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Discussion Starter · #1 ·
And this week, the Jeep is going from the stock 3.21 gears to 4.10 gears:

New rear Yukon "Dura Grip" limited slip rear diff with ring gear already installed:


New front Yukon "Zip" air locker with ring gear already installed:


The same shop just installed 4.56 gears and air-actuated Ox lockers front and rear on my son's Jeep Cherokee. They do real good work! I'm looking forward to driving my Jeep with the new diffs & gears!

Guy
 

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Well, gas mileage is right out the window now...but ya should be able to climb walls with it though.:driver:
 
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You will really enjoy the improvement in traction...
I run Detroit lockers + 4.56 axle gears front and back in my TJ with 33's....

Offroad - it's fun to have LOTS of traction....

The other day - I was out at the hunting lease... One of the younger guys on a 4-wheeler got stuck trying to follow me through a cut-over....

Thanks
 

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Discussion Starter · #4 ·
Well, gas mileage is right out the window now...but ya should be able to climb walls with it though.:driver:
I'll let you guys know how it does, but I don't think it's going to be all that bad. The 2012 JK has a six-speed manual. I can't even really use 6th until I'm doing about 70 mph now, it's a pretty tall overdrive gear. Believe fifth is also an overdrive ratio, though I can't remember for sure. Stock, the Jeep averages about 21 mpg out on the open road, and 15 or so in town or up in the hills. I suspect it's still going to do pretty well, even at the higher rpm's. We will see, and I'll report back either way; better or worse.

No doubt I should see some better traction and should be able to go slower & smoother in low range with the 4.10's. I'm running 32" tires now, and have room for 33's, no problem.

Guy
 

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With 4.10's and 33's it may get better mileage! Just being able to use all the gears at freeway speed's sometimes flat work's!
 

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That Caravan engine will probably like those low gears?, they need to wind a little tighter to make their power!
I went from the stock 3.54's in my TJ to 3.73's, the only reason I don't completely hate it is it gets exactly the same milage!?, the straight six has the low end torque to pull the higher gears.
 
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I'll let you guys know how it does, but I don't think it's going to be all that bad. The 2012 JK has a six-speed manual. I can't even really use 6th until I'm doing about 70 mph now, it's a pretty tall overdrive gear. Believe fifth is also an overdrive ratio, though I can't remember for sure. Stock, the Jeep averages about 21 mpg out on the open road, and 15 or so in town or up in the hills. I suspect it's still going to do pretty well, even at the higher rpm's. We will see, and I'll report back either way; better or worse.

No doubt I should see some better traction and should be able to go slower & smoother in low range with the 4.10's. I'm running 32" tires now, and have room for 33's, no problem.

Guy
It might actually help your gas mileage since you have tires that are taller than the factory spec tire....
 

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Discussion Starter · #8 ·
Yeah, this is the 2012 "Pentastar" V6, a new motor that year with 285 hp. Peppy little rascal, but it revs a bit to get to the power. Something like 75 or 80 hp more than the 3.8 liter V6 Jeep was using in the "JK" series Wranglers for a few years.

The Rubicon variants come standard with 4.10's and lockers front & rear, but my base model Jeep came with the 3.21's and open diffs. Fixing that this week! :biggrin:
 

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Yeah, this is the 2012 "Pentastar" V6, a new motor that year with 285 hp. Peppy little rascal, but it revs a bit to get to the power. Something like 75 or 80 hp more than the 3.8 liter V6 Jeep was using in the "JK" series Wranglers for a few years.

The Rubicon variants come standard with 4.10's and lockers front & rear, but my base model Jeep came with the 3.21's and open diffs. Fixing that this week! :biggrin:
What update do you have to make so the speedometer isn't off?
 

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Discussion Starter · #10 ·
I'm going to see about that. Was told by one source, that the speedometer feed on these newer Jeeps comes from the axle speed, not off the transmission, so the gearing change shouldn't change the speedo reading. We will see... I should have the Jeep back in my hands Friday.

Meanwhile, it's tough, but I just have to take the motorcycle everywhere I want to go.... :biggrin:

My son just had his 3.54's changed to 4.56's, at the same shop, and his speedometer is way off. His is a 1998 Jeep Cherokee though. He's actually doing about 50 mph when his speedometer reads 60 mph now. Apparently there's a different speedometer gear he needs.

Guy
 

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I'm going to see about that. Was told by one source, that the speedometer feed on these newer Jeeps comes from the axle speed, not off the transmission, so the gearing change shouldn't change the speedo reading. We will see... I should have the Jeep back in my hands Friday.

Meanwhile, it's tough, but I just have to take the motorcycle everywhere I want to go.... :biggrin:

My son just had his 3.54's changed to 4.56's, at the same shop, and his speedometer is way off. His is a 1998 Jeep Cherokee though. He's actually doing about 50 mph when his speedometer reads 60 mph now. Apparently there's a different speedometer gear he needs.

Guy
I think it's usually a gear inside the transfer case..... I think.
 

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With your 6 speed transmission I bet it will not only be awesome off road but on the road it will have some fantastic get up and go that will be more fun to drive than ever.Your rpm will tach higher at the same speed but with that transmission should not hurt gas mileage to much.Have fun this weekend it should be a blast! Mike
 

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Discussion Starter · #13 ·
Got her home from the diff shop today. Mostly done. I still need to run the wiring for the front air locker. Have a compressor mounted under the hood, but haven't wired it up yet.

