JLUR Manual trans: 3rd gear feel underpowered?

[Toycrusher]

The thing with a manual transmission, is that you are in charge of gear selection. Regearing from 4.10 to 5.13 makes a big difference in first gear, torque is greatly multiplied for much faster acceleration. However, once you grab second, there's not much difference, and beyond that, there are no real-world gains.

The 3.6 pulls decent from 3000 rpm up. I have 37s on stock gears. On the highway going 80 I use 4th gear at about 3200 rpm. The engine doesn't have enough torque to hold 80 in 5th at 2500 rpm.
If I regeared to 5.13, 80 mph would fall at a similar 3200 rpm but in 5th gear. The effective ratio of motor torque-to ground speed is about the same. The same power required to accomplish the same amount of work. At virtually any speed from 25 mph up, I have access to the same amount of engine power with the stock gears by using a lower gear in the transmission.

The only advantage of regearing is in applied power below 25 mph. For street driving, considering how hard it is to make a fast 1-2 shift with the ridiculous rev hang when trying to shift near redline, I don't see any advantage in regearing. Mine drives like any other 5-speed.

On steep hill climbs when off-road, there have been times I wished I was geared a bit lower, but even then, the bigger issue is low end torque. Dropping to 5.13s in 4Lo only gives me an extra 500 rpm to work with when climbing a steep grade at 5 mph, not a night-and-day improvement

Things are different in an automatic equipped vehicle, particularly old 4-speeds. My Ram on 38s with the old 46RE transmission was a dog until I swapped to 4.56 gears. But with modern 8+ speed transmissions, there's relatively little to be gained with deeper axle gears

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[Kluk Ztopolovky]

Hambone don't forget the this Pentastar 3.6 likes to run in little higher RPM. It takes time to get used to it. It drives differently than your typical VW or Fiat stick . This motor has enough of torque and so it seems to drive OK doing 30 - 35 even in the 4th gear and you could do it even in the 5th but do not be afraid to run the engine little higher .I often shift to the 5th gear and then realize I should really be in 4th so I can get more response from the Jeep when I need to accelerate a bit. I truly enjoy driving again because I can kind of play with the gears and modify my driving technique according to the mood I happen to be in. If Dire Straits is on I will push the 3rd and if it is mellow notes of Chopin I can easily float in the 4th or even 5th gear.

 

[sf5211]

I felt it a little weak at 3rd gear as well but this was when the Jeep was new. Now with the engine broken in and experience with this trans. Much better.

 

[8flat]

The thing with a manual transmission, is that you are in charge of gear selection. Regearing from 4.10 to 5.13 makes a big difference in first gear, torque is greatly multiplied for much faster acceleration. However, once you grab second, there's not much difference, and beyond that, there are no real-world gains.

The 3.6 pulls decent from 3000 rpm up. I have 37s on stock gears. On the highway going 80 I use 4th gear at about 3200 rpm. The engine doesn't have enough torque to hold 80 in 5th at 2500 rpm.
If I regeared to 5.13, 80 mph would fall at a similar 3200 rpm but in 5th gear. The effective ratio of motor torque-to ground speed is about the same. The same power required to accomplish the same amount of work. At virtually any speed from 25 mph up, I have access to the same amount of engine power with the stock gears by using a lower gear in the transmission.

The only advantage of regearing is in applied power below 25 mph. For street driving, considering how hard it is to make a fast 1-2 shift with the ridiculous rev hang when trying to shift near redline, I don't see any advantage in regearing. Mine drives like any other 5-speed.

On steep hill climbs when off-road, there have been times I wished I was geared a bit lower, but even then, the bigger issue is low end torque. Dropping to 5.13s in 4Lo only gives me an extra 500 rpm to work with when climbing a steep grade at 5 mph, not a night-and-day improvement

Things are different in an automatic equipped vehicle, particularly old 4-speeds. My Ram on 38s with the old 46RE transmission was a dog until I swapped to 4.56 gears. But with modern 8+ speed transmissions, there's relatively little to be gained with deeper axle gears

One factor that you're forgetting is that gearing down the diffs gives the advantage of each transmission gear effectively gives you a shorter "range", so that would be an advantage at all speeds.

Like an old physics professor told me, to make a problem's solution a little more clear, take the options to extremes. In this case, if you geared up beyond the factory 4:10s all the way to 2:10, you'd basically be left with, what, 2 gears usable? Acceleration in both first and second would really suffer. On the flip side, if you geared down to 5.88s (or lower) and had a usable 6th at highway speeds, each gear would have a shorter useful range and your engine would be able to accelerate your jeep quite a bit better, at all speeds.

This is why 8 and now 10speed autos are getting popular. Engines benefit from more gears with short spreads.

