Need Advice on 2012 JKU 3.6L Auto Regear And Towing Capacity

M

Meety Peety

New member
Hey guys, I'm new here and a little confused about the tow rating and gearing on my Jeep. I have a 2012 Unlimited Sport (3.6L Auto) which I always thought was geared 3.73 stock. I am getting ready to regear it and was planning on going to 4.88 (Already on 35's) and figured I might as well request a build sheet just to be sure I don't need to buy a new carrier. Well, Got the build sheet this morning and it says I have 3.21 gears and a tow package with trailer sway damping (But evidently not the "Max tow" package). Here's where I get confused.

I always thought ALL 2012 Unlimited Autos come with 3.73 gears stock? I have seen this posted a few times and in my manual (2012 edition) it doesn't even show an option listed for a 3.6L Auto with 3.21s. Reading a little bit online, I have seen a few people talking about early models (Mine is 3/7/12) coming with 3.21s stock unless you buy the "max tow" package and that even with the standard tow package you can end up with 3.21s. I bought this Jeep used in 2014 and wasn't aware of this at the time, just figured tow package was good to go. At the time, I had no plans to tow with this vehicle. I am OK with buying a carrier when I do the regear, but I am now wondering what else may affect my tow rating (Or my ability to tow) even after the regear? Since I don't even see a 3.21 Unlimited Auto listed in my manual for towing capacity, is it fair to assume that my rating will be 3500# if I regear to 4.88/35 (Closer to the equivalent of 3.73/stock tire)? The only 3.21 Unlimited I see is a Manual trans rated at 1000# - a major drop from the 3500# I was expecting from "All Unlimited models" shown on the Jeep website. Is this solely due to the gearing of the Jeep or is there more to it than that? I'm also a bit confused as to why they would sell a Jeep with 3.21s and a tow package but not acknowledge it in the manual, especially in terms of towing capacity (the liability that comes along with exceeding this).

I am going to go home today and throw it on jacks to see if I can figure out my current gearing the hard way, but I'm not sure where to go from here. Assuming that I had 3.73s, I went on a "test run" with a 1700# (empty) flatbed trailer last weekend and did less than stellar and power was definitely lacking. No issues with stopping or sway, just a serious lack of power. The transmission was hunting pretty bad and going up some steeper grades the RPMs were out of my comfort zone. I was hoping that a regear would fix it, but now I'm questioning my GVWR and GCWR capabilities too? My GVWR is listed on the door sticker, but GCWR is only shown in the manual, and there is no value for my apparent configuration. For what it's worth, I'm only looking to pull about 2000# combined trailer weight but will be going up a couple of mild grades. Being so heavy (Bumpers, sliders, winch etc) and with the gear ratio that I currently have (I was wondering why 3.73s were THAT bad?) I already struggle a bit on steep grades without a trailer and would rather not over stress the vehicle if it just can't handle it.

Thanks in advance for any advice you can give me.
 
LarryG

LarryG

New member
Meety Peety said:
Hey guys, I'm new here and a little confused about the tow rating and gearing on my Jeep. I have a 2012 Unlimited Sport (3.6L Auto) which I always thought was geared 3.73 stock. I am getting ready to regear it and was planning on going to 4.88 (Already on 35's) and figured I might as well request a build sheet just to be sure I don't need to buy a new carrier. Well, Got the build sheet this morning and it says I have 3.21 gears and a tow package with trailer sway damping (But evidently not the "Max tow" package). Here's where I get confused.

I always thought ALL 2012 Unlimited Autos come with 3.73 gears stock? I have seen this posted a few times and in my manual (2012 edition) it doesn't even show an option listed for a 3.6L Auto with 3.21s. Reading a little bit online, I have seen a few people talking about early models (Mine is 3/7/12) coming with 3.21s stock unless you buy the "max tow" package and that even with the standard tow package you can end up with 3.21s. I bought this Jeep used in 2014 and wasn't aware of this at the time, just figured tow package was good to go. At the time, I had no plans to tow with this vehicle. I am OK with buying a carrier when I do the regear, but I am now wondering what else may affect my tow rating (Or my ability to tow) even after the regear? Since I don't even see a 3.21 Unlimited Auto listed in my manual for towing capacity, is it fair to assume that my rating will be 3500# if I regear to 4.88/35 (Closer to the equivalent of 3.73/stock tire)? The only 3.21 Unlimited I see is a Manual trans rated at 1000# - a major drop from the 3500# I was expecting from "All Unlimited models" shown on the Jeep website. Is this solely due to the gearing of the Jeep or is there more to it than that? I'm also a bit confused as to why they would sell a Jeep with 3.21s and a tow package but not acknowledge it in the manual, especially in terms of towing capacity (the liability that comes along with exceeding this).

