What's the correct gear?

[Louisianajeepn]

I know this is probably on the forum somewhere but I have been looking for awhile and can't find exactly what I'm needing to know. This is my 1st jeep and i am hooked, i will always have one now! I have a 2003 Tj sport automatic transmission with 3:73 gears from what I can make off the tags on the diffs. Dana 30 and 35. I have a 4 inch suspension lift and a 3 inch body lift. The jeep is running 35 bfg ko's. I want to regear it to be similar to stock. Mabey a little lower but not much. It is a weekend vehicle and spends most of the time running down the hwy. mud riding on occasions and going to the beach. It will never see rocks(we dont have many rocks where i live, plenty of mud though) Not too worried about fuel mileage but it is doing horrible right now. I would like to be able to run down the hwy at 70mph with out having to turn off the overdrive or turning 4000rpms. I want to take the strain off the drive train. What would be the best suitable gear that I should run? I've been told 4:10 and 4:88 from different people. Any help would be greatly appreciated

Thanks in advance

Danny

 

[Shephard10]

I'm not good with gears, but I would say between 4.10 and 4.88. I would probably go with 4.56...

Glad to see a new Louisiana jeeper!! Where ya from?? I'm out by New Orleans.

 

[Louisianajeepn]

I'm not good with gears, but I would say between 4.10 and 4.88. I would probably go with 4.56...

Glad to see a new Louisiana jeeper!! Where ya from?? I'm out by New Orleans.

I live in larose 70373. About an hour from Nola

 

[Trailmaster]

From what I have read you want 4.88s, I'm going up to 35's myself and plan to go to the same.

 

[ralavoie_417]

4:56 Is the ratio you want. My jeep has 4:88 on 37s.

 

[0III0forlife]

4.56 is the ratio that u want. i have an '87 YJ with 8.5 inches of lift and 35" tires. with 4.56's i turn about 2500 rpms in 5th gear on the interstate at 70 mph. 4.10's will be too high of a gear for the auto, and 4.88's will give you good gears for in the mud but it will be wanting another gear when out on the highway.

 

[69jeepcj]

There is a formula for finding this. Google gear ratio formulas, there is one for final low range gear ratio, one that will tell you what rpms you will turn at a certain mph. If you have a 6cyl, I would think 4.56.

 

[69jeepcj]

A simple formula

The most simple formula for the correct gear ratio is this:
New Tire Size x Old Gear RatioNew Gear Ratio =―――――――――――――――――Old Tire Size
Example:
The original tire size is 30" and the original gear ratio is 3.91. You plan on moving up to 38". Then the formula would be calculated as: (38*3.91)/30 giving you 4.95. Not all gear ratios are available so you have the choice between 4.88 and 5.13, 4.88 being the closest.
Choose a little bit lower gear ratios if you do a lot of off-road driving and a little bit higher if you do more long distance highway trips.

 

[littlesdrag]

I have a cj5 with 33's wanting to end up with 35's. How would you fig in that I only have a manual 3 speed.

 

[69jeepcj]

littlesdrag, I came up with 3.75. I would say 3.73 or 4.10 gear, if you have a v-8 id go 3.73, 6cyl I would go 4.10. the formula was new tire size(35) x axle ratio(3.54) divided by old tire size (33)

 

[Bounty__Hunter]

Louisianajeepin, I recommend 4.88 gears. 4.56 would account for the added tire height but not the added mass, therefore its usually best to gear a little bit lower than what the above calculation recommends. In addition, 3.73 to 4.56 really isn't enough of a change to make it worthwhile.

 

[littlesdrag]

69jeepcj thanks. I have the 304ci, also I jacked up the back and counted up one tire revolution to u joint. I came up with 3.73's. Im getting it put back together and I'll just run it and see how she does. It has 30" tires on it now and I have a set of 33" waiting. Thanks

 

[rock316]

if you want a give Bill a call at Tucson Differential (520)-750-1309 he will tell you exactly what you need i worked with him at the shop back in Tucson ,AZ

 

[Sahara707]

My mechanic who's built 150+ Hemi jeeps installed 4.88's in my 2000 TJ. 35" B.F. Goodrich M/T KM2. Check out the gallery at www.jeepspeedshop.com

 

[69jeepcj]

I ran 33,s with the 304, t150 trans several times (just wasn't forking up the dough for gear change) with 3.54 gears and never really had a problem. On the road it was fine, off road it lack some gearing. Over all, unless I really wanted lower gears I wouldn,t pay for a gear change with 33,s and a v8. I have had a jeep with 35 and 3.54 gears and that absolutely sucked.... The 3.73 gears with 35,s and your v8 may be ok on the road but will probably lack some gear offroad, like you said drive it first and see how it does.. A gear change will be less stressfull on your clutch, drivetrain and put your engine in it,s proper powerband. I didnt change mine just because it wasnt worth the expense to me. ooops sorry, I thought your were going to put 35,s on it. I really think 3.73 will pull 33,s with a v8 pretty good.

 

[69jeepcj]

Louisianajeepin, I recommend 4.88 gears. 4.56 would account for the added tire height but not the added mass, therefore its usually best to gear a little bit lower than what the above calculation recommends. In addition, 3.73 to 4.56 really isn't enough of a change to make it worthwhile.

3.73 to a 4.56 is a pretty good jump. Do you mean 3.73 to 4.10 isn,t that much of a change? I would agree! Big expense for a small change.

 

[69jeepcj]

If you go 4.88 gears with a v8 and no overdrive and want to drive on the highway, you will be hating life, I garentee it!! It will be great offroad but forget the highway unless you keep it under 55. I had a overdrive with 4.88,s and the OD went out, now im hating my 4.88,s. The motor is screamin on the highways.