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Old 05-17-2017, 07:25 PM
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Stumped for regear opportunity...

Hey guys, I need your advice!

Recently picked up a JKU auto with 3.21s and am planning to get a rear selectable locker installed. This is my DD and just want the extra traction insurance when dealing with deep snow (until it gets too deep of course)

I don't plan to go any larger than the stock 32" tires.

Previous JK was a manual regeared to 4.10 with an e-locker and it was almost perfect from the drivetrain perspective (RPM was just a tad too high on the highways for my liking). I figure that if i'm gonna get a locker in this new Jeep, i'll take the opportunity get some 3.73s since it's an auto.

To my shock, a new set of 3.73 gears is prohibitively expensive!, Like twice the price of more "hard core" ratios especially for the front D30.. so I had to do some thinking.

I was able to score a front D30 set of used 3.73 gears with the open carrier and the spider gears still in them (whoo!) but then I read on various forums that "used gears should never be installed in another housing" So i'm back to square 1. I'm starting to give up on the regear idea...

So should i just suck it up and stick to the 3.21s?

This would at least free up the budget for a nicer rear locker like an ARB. Or with the driving I do (a lot of snow) maybe Truetracs front and rear would be better...

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Old 05-17-2017, 07:35 PM   #2
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You can install used gears just look for a set that came out early in life. My buddies shop has a ton of OEM 3.21, 3.73, and 4 10 laying around. Maybe a shop by you does as well.
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Old 05-17-2017, 07:41 PM
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You can install used gears just look for a set that came out early in life. My buddies shop has a ton of OEM 3.21, 3.73, and 4 10 laying around. Maybe a shop by you does as well.
I called the shop I went to last time, they weren't put off by the idea of installing someone else's take-offs, just that they rarely if ever have any 3.73s come by since everyone's regearing from 3.21s. Not sure how old these gears are, but to my untrained eye, they look pretty good?. I guess I could have the shop take a look at them but they're kind of a long drive away.
D44 3.73s on the other hand are reasonable $ and I don't mind buying new.
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Old 05-17-2017, 07:51 PM   #4
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4.10 with 32 inch tires. The JK 3.6 is happier at higher RPMs.
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Old 05-17-2017, 08:00 PM
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This is the used D30 gears I got. Not sure if anyone here could tell if they're young and worthwhile installing or not.







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Old 05-18-2017, 07:29 AM
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I guess if it fails, this'll give me an excuse to get a truetrac up front along with the new front gear. Assuming there is no collateral damage.
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Old 05-18-2017, 10:21 AM   #7
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Is the 3.6 really happier at higher rpms? Like with 4.10s and 32s, if you were cruising at around 58 miles per hour, would you be in 5th instead of 6th so you could be near that 2500 rpm spot? We have a lot of 55 mph speed limits on the state highways here. Some of them get to 65 when you get out into the rural areas. Have you ever drove or sat in a 5 speed auto JK and watched the tach?

Also, OP has the 5 speed auto. 3.73s in top gear is very close to 4.10s with the manual.

Let me retract that statement... 4.10s on the manual in 6th gear is like inbetween 3.73 and 4.10s with the auto.
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Old 05-18-2017, 01:14 PM   #8
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This is the used D30 gears I got. Not sure if anyone here could tell if they're young and worthwhile installing or not.








Those look almost new i would run them. Installing gears is not that difficult but you will want to go slow the first time and try several different pinion depths when checking your pattern just to get an idea how far it moves when you add or subtract shims.

