LJ Automatic gear question

[johnsonbz]

Long time lurker, first time poster.

I have a 2004 LJ that I absolutely love. even better than my original 97 TJ. Been mine for about 8 months. I am running 35's on a RE 5.5+1" Body lift.



As I get used to driving it, the 4 speed (42RLE) transmission is driving me nuts. Even with 4.56 (ARBs) It does nothing but lug on the freeway. Parleys canyon is a joke, in order to maintain speed going up the canyon, I have to bury the skinny pedal and then it just wants to jump down to 2nd and spin the tach through the roof. As a brick parachute traveling down the freeway,anything above 60 requires me to push way too hard on the gas. After some internet calculator work I came up with the following chart:

42rle - ___OD=.69 __34.5" tires

__________4.56 ____5.13 ____5.38
60mph __1839 ___2068 ___2169
65 ______1992 ___2241 ___2350
70 ______2145 ___2413 ___2531
75 ______2298 ___2589 ___2712 RPM

Seems about right to me. SO, here is my question. As a daily driver, my brain wont even consider the 5.38s as they are too high and I already spent money on gears...but the math shows very different. Does anyone out there have an LJ or even a TJ with this actual trans/tire combo that is running 5.38 that can give me a positive nod to the 5.38s?

I have an option to buy a front and rear dana 44 with ARB and 5.38s for a great price, but I am wondering if I should just spend that money on trying to tinker with intake and exhaust to boost HP instead.

I am appealing to all years of experience out there to point me in a good direction.

 

[BCGPER]

I ran 4.88's my LJ and loved it. 5.38 would be low, but if you can't live with it, you have enough lift for 37's.

My expierence on the 4.0 intake and exhaust mods netted me zero HP or fuel mileage gains. Od course, your mileage may vary.

 

[johnsonbz]

Good point on the 37s.

Why do so many people insist that intake and exhaust really "wake up" the 4.0? Saw similar zero gain on my TJ Well, it did gain in noise, so I can't say zero gain....


On the RPM side, on freeway I am kicking out of over drive and cruising around 3k anyway, so 5.38s may get me a net decrease (2712) in RPM over all.

 

[Xiled1]

I've got 5.13's &37's on my LJ and its still a bit of a dog. Plus I've got the 6sp. I regularly cruise at 3k or more. 5.38's will really wake it up around town but may limit top end on the highway. If u are willing to live with a top speed of 70 or 75 then they could work. Conventional wisdom says 5.13 is best for 35's but 5.38 is only 5% higher.

Lookin at your chart, you'll be fine at 2712. I'm a little higher than that in 6th and would not mind more. Keep in mind it will still downshift on hills and need upwards of 3500 to keep speed on decent sized hills.

 

[johnsonbz]

I can live with the down shifting as long it does not have to dip into second.... 2712 RPM seems reasonable to me. I spent most of my freeway time north of 3K anyway not in overdrive. I figure if I am loaded with the Fam+Gear, the lower the better. I read that certain people that are "done" with their LJ build, wish they would have used lighter armor all around as it doesn't take much to make the LJ a heavy beast. Hopefully lower gears would help that. Any concern on the size of the pinion?

Being that what I am looking at are D44s, I cant stop thinking about this - http://www.pirate4x4.com/forum/axle...new-sckool-jk44s-your-old-school-housing.html

If I buy the axles already setup, I am looking at $2500 for 5.38+ARB CroMo TJ Rubi axles X2. I think that is a decent price, what do you think? And I can still sell my originals to offset the price.
OR I can spend some cash on just a front G2 or ProRock44, and re-gear my stock rear 44 with the JANA K4. I know the current thing to do is spend the $$ once on 60s or a 14, but it really seems overkill for an occasional Moab trip of my daily driver. And I don't see how I can go bigger than D44 without new wheels, wider axles, and custom mount work......I may be missing something on this....but it seems the minimum I would need to spend to get 5.38s under my LJ is close to $3,000 Any thoughts out there? Is that money better spent elsewhere?

 

[gijohn40]

someone once told me that for an auto with 33 you should go with 4.88 and for a manual go with 4.56 and that is what I did...
I have the 6 spd and 33 inch tires on my LJ with 4.56 gears and I am doing 3200 rpm at 75 mph.... and love the around town...

 

[XJEEPER]

You already know your rig is geared too tall, hence the poor performance and crappy mileage. Gearing a rig is always a compromise between gas mileage and performance. Gearing charts and calculators provided by vendors are great for calculating "stock equivalent" gear ratios, but have no way of factoring in the parasitic drag created by:

1-added rolling resistance/weigh of larger than stock tires/wheels
2- added weight of aftermarket bumpers, winches, armor, cages, trail gear, larger spare tire, etc.
3- increased drag coefficient (think wind friction) by lifting your rig above stock height
4-roof racks- see 3
5-weight of cargo, passengers, etc.
6-elevation/change in which the vehicle regularly operates (high elevation= less oxygen= less HP/TQ produced by engine)
7-typical driving (% of freeway vs town)


These are the reasons why folks who select gearing based on a chart or calculator are nearly always disappointed in the results. While I don't own an LJ, I have owned three 4.0 equipped XJ's over the past 18 years, with various tire/wheel/tranny and gearing combinations. I learned this lesson the hard way on re-gearing my 2nd XJ, the first time.

