Looking for Someone with a JLU, 6 Speed, 35's, and 4.88 or 4.56 Gears

DanW

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I'm going to re-gear my Jeep. I went up very slightly in tire size from 34.6" diameter KO2's to 34.9" Grabber X3's. The slight increase in diameter and higher rolling resistance of the mud tread hit the tipping point for me with 6th gear. On the KO2's, I'd shift into 6th at 60mph and it was ok. Now I feel like 65 is the shift point and it will hold it, but it just bugs me. 1st through 5th is fine, really. And finally, reverse was and is just too tall, with either tire.

So, I've done the math and see the rpm differences. On paper, I very slightly favor 4.88's. But after driving around knowing what the RPM's would be at different speeds, it pushed me back to 4.56, which would give me slightly more rpm than the original stock 33's and the current 4.10 gearing gives. The short time I ran the 33's, 6th was perfectly fine and the engine could pull hills pretty well in that gear.

So the final phase of the decision is at hand. I need to hear from Jeep drivers with manual transmissions, 35" tires, and either 4.56 or 4.88's to see how you like them after living with them. I know it is very subjective, so I'm probably looking more for someone who says something like 4.56 turned out not to be enough, or 4.88's went too far. I have a feeling that either is actually fine in the real world and that both groups will be very happy.

@chevymitchell , whose advise I highly respect, said 4.88's were perfect with 37's. One thing I know for sure is that I won't be going to 37's on this Jeep. There are too many reasons to go into here, but getting 4.88's to keep that option open is just not part of the consideration. If hell froze over or aliens landed at the White House, and I did change my mind, I think 4.56's could pull 37's ok and would leave me no worse off than I am right now, which is liveable. I'm doing this just to fine tune the Jeep, not because it is a dog or not fun to drive. I'd be fine leaving it alone. I just want to make it a little better.

Final thought: Low range is no issue. It is fine now and a final drive change to either choice won't make a huge difference there, for me. Either would only improve on what is already good.

My two areas of concern are 6th, which I've already explained, and 1st. I don't want first to be too short. The difference right now, according to the caclulation, is that redline currently occurs at about 30 right now and would drop to about 25 or 26 with 4.88's, and 28 or so with 4.56.

So help a Jeep brother out and let me know your experiences and thoughts with your re-geared Jeeps! I'd be in your debt for the feedback and help in making the decision. If I don't hear from anyone, I'll make the decision tomorrow and I'm pretty sure I'll be happy either way.
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DanW

DanW

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Ok, I only spoke to one guy on the Gladiator side who had 4.88's with 35's. He loves it, but he's got an auto, so I think it is a little bit apples to oranges.

I went ahead today and ordered 4.56 Dana/Spicer rings and pinions from Northridge and will order the Master Overhaul Kits on Tuesday. I have read of quite a number of folks with the 4.56's but am surprised nobody chimed in here. Maybe not as many people do this, or maybe it is 99% automatics.

I'm guessing I'll get the installation done within the next 4 to 6 weeks, depending on when my friend can get to it.

Thanks @chevymitchell for the advice, and others, too, who have posted info on gear swaps and their experiences throughout the forum.

I'd still love to hear from you if you've done this! I'm pretty excited about it. The Jeep drives pretty well now, but I think this will put it right into the sweet spot for this machine. The help with 6th gear will be the biggest benefit and it will turn 5th into more of a power overdrive that can get up some long highway hills a little better. It will also perform better in the mountains on the way to great trails.

I'll post up when I get it done and will give a thorough review.
 

word302

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Honestly I’m running 5.13s with the manual and 37s and I can’t imagine being higher. I would’ve gone at least 4.88 with your setup but I’m in the northwest and nothing here is flat. I ran the stock 4.10s for a little over a year and it was pretty painful. First is a little short but I can pull hills in 6th again. 4.56 just wouldn’t be worth the cost and trouble for me.
 