I am going to go home today and throw it on jacks to see if I can figure out my current gearing the hard way, but I'm not sure where to go from here. Assuming that I had 3.73s, I went on a "test run" with a 1700# (empty) flatbed trailer last weekend and did less than stellar and power was definitely lacking. No issues with stopping or sway, just a serious lack of power. The transmission was hunting pretty bad and going up some steeper grades the RPMs were out of my comfort zone. I was hoping that a regear would fix it, but now I'm questioning my GVWR and GCWR capabilities too? My GVWR is listed on the door sticker, but GCWR is only shown in the manual, and there is no value for my apparent configuration. For what it's worth, I'm only looking to pull about 2000# combined trailer weight but will be going up a couple of mild grades. Being so heavy (Bumpers, sliders, winch etc) and with the gear ratio that I currently have (I was wondering why 3.73s were THAT bad?) I already struggle a bit on steep grades without a trailer and would rather not over stress the vehicle if it just can't handle it.

Thanks in advance for any advice you can give me.
Click to expand...

If you find you have 3.21 and want 3.73.....I just took mine out....you can have them cheap.
 
J

JKDream

Guest
Since you are no longer running factory tires, I would go deeper than a 3:73.
You'll want some low end torque to help get the trailer moving, especially up hills.
3:73 for 35s is still undergeared, and going to put a significant strain on your transmission.
From my understanding, the '12s came with 3:21's unless the Max Tow package was added (Rubicon is an exception).
My 13 came with 3:21s. I would be considering 4:56 - 4:88, depending if you have a true 35, or a 34 (315x70x17).
If you regear you will re-gain a proper tow rating. There's people on the forum towing travel trailers with JK's.
 
zimm

zimm

Caught the Bug
I'd go 4.56. I have factory 4.10's and "35's" which actually measure 33.75" tall. When they wear out, I want 37's and 4.88's. Don't go lower than 4.10...
 
Linebacker

Linebacker

Caught the Bug
zimm said:
I'd go 4.56. I have factory 4.10's and "35's" which actually measure 33.75" tall. When they wear out, I want 37's and 4.88's. Don't go lower than 4.10...
Click to expand...

X2! I'm running a stone stock 2012 with 4.10's. It's a good gear for stock but will go to 4.56 or 4.88 when the 35's go on. I like the power and mpg's of the 4.10's but the extra rolling resistance and 10% diameter increase of the 35's will probably push me toward 4.88's. :twocents:
 
M

Meety Peety

New member
Thanks for the input guys. I definitely wouldn't regear to 3.73 or even 4.10. I was originally planning to go 4.56 but had a lot of people suggesting 4.88. At the time, wrongfully assuming I had stock 3.73 gears I figured 4.56 might not be enough and leaned towards 4.88. Now a little less confident in that but still learning towards 4.88. Right now, the jeep is seriously underpowered.. but 3.21 to 4.88 seems like a big step. Not too worried about highway RPM/MPG because I'm a slow poke driver half the time anyway and probably won't do more than 65-70 all that much. I spend most of my time climbing hills where I'm stuck at 3.5k-4k rpms just trying to maintain 45 up the hill.. that is what I'm trying to get rid of. I gotta think that 4k up a hill every day is worse than 2.8k on a short stretch of highway at the end of my commute. My transmission must hate me.:grayno:

For towing, I'm OK with looking into trailer brakes, though never used them and not sure if i have the controller, probably not. Plenty of time to learn. I'm fine with new rotors/HD pads if that's all that's really wrong with them that would be great. My main concerns is making it up what I consider to be pretty modest grades without hunting for gears or watching my speedometer sink while rpms sail up.