All you really need is a cheap $30 dial indicator from harbor freight, $25 Vernier Caliper or micrometer. $80 beam type inch pound torque wrench and a cheap $150 harbor freight shop press. and a big soft dead blow hammer. You can modify other stuff to work like a heavy piece of angle iron to hold the yoke with when torquing the pinion nuts.
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Old 05-18-2017, 01:19 PM   #9
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I've got an essentially stock driveline, other than larger tires. Went from stock to 33x12.5", and have been trying to read through all the posts/threads about what is needed to be done to regear/install selectable lockers...so thanks, this seems like a good thread.
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Old 05-19-2017, 06:11 AM
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I've got an essentially stock driveline, other than larger tires. Went from stock to 33x12.5", and have been trying to read through all the posts/threads about what is needed to be done to regear/install selectable lockers...so thanks, this seems like a good thread.
With 33s, I think 4.10 would be perfect for you
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Old 05-19-2017, 08:42 AM   #11
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Originally Posted by efm-7 View Post
With 33s, I think 4.10 would be perfect for you
I think that was the conclusion I came to reading through another thread.

At this point, I did contact my local ORV shop for a possible cost/quote of a regearing / potential selectable lockers, but haven't heard anything back.

If I could, I'd really like to do the work myself (I like tinkering), but seeing as this is a daily driver, and I drive a LOT (like over 100 per day), that's a little difficult.

However, day dreaming about the process for removing the stock gear set and installing a better fit set does make the day at the office go by so much quicker...
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Old 05-19-2017, 09:13 AM   #12
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Is the 3.6 really happier at higher rpms? Like with 4.10s and 32s, if you were cruising at around 58 miles per hour, would you be in 5th instead of 6th so you could be near that 2500 rpm spot? We have a lot of 55 mph speed limits on the state highways here. Some of them get to 65 when you get out into the rural areas. Have you ever drove or sat in a 5 speed auto JK and watched the tach?

Also, OP has the 5 speed auto. 3.73s in top gear is very close to 4.10s with the manual.

Let me retract that statement... 4.10s on the manual in 6th gear is like inbetween 3.73 and 4.10s with the auto.
The OP has automatic. 4.10 on an auto with stock tires. I have a Rubicon auto 2014. I had 4.10 gearing stock. I have 5.13 now with 37s. Yes I have watched the tachometer. Again, the JK engine is at optimal performance at the higher RPMs. I do 2700-2800 at 70, so just a little deeper than stock, and can cruise all day long.
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Old 05-19-2017, 09:15 AM
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Now I'm dealing with the possibility of having to get the rear carrier drilled out for the factory 1/2" ring gear bolts... the confusion and difficult decisions never end! lol
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Old 05-19-2017, 09:31 AM
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The OP has automatic. 4.10 on an auto with stock tires. I have a Rubicon auto 2014. I had 4.10 gearing stock. I have 5.13 now with 37s. Yes I have watched the tachometer. Again, the JK engine is at optimal performance at the higher RPMs. I do 2700-2800 at 70, so just a little deeper than stock, and can cruise all day long.
And 5th gear on the auto is nearly identical to 6th on the manual. And I was indeed fairly happy with 4.10 on my previous jeep which was manual. *that* regear was mostly for driving enjoyment. But my priorities have shifted and would like to balance a bit more highway fuel economy into the decision, especially now that I'm driving a heavier jeep. but maybe there won't be a difference.
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Old 05-19-2017, 12:29 PM   #15
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There have been people who installed shorter gears to match their larger tire size and their fuel mileage improved (compared to what they were getting with the larger tires and taller gears). Fuel mileage is not just a case of taller gears equal better fuel mileage. If the gearing is too tall and the engine is operating outside of its "happy place", fuel mileage may suffer.
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Old 05-19-2017, 12:49 PM
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There have been people who installed shorter gears to match their larger tire size and their fuel mileage improved (compared to what they were getting with the larger tires and taller gears). Fuel mileage is not just a case of taller gears equal better fuel mileage. If the gearing is too tall and the engine is operating outside of its "happy place", fuel mileage may suffer.

This is why I want to regear - engine really feels like it's under too much load with the 3.21s. But my "gut instinct" tells me that 4.10 is overshooting it a bit.
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Old 05-19-2017, 12:56 PM   #17
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Hey guys, I need your advice!

Recently picked up a JKU auto with 3.21s and am planning to get a rear selectable locker installed. This is my DD and just want the extra traction insurance when dealing with deep snow (until it gets too deep of course)

I don't plan to go any larger than the stock 32" tires.

