Originally Posted by silverbullet88

For those that have re-geared and for those that have not.

3.8/Auto/35's or 37's/ 4.10s. Or with 5.13s etc.

What are your opinions on this? Realistically with overdrive off your turning 2900~ or so rpms. And with a re gear it's 2500~ or so. Both in the power band.

So no matter what the transmission is still going to downshift when going up a hill right?

Besides losing 4th gear all the time with o/d off what else am I missing? Do the 5.13's actually help stay in 4th on hills? Generate more torque per say?

Originally Posted by Trail Jeeps

The thing with the 42RLE is that it has tall gears and internally is about as big around as a loaf of bread. It is barely up to the task of moving a stock JK around, let alone of portly, lifted JK on big tires. Combined with the anemic 3.8 you need all the help you can get gearing wise all the way around. Because of those tall gears in the transmission, you can basically step up one ratio in comparison to traditional thinking for gears to get the same performance. You are also reducing strain on the transmission every time you step to a lower gear set. The 3.8 loves RPMs, and being wound up on the highway doesn't seem to effect fuel economy all that much, fuel economy out of this engine basically sucks across the board. Because they guzzle raw fuel to cool themselves, they are SUPER sensitive to load and heat. When gearing a 3.8, you can basically go as low as you want without many of the traditional consequences of going too low with something like a 4.0 L6, other than noise and *technically* additional wear and tear because the engine is physically moving more. If you have a loud exhaust it can get very obnoxious quickly though, 3.8s have a tendency to drone and don't lend themselves to a pleasant exhaust note. It's kinda like a Subaru making a loud fart, FOREVER, if you have a long drive... I'll put 3.8/auto customers on 5.13s with 35s without batting an eye from a technical standpoint, if you see a lot of flat highway 4.88s work well, too. With a 37 a 5.13 is a go to choice. 5.38s are good performance wise, but start to because pretty fragile. It is worth nothing that if you wheel your Jeep hard, you will have to make the choice between performance and strength, as the pinion gear starts to get pretty small with those low gears, especially in the front. If you're whomping your Jeep, you might stop at a 4.88 gear for a D30, and a 5.13 for a D44. 5.38s aren't even available for a D30 front, and should be driven gingerly on a D44 set up.

Originally Posted by silverbullet88

If I were to regear to 5.13's that would put me around 2350-2500 or something. That would barley be efficient to move me along and it would most definitely downshift to 3rd which would now put my third gear much closer to 5k. So if I were to keep O/d off like I do now I would be out of my sweet spot.

Does that make sense?

Originally Posted by silverbullet88

Iv found that leaving overdrive off is the best option for me. 65-70mph I am around 2750-3000 rpms. I can hold that rpm and speed OK for some hills until it downshifts to 2nd reaching around 4K rpms and I finish off the hill. Overall I'm happy cruising along in 3rd. Perhaps something is wrong with my motor? I still lose speed at 3k rpms until it downshifts.

If I were to regear to 5.13's that would put me around 2350-2500 or something. That would barley be efficient to move me along and it would most definitely downshift to 3rd which would now put my third gear much closer to 5k. So if I were to keep O/d off like I do now I would be out of my sweet spot.

Does that make sense?