Rear limited slip diff seems to be working great. Very smooth on the street. I've driven rigs with limited slip rear diffs for a lot of years now and I like the way they handle. If this one behaves like other good, aftermarket limited slips have for me in the past, it will add a lot of traction on loose surfaces off-pavement.


The 4.10's seem like a good fit for the Wrangler. At 60 mph on the highway, was turning about 2300 rpm's in 6th gear. Very nice and smooth and about 500 rpm higher than before. In town, taking off from a stop, the Jeep just leaps forward effortlessly, without slipping the clutch. BTW, the speedometer wasn't affected by this at all. In these newer vehicles it's a different sensor rather than a gear coming from the transmission like it was in years gone by.

Am supposed to take it real easy on the gears the first 100 miles, only short trips, and no hard acceleration or four-wheel drive. Up to 500 miles I can drive pretty much normally, but was told to still avoid long highway trips and not to drive real hard as the gears wear in.

Guy
 

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Got her home from the diff shop today. Mostly done. I still need to run the wiring for the front air locker. Have a compressor mounted under the hood, but haven't wired it up yet.

Rear limited slip diff seems to be working great. Very smooth on the street. I've driven rigs with limited slip rear diffs for a lot of years now and I like the way they handle. If this one behaves like other good, aftermarket limited slips have for me in the past, it will add a lot of traction on loose surfaces off-pavement.


The 4.10's seem like a good fit for the Wrangler. At 60 mph on the highway, was turning about 2300 rpm's in 6th gear. Very nice and smooth and about 500 rpm higher than before. In town, taking off from a stop, the Jeep just leaps forward effortlessly, without slipping the clutch. BTW, the speedometer wasn't affected by this at all. In these newer vehicles it's a different sensor rather than a gear coming from the transmission like it was in years gone by.

Am supposed to take it real easy on the gears the first 100 miles, only short trips, and no hard acceleration or four-wheel drive. Up to 500 miles I can drive pretty much normally, but was told to still avoid long highway trips and not to drive real hard as the gears wear in.

Guy
Nice!!

Did they say to come back after 500 miles so they can check the new gears?
 

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Discussion Starter · #15 ·
Yup. Shop owner is real particular about his work. He wants to check everything in about 500 miles, and put in new gear lube at that time too.
 

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Yup. Shop owner is real particular about his work. He wants to check everything in about 500 miles, and put in new gear lube at that time too.
I like how you chose to set it up with a limited slip in the rear and an air locker up front. Driving on the pavement won't be compromised and a locker in the front will pull it through a lot of crap off road.
 

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Discussion Starter · #17 ·
130+ miles on it since the gear change. Report:

Gear ratio change did not affect the speedometer at all. It's still 2 mph off at an indicated 45, just like before the change. Police radar board has me at 47 when speedometer reads 45.

Love the 4.10's! No more clutch slipping to get going. Let out the clutch, and the Jeep leaps forward! At about 60 mph I'm seeing 2300 rpm on the tach. Very nice, and lets me use 6th gear on our two-lane highways. No more downshifting for normal hills out on the highway.

It's still early, with few miles accumulated, but the on-board computer is indicating 16.5 mpg average, for mixed in-town, up in the hills, and two-lane highway driving. That's about 1.5 mpg BETTER than I was getting with the old gear ratio. Huh.

The rear limited slip is working great. Very smooth. Occasionally when making a turn and accelerating I get a little chirp from the inside rear tire. Otherwise I barely notice it on dry pavement. Out in the rough stuff, between the gears and the diff, I'm climbing steep, loose hills in first & second gear, two-wheel drive... The same hills I used to go into 4-low to climb! That's what I was after!

Re the front locker, we're setting it up a little different than originally planned, so it's not yet hooked up to the underhood air compressor. Maybe by mid June? We will see.

So far am very impressed with both the new gear ratio and the new rear limited slip diff.

Guy
 

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130+ miles on it since the gear change. Report:

Gear ratio change did not affect the speedometer at all. It's still 2 mph off at an indicated 45, just like before the change. Police radar board has me at 47 when speedometer reads 45.

Love the 4.10's! No more clutch slipping to get going. Let out the clutch, and the Jeep leaps forward! At about 60 mph I'm seeing 2300 rpm on the tach. Very nice, and lets me use 6th gear on our two-lane highways. No more downshifting for normal hills out on the highway.

It's still early, with few miles accumulated, but the on-board computer is indicating 16.5 mpg average, for mixed in-town, up in the hills, and two-lane highway driving. That's about 1.5 mpg BETTER than I was getting with the old gear ratio. Huh.

The rear limited slip is working great. Very smooth. Occasionally when making a turn and accelerating I get a little chirp from the inside rear tire. Otherwise I barely notice it on dry pavement. Out in the rough stuff, between the gears and the diff, I'm climbing steep, loose hills in first & second gear, two-wheel drive... The same hills I used to go into 4-low to climb! That's what I was after!

Re the front locker, we're setting it up a little different than originally planned, so it's not yet hooked up to the underhood air compressor. Maybe by mid June? We will see.

So far am very impressed with both the new gear ratio and the new rear limited slip diff.

Guy
Sweet!! I figgered you would probably get a little bit better gas mileage.... Yeah I have to be careful going around a corner with my foot on the gas pedal. The rear locker will engage and make the truck go a little sideways.... especially when it's wet:biggrin:
 
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