tires. But of course, this is the opinion of a non-highway lover. I still refuse to take the interstate if I can use side roads or dirt roads, or better yet, overgrown from lack of use trails.... :D