Re-gear and 4.0L 42RLE

86cj

Explorer
My question to all you heavy TJ and LJ Jeeps is:
If I select a ratio like 5:38 or 5:13, will the O/D stay engaged with the throttle input needed to cruise 65MPH when heavily loaded and in windy conditions or on grades other than flat (not steep mountains of course). If I have to shift to 3rd or 1:1 often, the RPM's will really be to high for normal highway speeds (mid 3000's) and slowing to 55-60 (3000RPM) would be a bummer if it something that occurs often on day of big miles.

I run 33's and 3:73 in my heavy LJ and when not in O/D I run about 2700RPM at Hwy speed and can climb most any mountain with traffic and get decent MPG, with a little better power at 3000RPM. I know if I get down below 2200RPM in 3rd it will tend to down shift to 2nd more easily. It seems like 4:88 or 4:56 would be better if I spend alot of time in 3rd, but they bring the RPM's in O/D closer to 2000 rpm at 65MPH and could cause the downshift. My seat of the pants tells me 5:13 or 5:38 could be the sweet spot, IF the transmission can stay in O/D except on the most unusual grades or loads.

This is really a seat of the pants or 42RLE drivability issue as much as a math RPM question. I was thinking you guys who tow are even more loaded than I am and probably have an opinion on this O/D subject.

I like my 33's but can't rule out 35's some time after the re-gear, so if you run 35's don't be afraid throw in your 2 cents.

Thanks again........... the experience here is amazing
 

Jeep

Supporting Sponsor: Overland Explorer Expedition V
I put 4.10's in my TJ with 33's with great results. I think a good gear for the tire size would be 4.56's if you are a little heavier. 5.38 or 5.13 might be a bit low, you will have a very high pinion speed which will have an affect on lifespan as well as a very small amount of gear contact area which will affect strength. I am upgrading to a 60 rear and 44 front and going to 4.88's with 37" rubber.
 

ExpoMike

Well-known member
Fairly common in the Jeep world that 31" tires = 4.10's, 33" tires = 4.56's, if you basically want to keep the stock power band/RPM as stock. If you do a lot of crawling or heavy towing, going up to the next gear ratio can help too.

As for your current setup, 3.73's on 33" tires, you're going to have the downshift to 3rd issue but you can rev it higher and not be a problem. I commonly run about 3300 RPM's (3rd) at just under 65 loaded up with the trailer in tow. It will run all day at that RPM and I only loose about 1-2 mpg doing so.
 

mrchips

Adventurer
My LJ Rubicon geared to 4.88 with 6 spd and 33 tires. Runs great pulling an AT Chaser loaded, and on flat ground 6th gear 55 mph in cruise control no issues rpm at 2500.
Hills I drop down to 5th or 4 th and can make the top.
Be care full going to a 5.13 ratio as now you have no meat on your pinion gear, it is getting smaller, and have heard of them stripping.
Also extremely important who does your gears and sets them up to the exact tolerances
 

86cj

Explorer
Be care full going to a 5.13 ratio as now you have no meat on your pinion gear, it is getting smaller, and have heard of them stripping.
Also extremely important who does your gears and sets them up to the exact tolerances

I might not have these issues, I am currently looking at bolt in Front Axles. I like the "New Generation D44" with the high pinion and stronger internals. The Mopar/ Dynatrac even has much thicker tubes, fixing it's known defect. It is alot of money and I am looking at all options out there.

I have been planning to find a 03-06 Rubi 44 for the front and trussing it or just beefing the brackets and re-gearing it, instead of spending any money on my D30. Front axle strength has been a reason I have not went to 35" tires, so it's likely to happen after the re-gear, which is one of the reasons I mentioned the 5:38 and 5:13's..

I did not wait for the Rubicon to come out when I bought my Unlimited in 2004 because the 4:1 case just does not work for me. I have been planning to upgrade my axles since then...
 

PhulesAU

Explorer
you'll be limited by the low pinion d-30 on the front end to 4.88. that gear ratio and 33's will be great. I'm running it with 35's and it's at the edge, big hills ok OR winds ok Both Well let's say Areodynamics are over rated.
 

mrchips

Adventurer
Even the Rubi D44 are a weak axle, should not run larger than a 33 tire. If you want to go bigger go with a different axle. D44 Rubi tubes and outer knuckles are a all D30, weak.
 

