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Discussion Starter #1
I did searches and I saw that a guy with a CJ was told to go for 4:10s because it was also a DD, as opposed to 4:56s. Does the same apply to an XJ? I also found and bookmarked that XJ History link. That is a really good link!
 

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Kinda depends on, tire size, engine, tranny, axles, driving style, possible tire size in the future, etc. If you have over drive I would go deeper than you originally thought
 

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Discussion Starter #3
Stock 6 cyl. inline engine, stock 4 speed automatic AW4 tranny is what build sheet says, moderate to tough trail riding. Nothing really extreme. We had 4:10s put in it already. We will eventually upgrade to maybe D44s, and 35 or 36 inch tires. We have 33s on now. And we do have overdrive. Is there anything else you need to know, or did I cover it all? I'm a noob and I do appreciate your patience with me. I saw what happens to some, like that metal works guy. WOW! Funny though.:D
 

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If you upgrade to 36's and D44 front and rear, I would opt for 5.13's. If you stick to 35's I would do 4.88's. The 4.0L like the revs at highway speeds, you get better gas mileage.

The rule of thumb for a 4.0L with auto in a XJ is:

31-32 - 4.10's
33-35 - 4.56's
35-36 - 4.88's
35-37 - 5.13's

The last two really depend upon where in the country you live and what type of wheeling you do.
 

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Discussion Starter #5
Thanks for the rules of thumb with tire size and gears. I did forget to put in my post that the engine is a high output, but y'all probably already had that figured in. I bookmarked this page also for future referance.
 

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I also found and bookmarked that XJ History link. That is a really good link!
Your welcome!

Anyway, with an auto you dont need to gear as low as you would with a manual (the torque converter slips and makes up for it). What kind of wheeling do you do?

That rule of thumb that was posted is great for rockcrawling/and mild wheeling, but might be a little to low of gearing for fire roads/light wheeling/camping adventure type stuff. But since you mentioned 35's-36's I think the given ratios would work perfefct for you. And don't forget to swap your speedo gear in the t-case when you change gears so your speedometer won't be off.
 

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Does the same apply to an XJ?

For future reference gear ratio has nothing to do with body style. What gear ratio depends on (things already mentioned) tire diamter, trans, intended use, and what RPM you want at a given MPH. Those are the factors determing what gear you want.(and trail use)

If you want 2000 RPM's @ 70 MPH.....you can't run 5.86's with a 31" tire.

If you want to turn 44's without your rig being a PIG, you can't run 3.08's.


I used extreme examples there so it would be easier to get what I was saying. So, it depends on what you want to use it for. From the sounds of your intended use, I would slap in 4.56's for 35-36" if you thnk sligtly more street than trail, and 4.88's if you think slightly more trail than street
 

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Discussion Starter #9
George wants to tackle this, it's called Rock Creek In Rausch Creek Offroad Park in PA. It is about 1800 feet long and 50 feet wide, but it's a killer! Some of you might recognize the XJ on the rocks, it's ralphxj. I used his pic as a referance to show the size of the rocks.


 

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What terrain?

Are you looking to improve on or off road performance? Like the guys above said, it really depends on the wheeling type. Changing diff gears is most effective at changing street manners. It of course changes off road, too, but not very quickly. For lower off road gears, transmission and transfercase gears are where you want to make the changes. How is it handling on the road with the 33s and 4.10's? If it has plenty of pep, a change may not be necessary. You can run 36's on 4.10 and higher easily if you are not too worried about being able to burn out at street lights or maintaining full speed on highway hills. When you get into super low gears like 4.88 and lower, the pinion is getting smaller and smaller, increasing the chance of breaking that instead of drivelines. Not to say they are weak...they are still pretty dang hard to break, but 3.54-4.10 have more surface contact.
Again - all user preference. If you need the extra power off road for crawling with 36's, get a 4:1 kit for the t-case. If it is too slow on the street as it is, gear down the diffs. If you can live without the extra power on the highway, 4.10 would probably do. With the extra weight of the axles and such, 4.56 would probably be a good middle ground, and 4.88-5.13 would keep the power available on the hills and allow your overdrive to be kicked on longer.
I am running 33's on 3.54 and a manual transmission and it works fine...a little wimpy on the hills in 5th gear.:D
 

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I run 4.56s with 35s and have no issues.80 mph on the hwy @ 2200 rpm, crawls along nicely on the rocks, 19-20 mpg on the highway.
 

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Discussion Starter #15
I run 4.56s with 35s and have no issues.80 mph on the hwy @ 2200 rpm, crawls along nicely on the rocks, 19-20 mpg on the highway.
Wow, our gas mileage is like half of that! But we have some other issues that are affecting that right now, too. I think we will prolly go with the 4.56's eventually. Thanks for the input everybody!
 

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Wow, our gas mileage is like half of that! But we have some other issues that are affecting that right now, too. I think we will prolly go with the 4.56's eventually. Thanks for the input everybody!

Good choice.
 
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