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So, I lifted my jeep and put 31x50 mud tires on it and I get 11 mpg, I want to get new gears but I have know idea which ones to get. I have a renix 4.0 with the Aw4 automatic tranny with the 30/35 axles. I live in a somewhat hilly area and do some highway driving but I want good offroad power also. So I really want to know what gears I should get.

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Are you taking into account the tire size difference in your milage calculations? If you havent changed your speedo gear to reflect your taller tire size, your milage calculations are going to be off one way or another. It may not be as bad as it seems.

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Well my front axle doesn't disengage(miss spelled?) because of the vaccum thing so that is part of why I get 11 mpg. I got 13 before I lifted it due to the axle.

 

 

The axle disconnect shouldn't have anything to do with it.

 

There is something wrong and gears won't fix it,with the same set up as you and stock gears with a non disconnect axle my XJ was getting around 18mpg and had plenty of power.

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I have two experiences with a (Renix era) 4.0 litre automatic with stock 3.55 gears on 31" tires. Can't recall the city mileage, but remember getting 21mpg cruising at 75mph. Both those experiences were with axles that didn't disengage (Selec-trac Cherokee, and a Comman-Trac with the disco delete).

 

That was better than the 19mpg my stock tires got at that speed, although at 60mph my stock tires got 24mpg which the 31x10.50s couldn't catch.

 

When was the last time the O2 sensor was replaced?

 

As for gear ratio, 3.73 is probably closest to stock, 4.10 for some added torque.

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the front axle doesn't affect mileage. if it did, ALL 4wd vehicles today would have a disconnect. yet they don't.

 

you need to change the speedo gear so that your speedo is accurate with the taller tires. :thumbsup: it's easy and cheap.

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  • 3 weeks later...

Does the 14 mpg take your speedometer and odometer being off because of the larger tires into account?

 

Okay, now back to the regear:

 

3.73 will put you back more or less to the stock final drive ratio and get the speedometer and odometer to read correctly or close to it. That is what I would go with. The transfer case has a 1:2.72 low range for off road, which is plenty. If you do insist on having more torque available at the wheels I would go with 4.10 gears, but your mileage will get worse again.

 

BUT I would not waste the money on regearing the rear Dana 35. Count on $400 to $500 per axle to regear them. You should be able to get a 29 spline Chrysler 8.25" out of a 97 or newer Cherokee for $100 to $150. If you have patience you can get it with the correct gears you want already installed. If staying spring under axle, pay $10 or so for a pair of stock spring perches and about $20 to have them welded on in the correct place. A few minutes with a cutting disk on an angle grinder will take care of the Cherokee perches and shock mounts, and a grinding wheel on the same will get the area where the welding needs to be done nice and shiny.

 

Even a front axle you might be able to find with the gears you want for less than the cost of a regear. Stay away from Grand Cherokee and 2000/2001 Cherokees as they are low pinion, Believe TJ ones are as well. If you get one from a 97 (96? 95?) or newer Cherokee it should already have shafts with the larger/stronger u joints and no axle disconnect.

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Well my front axle doesn't disengage(miss spelled?) because of the vaccum thing so that is part of why I get 11 mpg. I got 13 before I lifted it due to the axle.

 

That vacuum disconnect wouldn't affect your mileage by 1% of that much. The factory eliminated the disco in 91 or so. They wouldn't have done it if the EPA numbers were gonna go down.

 

You still haven't adderessed the fact that if you haven't calibrated your speedo to account for the taller tires.

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the front axle doesn't affect mileage. if it did, ALL 4wd vehicles today would have a disconnect. yet they don't.

 

you need to change the speedo gear so that your speedo is accurate with the taller tires. :thumbsup: it's easy and cheap.

 

 

Any idea where to get the speeding gears now? The dealer by me said the long gear that we need is no longer orderable. I've been looking for one for a while.

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the front axle doesn't affect mileage. if it did, ALL 4wd vehicles today would have a disconnect. yet they don't.

 

you need to change the speedo gear so that your speedo is accurate with the taller tires. :thumbsup: it's easy and cheap.

 

 

Any idea where to get the speeding gears now? The dealer by me said the long gear that we need is no longer orderable. I've been looking for one for a while.

 

the tooth count for your set up is listed in the DIY section. here's a recent forum where people were successful in purchasing the gears

 

viewtopic.php?f=2&t=34605

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Does the 14 mpg take your speedometer and odometer being off because of the larger tires into account?

 

Okay, now back to the regear:

 

3.73 will put you back more or less to the stock final drive ratio and get the speedometer and odometer to read correctly or close to it. That is what I would go with. The transfer case has a 1:2.72 low range for off road, which is plenty. If you do insist on having more torque available at the wheels I would go with 4.10 gears, but your mileage will get worse again.

 

BUT I would not waste the money on regearing the rear Dana 35. Count on $400 to $500 per axle to regear them. You should be able to get a 29 spline Chrysler 8.25" out of a 97 or newer Cherokee for $100 to $150. If you have patience you can get it with the correct gears you want already installed. If staying spring under axle, pay $10 or so for a pair of stock spring perches and about $20 to have them welded on in the correct place. A few minutes with a cutting disk on an angle grinder will take care of the Cherokee perches and shock mounts, and a grinding wheel on the same will get the area where the welding needs to be done nice and shiny.

 

Even a front axle you might be able to find with the gears you want for less than the cost of a regear. Stay away from Grand Cherokee and 2000/2001 Cherokees as they are low pinion, Believe TJ ones are as well. If you get one from a 97 (96? 95?) or newer Cherokee it should already have shafts with the larger/stronger u joints and no axle disconnect.

 

I also would not waste the cash on regearing the 35 UNLESS you get the Super 35 kit with the c-clip eliminators. I have 2 buddy's with super 35s running 35 inch tires and they have never broke their Super 35.

 

For a front axle, I wouldnt be scared to get one from a 00-01 if you cross paths with one. The LP is just a tiny bit weaker (from what i've read) then a HP. You are not really looking for strength hear, just a solution. I'm thinking you would be hard pressed to find a front 30 geared 3.73. I do believe ZJs with a towing package got those gears.

 

That being said, I drove over 40k miles in my DD XJ on 3.55s and got around 17 IIRC.

 

My MJ project, axles have 3.55s. Going to see how I like it and how it tows my boat, but I will probably end up going to 4.10s. Its only 500 bucks to swap gears if you have good mechanics in your Jeep Club!!

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Its only 500 bucks to swap gears if you have good mechanics in your Jeep Club!!

 

 

$#!& try free. if your in a good club and know the people, offer to provide food and drinks for lunch. jeep guys like wrenching anyway, the food/drinks just draws more poeple in willing to help. :thumbsup:

 

we have "lift parties" and "gear install parties" all the time down here. its great being in a club. plus you get discounts from 4wp and 4wd and probably other places in the like

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