So does it seem like 4.88s and HD rotors/pads will be enough to pull 2k# up a mild grade 10-12 times a year? What all is involved with installing a trailer brake controller?
 
J

JKDream

Guest
Meety Peety said:
Thanks for the input guys. I definitely wouldn't regear to 3.73 or even 4.10. I was originally planning to go 4.56 but had a lot of people suggesting 4.88. At the time, wrongfully assuming I had stock 3.73 gears I figured 4.56 might not be enough and leaned towards 4.88. Now a little less confident in that but still learning towards 4.88. Right now, the jeep is seriously underpowered.. but 3.21 to 4.88 seems like a big step. Not too worried about highway RPM/MPG because I'm a slow poke driver half the time anyway and probably won't do more than 65-70 all that much. I spend most of my time climbing hills where I'm stuck at 3.5k-4k rpms just trying to maintain 45 up the hill.. that is what I'm trying to get rid of. I gotta think that 4k up a hill every day is worse than 2.8k on a short stretch of highway at the end of my commute. My transmission must hate me.:grayno:

For towing, I'm OK with looking into trailer brakes, though never used them and not sure if i have the controller, probably not. Plenty of time to learn. I'm fine with new rotors/HD pads if that's all that's really wrong with them that would be great. My main concerns is making it up what I consider to be pretty modest grades without hunting for gears or watching my speedometer sink while rpms sail up.

So does it seem like 4.88s and HD rotors/pads will be enough to pull 2k# up a mild grade 10-12 times a year? What all is involved with installing a trailer brake controller?
Click to expand...

4:56 is a good choice for auto and 35s if you don't plan to go bigger.
4:88 is good as well, but you're a little overgeared at that point imo.
Still suitable for 35-37.
You are correct, you don't NEED the brake upgrade, but it doesn't hurt. I'd recommend looking into Dynatracs brake setup.
Trailer brake controller is pretty simple, basic wiring knowledge and you shouldn't have an issue installing it.
 
Journeyman

Journeyman

New member
Mopars makes a 7 pin wiring harness that's plug and play. Just follow the directions on the install. Around a 100$ I think. I would most definitely recommend trailer brakes if your towing 2k! Remember what goes up must go down and you can and will get into trouble a lot quicker going down hill than going up (I've done it [emoji33])
I would recommend the 4.88 if your just cruising around town and rarely getting on a freeway and cruising at 80. Especially if your towing 2k up a hill! Makes the re-gear worth while. And please get trailer brakes set up!!!!


Sent from my iPhone using WAYALIFE mobile app
 
Brute

Brute

Hooked
I would recommend trailer brakes...towed my trailer quite a bit this summer...coming down the mountain passes it made a big difference
 
zimm

zimm

Caught the Bug
Meety Peety said:
Thanks for the input guys. I definitely wouldn't regear to 3.73 or even 4.10. I was originally planning to go 4.56 but had a lot of people suggesting 4.88. At the time, wrongfully assuming I had stock 3.73 gears I figured 4.56 might not be enough and leaned towards 4.88. Now a little less confident in that but still learning towards 4.88. Right now, the jeep is seriously underpowered.. but 3.21 to 4.88 seems like a big step. Not too worried about highway RPM/MPG because I'm a slow poke driver half the time anyway and probably won't do more than 65-70 all that much. I spend most of my time climbing hills where I'm stuck at 3.5k-4k rpms just trying to maintain 45 up the hill.. that is what I'm trying to get rid of. I gotta think that 4k up a hill every day is worse than 2.8k on a short stretch of highway at the end of my commute. My transmission must hate me.:grayno:

For towing, I'm OK with looking into trailer brakes, though never used them and not sure if i have the controller, probably not. Plenty of time to learn. I'm fine with new rotors/HD pads if that's all that's really wrong with them that would be great. My main concerns is making it up what I consider to be pretty modest grades without hunting for gears or watching my speedometer sink while rpms sail up.

So does it seem like 4.88s and HD rotors/pads will be enough to pull 2k# up a mild grade 10-12 times a year? What all is involved with installing a trailer brake controller?
Click to expand...