Originally Posted by Trail Jeeps

I mean, yeah I guess that makes sense, but this is one of those times when I can say "you're not doing it right." There is nothing wrong with your motor, it's a 3.8. It could suffer from low compression because it's been flogged within an inch of its life while on the highway, so you might want to get that checked. I think it might be time to change some expectations. Peak horsepower for a 3.8 is at somewhere around 5000 rpm but that doesn't mean you want your engine to live there. You have multiple gears, you definitely want to use them. What you're doing is hard on your engine and transmission and killing the overall performance. Sure, it's doable but far from ideal. You want to cruise at an RPM that requires the least amount of throttle input while holding speed through various conditions with your transmission in overdrive until you encounter a hill or want to pass. Simply railing on it is not really the way to go, it might get you there but is going to drink a lot of fuel and be harder on the vehicle. Outside of wear and tear, you are going to have a lot of throttle to cruise around, which is burning more fuel. I suppose I'll refer back to this: Quote Originally Posted by Mike H. View Post go to this website Gear Ratio Calculator in 1 column enter 4.10's, in the other enter 5.13's and compare the 2 side by side. I used 42RLE for transmission, NVG241or for t-case and 33.75" tire for 35's. With 5.13's, in 3rd gear, 60mph you're going to be sitting at ~3050rpms, 70mph will be at ~3600rpms. With 4.10's, in 3rd gear, 60mph you're going to be sitting at ~2450rpms, 70mph will be at ~2850rpms. You say it is dropping into 2nd gear now... sooo... With 4.10's, in 2rd gear, 60mph you're going to be sitting at ~3850rpms, 70mph will be at ~4500rpms. Since under load the 3.8 is going to work best between 3500-4500rpm (TQ peak)... I'm betting that you will go up moderate/typical grades in 3rd at 70mph with 5.13's(3600rpm) that currently with with 4.10's will be asking for 2nd gear to do 60mph(3850rpms). I'm also betting it will go up lots of slight grades in 4th at 2400rpm where currently it's looking for 3rd and 2850rpms. Good luck. This is a very good post and is correct. 2400rpm is still kinda high for freeway cruising compared to a lot of other engine/trans set ups, but the 3.8 does fine. I also found this for you to look at: https://www.jk-forum.com/forums/modi...m-3-8l-337250/ You might also have a look at this: 42RLE Poor Performance - Applies to ALL 4 speed owners - LOOK HERE! [Archive] - Lx Forums | Dodge Charger Challenger Magnum | Hellcat | SRT | Chrysler 300 Forum about how the slushy 42RLE functions, you might be experiencing some of this. I've been there, it's frustrating. In the end, it's up to you. If you are happy with your set up, who am I to come in and tell you you're wrong? I can tell you that if you regeared to something like a 5.13 it would feel like you dropped a second engine in there, with faster acceleration and a transmission that functions as the factory intended. You can do a regear and throw a programmer on there for a little 20 hp (so they claim) bump and have a much more functional set up.

Originally Posted by nthinuf

I get where you're coming from, just looking at your numbers. Dropping to 3rd with 5.13's would put you around 3500. Where did you get 5000? 5.13's and 35's (with a measured height of 34") 2450 rpm @ 70 (divide by .69 for OD/Off) 3550 rpm @70 And as someone else posted from the gear calculator, with 4.10's, you are 2850 rpm @ 70 OD/Off. And then dropping to 2nd and sitting at 4500 rpm @ 70. So: 5.13's 4th = 2450, 3rd = 3550 4.10's 3rd = 2850, 2nd = 4500

Originally Posted by silverbullet88

I should probably have it checked. While accelerating I hear what sounds like a rattle or marbles and it is not a crack in the header. Ideas? Honestly it feels like a good rpm around 2850 while 2400 range feels luggish when I hit the gas pedal. I understand the wear and tear aspect on the transmission. With 5.13's it would be easier on it to get up to speed/ shift ect. My tires only measure around 33.25

Originally Posted by silverbullet88

I should probably have it checked. While accelerating I hear what sounds like a rattle or marbles and it is not a crack in the header. Ideas? Honestly it feels like a good rpm around 2850 while 2400 range feels luggish when I hit the gas pedal.

I understand the wear and tear aspect on the transmission. With 5.13's it would be easier on it to get up to speed/ shift ect.

My tires only measure around 33.25

Originally Posted by Trail Jeeps

Sounds like raspy marbles? You sure it's just not the sound of the 3.8? Ok all joking aside, it's impossible to diagnose a sound over text, but what you're describing sounds like pinging, AKA detonation or pre ignition. It isn't good for the engine. There could be a few culprits for it, but I'd have it checked out and figure out what's going. Time to take it to a shop and get a health check. The rattle could be something as simple as a heat shield, so don't freak out. The 3.8 is a turd of a motor in these things, and this might just be a matter of expectations. Gears will make your life infinitely better, but in the mean time I would go get these noises checked out.