What diff gears for 99 XJ with 4L engine, AT, and 30 vs 31 inch tires? - Page 2 - JeepForum.com
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Go Back JeepForum.com > Models > Jeep Cherokee & Comanche Forums > XJ Cherokee Technical Forum > What diff gears for 99 XJ with 4L engine, AT, and 30 vs 31 inch tires?

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Unread 05-15-2013, 11:26 PM   #16
RockRodHooligan
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Too bad you didn't live closer to me, just found a 99 XJ, 2 door, 2wd, 4cyl, 8.25..... If I am correct that would be a 29 spline 8.25 with 4:10s.... Can pick it up for about $110

I'd pick it up, but I've already decided on doing an 8.8. 31 spline, 1/2" larger ring gear, disc brakes, LSD.... For $40 more.

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Unread 05-16-2013, 12:36 AM   #17
Charley3
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Originally Posted by sAe23 View Post
And you do realize that the words "Cherokee" and "decent gas mileage" don't go together, right?
My 96 XJ got 23 mpg on highway with 235/75R15 with Cooper AT driving 68 mph.

I'd call that "decent" gas mileage for a mid 90s SUV.

A friend of mine with a mid 90s XJ was getting 25 mpg on highway with 225/75R15 P rated highway tires driving 68 mph.

Though we did have a trick up our sleeves. Use a 205F thermostat in a 4L engine (AC Delco makes best 205F) and you get 2 or 3 more mpg. Driving 68 mph helps too.
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Unread 06-04-2013, 07:01 PM   #18
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I want 3.9 gears for my D30 on my 99 XJ.

Does anyone make 3.9 gears for D30 that works with 99 XJ?

I ask because I was told that 3.9 gears might not be available for the rotation direction of a 99 XJ D30.

I've been Googling, but so far haven't found an answer.
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Unread 06-04-2013, 08:43 PM   #19
foggybottombob
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All the gears rotate the same way but high pinion gears are reverse cut. There are no 3.90 gears for a high pinion Dana 30.
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Unread 06-04-2013, 09:54 PM   #20
rugsucka
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You're not going to get 3.90 gears for your heap.

Just get 3.73 for economy or 4.10 for a bit more power.

There is no point in trying to find a rare species of gear when you can find those other two gear sets often for sale already set up in an axle that will bolt in.

You're splitting hairs for something you haven't even completely decided on the tire size. I ran 31's on 3.55 gears for a couple years but never felt I needed to regear. Now I'm at 33's and looking at 35's - that's a much better reason, and if the right set of axles popped up, I wouldn't fret over 4.56 or 4.88. It's all a wash at that point.
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Unread 06-04-2013, 10:04 PM   #21
Charley3
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Arrg! I love spliting hairs, but I'll have to accept reality.

I hate reality! .

Thanks guys for letting me know.
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Unread 06-05-2013, 11:51 AM   #22
foggybottombob
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I have 31s and 3.92s in my XJ. It is perfect. But I have Dana 44 axles on both ends.
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Unread 06-05-2013, 03:56 PM   #23
Charley3
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Quote:
Originally Posted by foggybottombob View Post
I have 31s and 3.92s in my XJ. It is perfect. But I have Dana 44 axles on both ends.
How'd you get D44 front and rear?

What transmission? What size tires?
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Unread 06-05-2013, 03:58 PM   #24
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I have decided to run 3.73 gears because will work really well for 30" tires I have, and will work OK for 31" tires if I go bigger in future. I won't ever want larger than 31" tires.

---

Edited in Later: 3.73 would be ideal for 30s, and OK for 31s, but 4.1 would be better for 31s.

(3.9 reverse cut gear unavailable for high pinion D30)

I like my 30 x 9.5 R15. So I'll have to wait and see if I really want 245/75R16 load C (31 x 9.5 R16), or just stay with 30s.

I won't change gears until I make a permanent decision on tire size.

For now, I'll just drive the 30s with 3.55 gears for 10K miles or more before I decide.
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Unread 06-05-2013, 04:13 PM   #25
Floreancig_XJ
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Sorry to threadjack but my jeep is a 99 4l ax15 8.25 rear , im gonna be putting on 33's in a couple weeks... Don't i have the lowest ratio, and js that bad lol
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Unread 06-05-2013, 04:33 PM   #26
Charley3
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Quote:
Originally Posted by Floreancig_XJ View Post
Sorry to threadjack but my jeep is a 99 4l ax15 8.25 rear , im gonna be putting on 33's in a couple weeks... Don't i have the lowest ratio, and js that bad lol
Hijack all you want. I'm done with this thread because I got the advice I needed. Thanks everyone.

Go ahead and use this thread for your purposes and post about your Jeep and ask questions as much as you want. It's all good.
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Unread 07-01-2013, 05:11 AM   #27
stevemongr
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3.55 and 31 is terrible

3.55 and 31's suck. Worthless in the soft sand and highway driving.
4Lo works good but the highway still sucks. A 40mph headwind or hills will drag it down.
4.10 next week
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Unread 07-01-2013, 11:28 AM   #28
CitadelXJ
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I've got 31" Cooper Discoverer STT's, 3.55 gears, locked front axle, and 6" of lift. The only issue I have with it is my fuel economy. Other than that, I haven't had any issues offroad. The only times I really get stuck is if I high center. And on the street, mine can still smoke some of those turbo Hondas. I mean hell, stock gears, 262k on the motor and I can still do a freakin' burnout on 31" MT's.
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Unread 07-01-2013, 11:34 AM   #29
Millermagic
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We have some pretty big hills in CNY and 31's and 3.55s seems to work relatively well for my cherokee. It does have to shift a bit more than I would care for, but I don't hav ethe $1000 to drop to get a regear.

I don't like how there is a huge gap in the gears available for the 8.25. Ideally I want 4.30 for when I make the switch to 235 85/16 ... but there's only 4.10 and 4.56. When I go bigger, I guess I'll have to go to 4.10.
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Unread 07-02-2013, 03:20 AM   #30
Charley3
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Quote:
Originally Posted by Millermagic View Post
We have some pretty big hills in CNY and 31's and 3.55s seems to work relatively well for my cherokee. It does have to shift a bit more than I would care for, but I don't hav ethe $1000 to drop to get a regear.

I don't like how there is a huge gap in the gears available for the 8.25. Ideally I want 4.30 for when I make the switch to 235 85/16 ... but there's only 4.10 and 4.56. When I go bigger, I guess I'll have to go to 4.10.
Slightly off topic, but I those tires you want are all load E. That will ride very harsh on an XJ.
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