 

[geem03]

Sweet spot for third gear is 35mph to 50mph. Don’t shift into 3rd under 35. Should notice a more responsive feel. These engines love the higher rev limit.

True dat!

 

[Dogboyslim]

Anyone with a bike knows that more gears are better. The less power the engine, the more important the gear options. I put 34s on my jeep and then geared it at 5.13. I chose the 5.13s because they put my 75 mph interstate RPMs at 2500. That way it keeps the speed on hills. Stock wheels had me running just over 2k rpms at 75 and any hill would make me slow down because there is no torque under 2k RPM. I'm happy with it now. My mpg runs 15/16 with this setup at 75. At 55 I get 18-20.

 

[Toycrusher]

One factor that you're forgetting is that gearing down the diffs gives the advantage of each transmission gear effectively gives you a shorter "range", so that would be an advantage at all speeds.

Like an old physics professor told me, to make a problem's solution a little more clear, take the options to extremes. In this case, if you geared up beyond the factory 4:10s all the way to 2:10, you'd basically be left with, what, 2 gears usable? Acceleration in both first and second would really suffer. On the flip side, if you geared down to 5.88s (or lower) and had a usable 6th at highway speeds, each gear would have a shorter useful range and your engine would be able to accelerate your jeep quite a bit better, at all speeds.

This is why 8 and now 10speed autos are getting popular. Engines benefit from more gears with short spreads.

That is true, however, your final drive ratio (transmission gear x t-case gear x axle ratio) for a given speed can be matched pretty closely once you get beyond about 25 mph. Given the real world usage of the average JL, 0 - 80 mph, and the fact that, unless your in a school zone, your speed will be 35+ mph, you gain next to nothing from a gear swap. 1st gear is already incredibly low, before I upgraded to 37s, I would always start out in 2nd because 1st was simply too short. With 37s, 1st gear is appropriate for take-off, and 6th becomes inappropriate for any speed. I'm still using 5 gears (1st-5th) just like I did before upgrading tires (2nd-6th).

I have future plans for hi-line fenders and 40s, hoping to still avoid a lift, but maybe a 2" will be necessary. At that point, running 40s, 1st gear will become too tall and I'll have to regear. But for now, with a manual transmission, stock 4:10 gears are totally appropriate for my 37" tall tires. When off-road, I typically choose 4-Lo instead of 4-High and simply start in 3rd and shift up to 6th instead of running 4-hi and using 1st - 3rd.

 

[Toycrusher]

Anyone with a bike knows that more gears are better. The less power the engine, the more important the gear options. I put 34s on my jeep and then geared it at 5.13. I chose the 5.13s because they put my 75 mph interstate RPMs at 2500. That way it keeps the speed on hills. Stock wheels had me running just over 2k rpms at 75 and any hill would make me slow down because there is no torque under 2k RPM. I'm happy with it now. My mpg runs 15/16 with this setup at 75. At 55 I get 18-20.

Your 21-speed bike analogy is perfect. How do you typically shift through those gears? If your on a hill you may run through the low gears, but typically, you start in Medium-1st, shift up to 7th, then shift to high. You don't go through all 21 gears because Low-5th is the same as Medium-2nd and so on and so forth.

 

[8flat]

That is true, however, your final drive ratio (transmission gear x t-case gear x axle ratio) for a given speed can be matched pretty closely once you get beyond about 25 mph. Given the real world usage of the average JL, 0 - 80 mph, and the fact that, unless your in a school zone, your speed will be 35+ mph, you gain next to nothing from a gear swap. 1st gear is already incredibly low, before I upgraded to 37s, I would always start out in 2nd because 1st was simply too short. With 37s, 1st gear is appropriate for take-off, and 6th becomes inappropriate for any speed. I'm still using 5 gears (1st-5th) just like I did before upgrading tires (2nd-6th).

I have future plans for hi-line fenders and 40s, hoping to still avoid a lift, but maybe a 2" will be necessary. At that point, running 40s, 1st gear will become too tall and I'll have to regear. But for now, with a manual transmission, stock 4:10 gears are totally appropriate for my 37" tall tires. When off-road, I typically choose 4-Lo instead of 4-High and simply start in 3rd and shift up to 6th instead of running 4-hi and using 1st - 3rd.

Egad I sure can't start out in 2nd with factory tires, at least not without slipping the clutch more than I'd like. This engine is just too gutless.
Sounds like this gear works well for you especially in 4-LO, i can sure understand that part, this case is almost geared too low for me to be useful.
But, you'd sure see better acceleration with lower gears, you'd turn your 4 speed back into a 6 and have give the engine a little advantage when it's working hard down the highway or in a headwind.

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