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Old 03-04-2014, 04:14 PM   #1
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42RLE/35's/D30 Question

Ok gang, I have an 04 TJ with the 42RLE, D44 rear, and D30 front with 3.73s. I am going to go with 35's. According the the gear charts ideal gear ratio is 4.56 but with the 0.69 OD gear I was going to bump it up to 4.88. After searching the forums it seems that with that combo 5.13's are the best choice. But the D30 only allows up to 4.88. So my question is if I stick with my D30 and go with the 4.88's how much difference will I see compared to the 5.13's? I am going to upgrade axles and install the Detroit Trutracs. I do not really do rock crawling, I mostly do mud, snow, fields, and creek beds. Maybe once or twice a year I go to off road parks in Indiana, nothing too extreme. It is not a DD so the only time I commute in it is if it is snowing too much to get the car out. Advice/opinions from anyone with a similar setup would be appreciated!

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Old 03-04-2014, 04:51 PM   #2
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Sorry to say you need to settle for 33in tires and 4.88's or upgrade your front axle to run 5.13 or 5.38 (actually better). That's the price you have to pay to run 35's with the 42RLE and its crazy overdrive.

I'm currently running 31's with the 4.0L / 42RLE and 4.56's. There are many days I wish went with 4.88's as I still find myself turning the overdrive off. Yes, that's wasn't a typo....31 inch tires.

I don't know what the manufacturer was thinking when they put that transmission in a 4000lb vehicle that's as aerodynamic as a billboard. I'm sure it's a great transmission for a car or minivan but definitely not a Jeep!

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Old 03-04-2014, 05:05 PM   #3
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4.88s with 35s and 42rle suck. OD stays off until I reach highway speed. The slightest incline caused the transmission to constantly downshift.
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Old 03-04-2014, 06:24 PM   #4
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Sorry to say you need to settle for 33in tires and 4.88's or upgrade your front axle to run 5.13 or 5.38 (actually better). That's the price you have to pay to run 35's with the 42RLE and its crazy overdrive.

I'm currently running 31's with the 4.0L / 42RLE and 4.56's. There are many days I wish went with 4.88's as I still find myself turning the overdrive off. Yes, that's wasn't a typo....31 inch tires.

I don't know what the manufacturer was thinking when they put that transmission in a 4000lb vehicle that's as aerodynamic as a billboard. I'm sure it's a great transmission for a car or minivan but definitely not a Jeep!
Right on point. Swap the front axle or stick with 33s. I stuck with 33s and 4.88s. It'll work fine for what you're doing.
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Old 03-04-2014, 06:25 PM   #5
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Originally Posted by fadec View Post
I'm currently running 31's with the 4.0L / 42RLE and 4.56's. There are many days I wish went with 4.88's as I still find myself turning the overdrive off. Yes, that's wasn't a typo....31 inch tires.
That's quite a bit lower ratio than the stock setup, even lower than the rubicon factory setup. I believe that you're not happy with it, but then you wouldn't be happy with any stock Jeep combo available.

Mathematically speaking, the 42rle with 4.88 and 33" tires is a perfectly acceptable (probably just perfect) combination. I wouldn't want to go any deeper for 33's on that transmission but I definitely would for 35's which would make the front axle useless.

I run 31's with the 42rle and 3.73 gearing, I need OD for 65 mph and up bit that's it. I usually run with it off until I hit 60, where with the OD on I'm seeing 2k rpm.
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Old 03-04-2014, 06:36 PM   #6
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So what's the most economical upgrade for the front axle if I went that route? The Dana 44's are a little expensive. Is the HP30 the best option?
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Old 03-04-2014, 06:43 PM   #7
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So what's the most economical upgrade for the front axle if I went that route? The Dana 44's are a little expensive. Is the HP30 the best option?
again, the deepest you can go with a D30 is 4.88s. that puts you at 33" tires.

your options are basically a D44, hybrid 9", D60, etc if you want bigger tires. or suffer with the power loss.
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Old 03-04-2014, 06:53 PM   #8
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I will mention that in reading your stated uses I see no reason to justify the expense of even considering 35" tires. 33's would likely be more than enough tire for your stated use and will save you at least a few thousand dollars.
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Old 03-05-2014, 01:27 AM   #9
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I agree my current uses would only need 33's. But I figure if I build it to be capable to have even more fun then I will probably take it on trails more often. I've had buddies that built their's with the normal 4 inch lift and 33's then took them out and wished they had went 35's. I have no intention of getting rid of the jeep so I thought I would just avoid re-building in 5 years to increase everything again.
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Old 03-05-2014, 06:37 AM   #10
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I have a D30/D44, 42rle, 4.88s, and 35's.
It's not ideal, but not as bad as everyone would have you believe.
It's certainly a hell of a lot better than 3.73's and 33's were.
I'm still looking for a front axle replacement. Going on 3 years.
The Jeep has been having fun all over the mountains of the PNW in the meantime.
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Old 03-05-2014, 07:59 AM   #11
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I have a Rubicon with 35s and the stock 4.10 gears in it. It definitely doesn't have the same power as stock , but I find it acceptable. I never use the OD and I live at 8700 ft and drive it exclusively in the mountains . I don 't use it for a daily driver. Of course most of my outings are rock crawling trails at high elevation, as opposed to mud. If I ever break a diff I'll regear , but I don't find it bad enough to be worth the expense.
I think you'll be fine with 4.88s.
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Old 03-05-2014, 08:10 AM   #12
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I never use the OD
this means you've gone from a 4 speed to a 3 speed transmission, you've lost an entire gear.

and what's interesting for the mountains is you've really lost the gear on the lower end too. you now can't go as slow as you could with a properly geared setup...whether thats holding the Jeep back on a street downhill or off-road downhill. Because you have a 4:1 t-case, you can compensate for that off-road pretty well....but if you had a 2.7:1 t-case like the OP, you'd be quite surprised on the steep downhills...you'd have to ride the brakes a bunch.

The 6-speed manual is much more forgiving on gearing, and the 42RLE really brings out the deficiencies.

For reference, if you do the RPM/gearing math, you'll see a 42RLE/3.73s/30s turns the same RPMs as a 6-speed/3.73s/35s...minus 1st and 3rd gears.
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Old 03-05-2014, 08:28 AM   #13
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yeah, I don't think anybody'd be happy with 3.73s and 35's, but 4.88s are getting reasonably close. When I first responded I thought he had 4.88's and was thinking about changing axles to get higher gearing than that, so I did a quick edit to my reply.
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Old 03-05-2014, 09:35 AM   #14
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I'm running 35's, 4.88, and the 42RLE & I'm seriously consider finally doing my own regearing to get to 5.13, or 5.38 if that ratio is now somehow doable for my Rubicon axles. I can't afford to pay someone else to do the job any more but I hate my present 4.88 gearing enough that I'm thinking it's time to regear to a lower ratio on my own.

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