Lower is better (numerically higher).

The 4.0 I-6 can cruise all day long on the freeway at 2500-3000rpms (70-75 mph) and be perfectly happy. In fact, you will net better fuel economy in this range if your axle gearing allows the trans to stay in OD most of the time, than it will to have a flat ground cruising rpm of 2200-2500 rpms and your tranny is constantly jumping out of OD into 3rd and sometimes 2nd, just to maintain freeways speeds on hills and overpasses.

With my current rig, a 2000 XJ with 4.0 /AW4 (.75 OD) trans/231 t-case, 6" lift, 285/75/16 tires (33 x 11.50), this calculator http://www.currieenterprises.com/cestore/calculators.aspx indicates that with stock gearing of 3:55 and a stock tire height of 27.8", the correct ratio to regear is 4:21.

This ratio is not available for a D30/D44 combo, so one might say, meeeehhh.....4:10 is close enough and I don't want to "over-rev" my engine by jumping up to the next available ratio of 4:56.

Factoring in the 1-7 variables listed above, I ignored the charts and went with 4:88 gears and couldn't be more pleased. Even though my engine has 183,000 miles on it, I still average 16-17 mpg on the freeway at 75mph and 14 around town. I have plenty of low-end power and for reference; I can drive over the Point of the Mountain in either direction with the cruise control set on 75mph and the trans stays in OD. At 75mph, my engine is turning 2800 rpms.
Sorry if this seems long-winded, but hopefully this thread helps others as well who are considering gear ratio changes.

If I was in your shoes, I wouldn't hesitate in jumping to 5:38’s. You'll need to stroke the motor or add a blower/turbo to boost the HP/TQ enough to off-set your current gearing, at which point your fuel economy will likely decrease as well. LS motor swap would solve your power issue, but likely double the cost of the 2 axle deal you've mentioned. Hope this helps.

 

[mbryson]

....and I'll dissent. I had 4.88s and 35" MTRs in my old XJ. Hated it and wished I'd went to 4.56 instead. (That's an AW4 in an XJ. not sure how it compares to the LJ trans OD ratio)

 

[XJEEPER]

You're such a dissenter........AW4 OD ratio is .75, 42rle OD ratio is .69

I ran 4:56 gearing in my 89 XJ with a 5 speed and 33's and it was great, until I swapped out the 5 speed for an AW4. With the auto, the tranny would jump between 3rd and OD at the slightest elevation change on the freeway (every overpass). My fuel economy dropped off as well. After swapping in the auto, I regeared to 4:88's, which corrected this issue. I've been very happy with 4:88's in my 2000 XJ for the past 4 years......YMMV.

 

[DAA]

Yeah. You're a dissenter! Plus, if you hated the 4.88's you would have hated the 4.56's too .

Running 4.88's w/6 speed and 35's on my <heavy> LJ. Spins a solid 3K or a bit over at 75 MPH, while getting 12 MPG. Still can't get out of it's own way off the line, still have to downshift on any real grade. But it's the motor I hate, not the gears .

If I had the 42RLE, which turns an already gutless pig into a wimpering whiney pathetic dog that wishes it could aspire to being a gutless pig, 5.38's would be a no-brainer for me, no decision to even be made. That's just me though.

- DAA

 

[Xiled1]

I've got the Jana 44 kit in my axles. The gears are definitley stronger. But the pinion seals leak. He is still working out that issue. So if u go that route
Make sure you have an experienced gear installer do the work. It takes about double the time of a normal regear if its the installers first time. Plus there will be some trouble shooting with the pinion seals.

 

[mbryson]

Yeah. You're a dissenter! Plus, if you hated the 4.88's you would have hated the 4.56's too .


Running 4.88's w/6 speed and 35's on my <heavy> LJ. Spins a solid 3K or a bit over at 75 MPH, while getting 12 MPG. Still can't get out of it's own way off the line, still have to downshift on any real grade. But it's the motor I hate, not the gears .

If I had the 42RLE, which turns an already gutless pig into a wimpering whiney pathetic dog that wishes it could aspire to being a gutless pig, 5.38's would be a no-brainer for me, no decision to even be made. That's just me though.

- DAA

With that particular rig, I went from 30-31" tires with 3.55 gears, 32, 33 and 35" tires with 4.10 gears and ended with 35" tires and 4.88 gears. I was quite happy with the gearing/power of the 32-33 tires and 4.10 gears. The 35" tires needed more gear and I justified the 4.88 by rolling mass resistance and a tired motor. I went from about 14-16 mpg with 33" tires to about 12 mpg with the 4.88 and 35" tires. Had TONS of pull, though.

 

[glockman]

I'm running 4.88 with 35's in my new LJ. The OD on this transmission is ridiculous. There is a mile between 3rd and OD. That said, running 75 I am just about 2100-2200 RPMs. I would go 5.13's if I was going to regear. 4.88 are live able now for me.


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