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Dan- I can’t help you with your gearing-up questions as I still have the stock Rubicon gears, but before I got even halfway done reading your post I was shocked to see you in 6th gear in the 60’s. I don’t even think about 6th gear till 70 mph, and that’s with the stock 33” KO2’s. If I had 34’s or 35’s I would definitely still be in 5th at <70 mph.

have you considered staying in 5th gear longer?!
 
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DanW

DanW

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Dan- I can’t help you with your gearing-up questions as I still have the stock Rubicon gears, but before I got even halfway done reading your post I was shocked to see you in 6th gear in the 60’s. I don’t even think about 6th gear till 70 mph, and that’s with the stock 33” KO2’s. If I had 34’s or 35’s I would definitely still be in 5th at <70 mph.

have you considered staying in 5th gear longer?!
Yeah, I actually drove much of the way home from Moab in 5th. But it is pretty flat here, so on flat ground, it really doesn't struggle to hold speed in 6th even at 60 with the 315 KO2's. But now it has to be at least 65. Any hills, though, and it is no dice.

I ran 6th gear all the way to Oshkosh 2 years ago at 65mph and got 21.5mpg which is just amazing with 35's. So it does perform ok with the 4.10's at that speed in 6th, but again, that trip was flat as a pancake. It did ok through the mountains to/from Moab, but I was only in 6th going downhill.
 
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DanW

DanW

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Honestly I’m running 5.13s with the manual and 37s and I can’t imagine being higher. I would’ve gone at least 4.88 with your setup but I’m in the northwest and nothing here is flat. I ran the stock 4.10s for a little over a year and it was pretty painful. First is a little short but I can pull hills in 6th again. 4.56 just wouldn’t be worth the cost and trouble for me.
I think if we had more hills or mountains, I'd go with 4.88.

I'd love to hear more about yours with the 5.13's. How many RPM's are you pulling in 6th at 75mph? 75 is my most common highway speed, so it is kindof my benchmark. I'll be at about 2400 in 6th at 75. With 4.88's I'd be at about 2525 or maybe 2550, which isn't terrible. A little buzzy, but still ok. I just really worry about that short 1st gear. I get on it in 1st and 2nd a lot and I feel like when on it I'll be shifting at 23 or 24 with 4.88's instead of the 29 or 30 where I shift now. It moves out pretty smartly as is. I've never really wanted for more power in 1st to 3rd gears.
 
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word302

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I think if we had more hills or mountains, I'd go with 4.88.

I'd love to hear more about yours with the 5.13's. How many RPM's are you pulling in 6th at 75mph? 75 is my most common highway speed, so it is kindof my benchmark. I'll be at about 2400 in 6th at 75. With 4.88's I'd be at about 2525 or maybe 2550, which isn't terrible. A little buzzy, but still ok. I just really worry about that short 1st gear. I get on it in 1st and 2nd a lot and I feel like when on it I'll be shifting at 23 or 24 with 4.88's instead of the 29 or 30 where I shift now. It moves out pretty smartly as is. I've never really wanted for more power in 1st to 3rd gears.
I’ll have to pay more attention next time I drive. I’m out of town for the next few weeks but I’ll try and remember to get back to you. When I’m on it I feel like I’m shifting to 2nd pretty close to 30 but again, I haven’t paid that much attention.
 

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I posted this in another thread... hope this helps...

Finally got the gears done this week, I am very happy! 4.56 with the 3.6L manual on 35's is a perfect fit for me. I think if I would have gone to 4.88 I would have hated it. I do a fair bit of freeway driving, and so far so good. I haven't taken her off road yet, as I am still breaking in the new gears. I have to say, being able to use 6th gear again is awesome!

1st gear is quick, if I'm on a bit of a down hill grade at a stop, I use 2nd to pull out. As for freeway driving, I haven't gone above 65mph yet, but so far no down shifting for wind or a 1% grade.

This was an upgrade for 3.45s. I think if I would have had 4.10s I would have saved the money and not upgraded.