I'd go 4.56. 4.88 and you'll be screaming on the highway. The difference from 3.21 to 4.56 will be HUGE.

Trailer brakes are more important than just upgrading the jeep brakes. You'll have 2 more tires helping slow down the jeep. Also, if the trailer comes off, it'll stop on it's own, which is a nice safety feature. There's only 4 wires to hook up:

Black - Battery Power
Red - Stoplight Signal
White - Ground
Blue - Output to trailer (connects to blue wire on mopar 7 pin harness)

The brake controller (I recommend a P3) has a sensor in it that applies the brakes automatically.

Here's the P3: http://www.tekonsha.com/products/br...trollers/p3-/TzaIxkVx1cI5XOy!osRB55TR19SXShj4

There's a link to the install manual on that page too.
 
M

Meety Peety

New member
Thanks guys. I will look into trailer brakes next after the regearing. I haven't picked a trailer yet and I was trying to keep it as small and light as possible.. unfortunately not a whole lot of small and light aluminum trailers come with preinstalled trailer brakes. So I'll probably end up with a standard trailer and have to add them. Anything I should look out for when picking one? All I've seen is that you should look for one with a preinstalled mounting plate. What about axle type, wheel size, overall ride height etc.. will any of that come into play when brakes come into the equation or is a trailer a trailer as far as brakes are concerned? I was looking to get a taller trailer if possible to minimize the amount of drop at the tongue.
 
tucked

tucked

Member
I have 4.88's on my 2015 JKU, Automatic with 35's. I towed a 5x10 converted cargo trailer to California and back through mountains and regret not going with 5.13s. If it were me I would not go with 4.56, but rather 4.88 or 5.13.
 
J

JKDream

Guest
tucked said:
I have 4.88's on my 2015 JKU, Automatic with 35's. I towed a 5x10 converted cargo trailer to California and back through mountains and regret not going with 5.13s. If it were me I would not go with 4.56, but rather 4.88 or 5.13.
Click to expand...

5:13 is too low. I ran it for almost a year on 35's.
~70mph was 3200rpm.
It depends whether he wants a bit of additional power (4:88), or the closest to stock gearing (4:56).
 
jorgelrod

jorgelrod

Hooked
35's and 4.56 is more like stock at 3.73. Go with 4.88 if you will be towing constantly or want to feel like stock with 4.10. Needless to say, RPM on the highway will be higher, but negligible at a 200-300 rpm difference...
 
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M

Meety Peety

New member
Yea, I think I'm going to go with 4.88. I won't be towing a LOT but when I do, I think I will appreciate the extra power. Although this is still my daily driver, even when I'm on the "highway", a good part (more than 60% I'd say) of my commute is up and down hills. So most of my commute is currently spent struggling up a hill then coasting down it, not a whole lot of straight flat freeway on my day-to-day. For the times when I am on flat ground, I don't mind cutting back to 60-65 to keeps the RPMs happy. Hell, I spend half my commute north of 3.5k as it is while trying to climb hills in second.. so what harm is 2.8k-3k going to do.

Thanks for all the input and wisdom guys
 
kbsvo2go

kbsvo2go

New member
Just keep in mind your tow rating provided by Jeep has a lot more engineering involved than just gearing and brakes. I believe it's a sum of frame structure (strength) wheel base etc. We've all seen people do it but that doesn't make it safe for you or the other people on the highway around you. I've seen 1/2 tons trucks with fifth wheel hitches and a 35 ft trailer and think to myself "I hope I'm not in front of him on a long down hill grade"


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maxspongebob

maxspongebob

Member
Journeyman said:
Mopars makes a 7 pin wiring harness that's plug and play. Just follow the directions on the install. Around a 100$ I think. I would most definitely recommend trailer brakes if your towing 2k! Remember what goes up must go down and you can and will get into trouble a lot quicker going down hill than going up (I've done it [emoji33])
I would recommend the 4.88 if your just cruising around town and rarely getting on a freeway and cruising at 80. Especially if your towing 2k up a hill! Makes the re-gear worth while. And please get trailer brakes set up!!!!


Sent from my iPhone using WAYALIFE mobile app
Click to expand...

Agreed. I would recommend 4.88 and brakes.
 
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