July 1, 2011
Changing 3.55 gears to 4.56 gears in my 1998 Jeep Cherokee?
I own a 1998 Jeep Cherokee Sport 2wd/4wd. It has an automatic transmission. The gas mileage is terrible and I’ve read on the internet that by changing the gears would make a noticeable difference in the fuel economy of the vehicle. I was wondering how much money I would have to spend on the new 4.56 gears, what is the best kit or product to buy, how long it might take to install myself, and if anyone has done this before?
Also if anyone has any other cheaper fuel saving methods other then not driving, it would be appreciated.
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Filed under Gas Conservation FAQ by on Jul 1st, 2011. Comment. 
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Comments on Changing 3.55 gears to 4.56 gears in my 1998 Jeep Cherokee?
changing to a higher-number gear is actually going to make your mileage worse. if you want better mileage you need to drop down to a 3.33 or a 2.70
I believe that the cut off for carriers is 3.73. If you want to put 4.56s on, you will need to replace the gear carrier as well. I think that 3.55 is the tallest you can fit inside your carrier. As for replacing gears, it is NOT cheap. The gears and bearings/seals are not that expensive, having them installed will be. This not something you can do in your driveway. The ring and pinion must mesh properly. The only way to do it will be to have it calibrated on a machine. That is where you pay lots of money. Replacing gears is not an easy or cheap undertaking. You will need to replace gears in both axles.
The reality of your situation is the fact that no matter what you do to that 4.0L engine, you will not see an appreciable gain in MPG. About the only thing you can do to improve it will be to get an intake manifold from a 99-04 4.0 jeep, any model. Get a K&N FIPK for it too. With these mods, you will get a small boost in MPG and a bit more power too. One note, get the intake manifold either from someone who is parting out their jeep or a junkyard. Dont go to the dealer because you will get ripped off royally. Another way to gain MPG is to look into converting it over to HHO. Just do a check online for HHO and you will see what I mean. I am in the process of doing that to my jeep as I write this.
What size tires do you have? With stock roughly 28″ tires and 3.55 gears you should be right about 2769 RPM at 60mph in a 1:1 drive gear with the same tires and the 4.56 gears you’ll go to 3557 RPM at 60 mph.
It’ll cost about $600 in parts and 6 -7 hours if you know what you’re doing and have all the tools. I’m doing the same thing to my 94XJ but the gear change is needed due to 33″ tires.
Changing gears will only help if you have over sized tires. See this article for more gas saving tips for your Cherokee.
http://mikestrawbridge.com/XJMPG.shtml
Mike
http://mikestrawbridge.com/jeep-cherokee-off-road.shtml
Well I think changing the gears should help to some extent in saving fuel , but that again depends if you are going to use the vehicle for long drives on freeways or short city travel.
I think you should opt in for a real good fuel saver kit that can boost your jeep performance.
To startup with you can surf a couple of sites that offer similar products , like this one I came across recently :
http://www.savefuelmilage.com
Hope it helps u ..