I'll do another update once I have a long road trip, and a bit of off road action with them. First impression is solid.

4.56 + 3.6L + 6 Speed Manual = My Approval.
 
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DanW

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I posted this in another thread... hope this helps...

Finally got the gears done this week, I am very happy! 4.56 with the 3.6L manual on 35's is a perfect fit for me. I think if I would have gone to 4.88 I would have hated it. I do a fair bit of freeway driving, and so far so good. I haven't taken her off road yet, as I am still breaking in the new gears. I have to say, being able to use 6th gear again is awesome!

1st gear is quick, if I'm on a bit of a down hill grade at a stop, I use 2nd to pull out. As for freeway driving, I haven't gone above 65mph yet, but so far no down shifting for wind or a 1% grade.

This was an upgrade for 3.45s. I think if I would have had 4.10s I would have saved the money and not upgraded.

I'll do another update once I have a long road trip, and a bit of off road action with them. First impression is solid.

4.56 + 3.6L + 6 Speed Manual = My Approval.
I'm with you, it's just right. I've had 4.56 gears now for about 1400 miles and a couple months.

You'll only find more goodness above 65mph. That engine gets to a place in the power band where it will pull right up hills and through whatever headwind you might encounter. It is soooo much better than the 4.10's. I can't imagine how much better it must feel than with the 3.45's.

The more I drive it, the more I love it. I've got a big overlanding trip to VT, NH, and ME coming up in a few weeks. It'll man-handle the Jeep loaded down with gear. Going to Moab last spring, I ran 5th gear at 75mph most of the way, once we got out of the flat lands and when there was a head wind. That's now a thing of the past. I went wheeling with the 4.56 gears off road a couple weeks ago in Kentucky and the crawl ratio is just insane. It has to be around 90:1 in first gear and 4 low.
 

Shantz

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You'll only find more goodness above 65mph. That engine gets to a place in the power band where it will pull right up hills and through whatever headwind you might encounter. It is soooo much better than the 4.10's. I can't imagine how much better it must feel than with the 3.45's.

I went wheeling with the 4.56 gears off road a couple weeks ago in Kentucky and the crawl ratio is just insane. It has to be around 90:1 in first gear and 4 low.
Good to hear, I'm looking forward to the first road trip. With the 3.45s I was always running in fourth on the freeway.

Offroad is what I'm looking forward to the most. It would struggle on a tough climb, even in 4 low.

Thanx for the feed back.
 
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DanW

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Good to hear, I'm looking forward to the first road trip. With the 3.45s I was always running in fourth on the freeway.

Offroad is what I'm looking forward to the most. It would struggle on a tough climb, even in 4 low.

Thanx for the feed back.
I'm betting even with the Sport T-case's taller ratio, you'll have an excellent crawl ratio that will power you up any climb you want!
 

Shantz

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I'm betting even with the Sport T-case's taller ratio, you'll have an excellent crawl ratio that will power you up any climb you want!
I think I worked it out to now be around 63:1... should make a massive difference!
 
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DanW

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I think I worked it out to now be around 63:1... should make a massive difference!
That's pretty darned good. What's the math formula to calculate that? I'm guestimating mine to be around 90:1. I think factory with 33's and 4.10 gears and 1st gear's ratio made it 84:1. The XR with 35's, manual and 4.88 gears is 100:1.

I think tire diameter of the General Grabber X3 tires I've got right now is 34.6". The KO2's on the XR lands at about 34.4.
 

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That's pretty darned good. What's the math formula to calculate that? I'm guestimating mine to be around 90:1. I think factory with 33's and 4.10 gears and 1st gear's ratio made it 84:1. The XR with 35's, manual and 4.88 gears is 100:1.

I think tire diameter of the General Grabber X3 tires I've got right now is 34.6". The KO2's on the XR lands at about 34.4.
First gear x tcase low range x axle ratio = crawl ratio.
 
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