Is my LJ Rubicon supposed to feel gutless?

psdtime

psdtime

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Feb 19, 2019
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I have a 2005 Jeep Rubicon LJ Auto that I bought last August. I really wanted that body style/size and I had to get an auto so that anyone (wife, sisters) could drive it when we went camping. I really like it, but it seems really gutless and inefficient at highway speeds. I just hoping to find out from you all if that is just the nature of the beast, or maybe there is something wrong with the motor. I have 285/75/16 tires (33") on stock wheels with a 4" long arm kit. It is a bit heavier than I was hoping at 4500lbs (have a scale at work) which I attribute to the winch and Hanson bumpers front and rear. The Jeep does fine off the line, but it has a hard time holding overdrive unless the road is perfectly flat. It gets around 10-11 mpgs in mixed driving. I live on the coast in California, so we are talking about 0-500 feet elevation. Do you think what I am experiencing is normal?
Thanks in advance
 
You probably have stock 4.10 differential gears. For 33's, you'd want 5.13's. For 35's, you'd want 5.38's. The 42RLE automatic transmission you have has a very very tall overdrive ratio which is leading to the problems you describe. Regearing will make a world of difference.
 
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Gears man , gears. Engine is fine , it's a 4.0. Find @Rob5589's shop or another good one and get it regeared.
 
It needs to be re-geared, ideally to 5.13. Those 4.10 gears are in no way whatsoever ideal for 33" tires with that 42RLE transmission.

However, after owning a number of 4.0s, I can tell you that a faster highway speeds (especially going up hills) they are anemic. They don't flow very well up high, and after having talked to a number of 4.0 engine builders, they have said this is in large part due to the design of the head, and the super restrictive stock header.
 
A temporarily solution is turn off the O/D whenever you start it up and it'll feel a bit more powerful, but it'll still struggle with acceleration and hills until a regear, which would return it to more stock characteristics (which as Chris mentioned isn't a race car but is much more livable)

I wouldn't rule out 5.38 for 33's also, but do your own research.
 
Thanks for the help folks, I was hoping that wasn't the case since gearing seems to be really expensive. I didn't think that going up like 2" in tire size would necessitate new gears, but if the engine is on the weaker side, I guess it does. I priced it out a few months ago and was told $2400 to re-gear from one shop and $2400 an axle from another shop. Obviously one costs twice as much as the other, and I wouldn't go that route, but does $2400 seem appropriate? I'm 4 hours from Sacramento (Monterey) so the person suggested above is probably too far for me to travel.
Thanks again.
 
psdtime said:
Thanks for the help folks, I was hoping that wasn't the case since gearing seems to be really expensive. I didn't think that going up like 2" in tire size would necessitate new gears, but if the engine is on the weaker side, I guess it does. I priced it out a few months ago and was told $2400 to re-gear from one shop and $2400 an axle from another shop. Obviously one costs twice as much as the other, and I wouldn't go that route, but does $2400 seem appropriate? I'm 4 hours from Sacramento (Monterey) so the person suggested above is probably too far for me to travel.
Thanks again.
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Your LJ was under-geared from the factory. For 31" stock tires, Jeep should have put in 4.56 or 4.88 gears instead of the 4.10's they did. The 42RLE has an overdrive ratio of 0.69, which is pretty tall compared to the top gear ratio of the manuals.

$2400 is ridiculous. Total to re-gear should be around $1500 for both axles. That number does depend on your region, but I couldn't imagine that it would be $2400 (especially per axle!). If I was in your position, I would probably put 5.38 Revolution gears in. If you ever decide to go to 35's, 5.38 would be what you want. 5.38 with 33's wouldn't be terrible either.
 
My Rubicon had 4:10 and 33's and wouldn't get out of its own way...I regeared it and it's fantastic.
 
It’s a shame really, but what everyone has said here is correct. Part of the expense in owning a 42rle is knowing you need to regear it (even stock!) it’s a big expense but super worth it after you feel the improvement and power! The 4.0 is a beast of an engine and will rock withoff with the right setup!
 
A regear should be less money than you posted if I'm thinking right, Rob will know the market .
 
Regear it to start with. Even after regearing with 35s it's still not going to perform great. On our cross country road trip I could tell any time the Jeep got over 2k feet in elevation and I would start complaining any time we got over 4k. At sea level it was okay. Even on flat roads at those elevations, you can not only tell that your engine isn't breathing but also the acceleration is poor compared to other vehicles on the street around you. At 9kft you're lucky to be going half the speed limit. Forced induction is the next step.
 
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The 4.0 is so weak but only when forced to pull bigger heavier tires, bigger axles, r&p's, and any number of heavy mods added to the Jeep. The 190 horsepower 💩 4.0 is best suited for the stock setup, anything other than that and IMO, its time to look at something with close to double the Hp and Tq.
 
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I run 33s in a TJR with the 6speed and 4.10s. It works great. Towing a trailer i'm often in 5th, but on a long straight I wish for 3.73s in 6th. The issue with the automatic is the outrageous 0.69OD. No matter what ratio you pick, the jump from 3rd to 4th will be huuge.
 
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billiebob said:
I run 33s in a TJR with the 6speed and 4.10s. It works great. Towing a trailer i'm often in 5th, but on a long straight I wish for 3.73s in 6th. The issue with the automatic is the outrageous 0.69OD. No matter what ratio you pick, the jump from 3rd to 4th will be huuge.
Click to expand...
I'm a fan of that overdrive ratio, but it would be better suited for something with more horepower. I believe the 4L60E, 4L80E, and the R4 all have .70 overdrives and no issues, but they have power producing V8's in front of them.
 
yeah, my Tundra had a 0.54 double overdrive with a 5.7L V8.... An Audi A8 hits 150mph in 5th gear and loses speed in 6th, 7th and 8th. Triple overdrive. Overdrive is meant to lower rpms, emissions and improve gas mileage. Direct and gears lower are built for performance. Gear for the performance you want down one gear in a TJ..... unless you have the automatic when you might need to compromise.
 
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