Previous JK was a manual regeared to 4.10 with an e-locker and it was almost perfect from the drivetrain perspective (RPM was just a tad too high on the highways for my liking). I figure that if i'm gonna get a locker in this new Jeep, i'll take the opportunity get some 3.73s since it's an auto.

To my shock, a new set of 3.73 gears is prohibitively expensive!, Like twice the price of more "hard core" ratios especially for the front D30.. so I had to do some thinking.

I was able to score a front D30 set of used 3.73 gears with the open carrier and the spider gears still in them (whoo!) but then I read on various forums that "used gears should never be installed in another housing" So i'm back to square 1. I'm starting to give up on the regear idea...

So should i just suck it up and stick to the 3.21s?

This would at least free up the budget for a nicer rear locker like an ARB. Or with the driving I do (a lot of snow) maybe Truetracs front and rear would be better...

Should you keep your 3.21 gears? I hated mine with my manual transmission and 32" tires - especially when towing my camping trailer in the mountains. The 3.73's made a world of improvement, and I can still get 21 mpg on road trips. I would never go back to 3.21's.

I had my set of USED 3.73 gears installed in my housings about 10,000 miles ago -- no problems at all so far. The rear came with LSD so I scored there. The shop (which specialized in Wrangler suspension and gearing work) only charged me $850 for the gears and install, including new gear oil front and rear, and friction modifier for the rear LSD. I couldn't be happier. Do some research to find shops near you, and talk with them to see what you can learn and find.
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Old 05-19-2017, 01:09 PM   #18
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Now I'm dealing with the possibility of having to get the rear carrier drilled out for the factory 1/2" ring gear bolts... the confusion and difficult decisions never end! lol
A drill bit and a drill press. It's not a big deal. No special machining required.
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Old 05-19-2017, 01:14 PM   #19
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This is the used D30 gears I got. Not sure if anyone here could tell if they're young and worthwhile installing or not.









I absolutely wouldn't hesitate to install them. They will be fine BUT installing used gears is slightly different than installing a new set of gears. A new set of gears you are trying to produce the perfect oval contact patch in the center of the drive and coast side of the ring gear. On a well broken in set of used gears you are trying to achieve a pattern that resembles as close as possible the original wear markings from the previous setup. Not impossible or that difficult. You are just looking for 2 different things.
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Old 05-19-2017, 01:34 PM
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The regear shop told me that they are indeed equipped to drill the holes out bigger; I was just worried because I keep reading that "oh you better watch out! the Detroit TrueTracs are made out of UNDRILLABLE SUPERMETAL!"

And in regards to the used front gear they just told me that they can install it but they wouldn't be able to warranty their work - which is a risk I'm okay with, they seem to know what they're doing.
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Old 05-20-2017, 07:57 PM   #21
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The torque peak is pretty flat down to 1900 according to the chart they put out when they switched to the 3.6
I set the cruise at 55 and got like 17.5 mpg on a slight incline. Got like 20.5 mpg when I went back and did it in 6th. There's a lot more horsepower on tap in 5th at like 2400 rpms than there is in 6th at like 1900, but if you're just cruising and not accelerating you don't need it.

I tried it again on a steep grade and did get better mileage in 5th vs 6th, about 13 mpg vs 12. So under greater load it's better to have the rpms higher. I guess it comes down to what conditions you drive in most. If the rubicon got better mileage with 4.10s than 3.73s in every situation they probably wouldn't offer it with 3.73s
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Old 05-21-2017, 12:11 AM   #22
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Mine came with 3.73's and they are OK with the 33.3 RT's but if I could I would regear to 4.38's or something like that. The 3.6 red lines at 6200 so easy highway at 70 could be 2100+.
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Old 05-22-2017, 01:15 PM
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So I think I've settled on the 3.73s and a rear elocker. open front.

I've toyed with the idea of truetracs but I've spent days reading a decade worth of threads and conflicting options.

At the end of the day, the single rear selectable got me through everything in my last jeep. No need to delve into the unknown just for the hell of it.
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