dynamike

Observer
Opinions are like ......well you know.
my 2 cents, go with 5:13's and never look back !!!
I did a WHOLE lot of research on this entire subject, with all the factors involved. My LJ weighs in at 5369 pounds, I know, I know. It needs a diet.
But this is not my weekend warrior vehicle. I use it offroad for my temporary line of work and everything I need, I have with me. The 5:13's are the best mod done to the Jeep. Even my wife said OMG, if I would have known what it would do, that would have been the first mod. I roll down the road at 65 mph in overdrive and turn 2400 RPM, a slight grade or wind has no effect (like it use to shifting back and forth) Off road 4 low was almost to low, it wanted to drive through the brakes. Feels as though I am driving a bobcat (tractor). 4 high was fine. I have since went to a 35 inch tire, and now turn 2200 RPM at 65 in OD.
I am aware of all potential weak points with gearing , axles etc.
I still say it is the best thing I have done. Also, I am not hard on the skinny pedal, (no spinning). most things I can crawl right over, if not, I use an alternative (to spinning the tires). And on the street/highway the 5:13's are perfact. PS. it is the auto tranny 42rle
 
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86cj

Explorer
Yea I know, and Thanks for the opinion, Your rig is a good match for my issue.

It's good to hear you can give some decent amount of throttle input in O/D and the trans won't downshift. The last time we were loaded and on the road, 2000-2200RPM really seemed like a break point for the trans to want to down shift. I am just curious if the 42RLE transmission behaves the same in O/D, (I have not been a fan of it's shift programming). I also have not really used O/D at all, the 33's went on at 36 miles, even an overpass bridge will cause the transmission to shift out of O/D and into 2nd! so we don't use it.

I really don't mind downshifting to 3rd to climb a grade (or 2nd if I am lucky enough to be coming out of Denver). I just don't want to do it on every little grade change or wind gust.

Your set up is pretty much what I am thinking so far, 5:13 w/35's and 4:88 if 35's are not in the future plans.
 

PhulesAU

Explorer
the dana 30 can handle 35's just fine. As with any other "factory" part, if you drive badly it can fail. I'm pushing 114k, about 80 of that has been running it's current gearing and tires. I wheel it fairly hard. I've yet to damage either axle becuase of tire size. I have bent the front, because everyone knows that Jeeps can fly...... They just don't land well.
 

outdoors

Observer
Go 4.88's imho... I liked 4.56's in my last LJ.. Great gear (4.56's)for the D30 front. If you go any deeper you loose tooth contact on the R&P. Although 4.88's seem to be holding up "pretty well" out there using 35's but being sensible. 5.13's or deeper? you really don't need them over the 4.88's imo.. D30 5.13's and a front locker equal breakage! 4.88's and enjoy the best of both worlds.
again I went 4.56's last time only to keep what strength I had in the small but durable D30 R&P.
Why do i say 4.88's today? If you break you can upgrade the axle and still have the gears you prefer.
Enjoy..:smiley_drive:
 

86cj

Explorer
the dana 30 can handle 35's just fine. As with any other "factory" part, if you drive badly it can fail. I'm pushing 114k, about 80 of that has been running it's current gearing and tires. I wheel it fairly hard. I've yet to damage either axle becuase of tire size. I have bent the front, because everyone knows that Jeeps can fly...... They just don't land well.

If the LJ did not spend so much time exploring thousands of miles from home, I would run the Dana 30 until it failed, but we are alone most of the time.

When wheeling the dunes locally, Flying Jeeps are only one brain fart away....


Looks like a "New Generation Dana 44" High Pinion front axle is going in my LJ..........

I just can't decide on a housing, one that accepts common lockers and use my outer knuckles with it's small axleshafts, U-joints, 11" brake rotors.

Or a housing that uses JK knuckles with 3150 U-joint axleshafts and some 12" rotors, but only accepts the factory E-Locker. The JK "C's" will have a gusset and the weak stock axle tubing won't be used.
 

Root Moose

Expedition Leader
I just can't decide on a housing, one that accepts common lockers and use my outer knuckles with it's small axleshafts, U-joints, 11" brake rotors.

Or a housing that uses JK knuckles with 3150 U-joint axleshafts and some 12" rotors, but only accepts the factory E-Locker. The JK "C's" will have a gusset and the weak stock axle tubing won't be used.

That's a hard call.

I like options but by the same token I haven't heard anything untoward about the stock JK locker. My only other option I'd be interesting in pursuing is an ARB so I'm guessing it is a wash in that regard when compared to the JK differential.

I'd probably base the decision on which has the largest brake package available. On the small tube axle you can run WJ brakes if so inclined. I don't know how they compare to the JK stuff though.
 

RedRocker

Adventurer
Most folks on the Rubicon board say 5.13's with 33's and for sure with 35's.
4.88's with 33's is the route I'm going, I have no desire to go to 35's.
 

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