Are 37's to much for stock Rubicon axles to handle? - JeepForum.com
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post #1 of 23 Old 07-22-2019, 10:19 AM Thread Starter
Hardrock2015
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Are 37's to much for stock Rubicon axles to handle?

I have a 2015 Rubicon Hardrock with a 3.5" rock krawler lift, am currently running 34" falkens. It seems my mpg couldnt get much worse and I would love 37's when I go wheeling just dont wanna doom my stock axles. I see plenty of people running them but dont know if said folks are on upgraded axles. Would love to hear of any examples or advice from my fellow jeep lovers.
Thanks for reading, happy jeeping!

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post #2 of 23 Old 07-22-2019, 04:00 PM
FastCarGuy11
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I'll be curious to see what others have to say on this as well. I do know a number of people running 37's on mild trails with no issues. Several have installed the EVO gussets on the front and a truss on the rear for added protection.
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post #3 of 23 Old 07-22-2019, 05:49 PM
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Ive run 37 Pitbulls on a D30 for a couple years without a break. Then switched over to a HD D44 housing and promptly snapped both front axles.

- Moral of the story, drive within your means and equipment..

You can wheel 37s for years on a D30 as long as you mind the skinny pedal. Or you can be one of those guys that can break a Dana60 on 33s. Your choice.


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post #4 of 23 Old 07-22-2019, 06:26 PM
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there is a lot to that "driver" part. Our JKr is a 2 door and for the amount of armor is still lighter them most.

the real issue is the long side tube on the front axles. wont matter if its a 30/d44 all jks stuff. that tube can break i have had two in our jeep club break them in the same exact place, exact. Now one did have a arctic front truss the other stock. both broke right under the spring pad. This is real life on trails we do. The two jeeps here dont really wheel as many hard trails as i do and lead in the club. Since i know how they drive and they are not bouncing type right footers. Crack is fatigue based and might even have to do with welding the bracket on for springs perch from the factory. hard to say. No matter i sleeved mine and did the Cs for the F of it. We wheel a lot and have to say i dont see C's bending really. none issue for where i have been. I do my own work so welding and such dont cost me anything. well consumables. metal and such.

the axles and size of a JKd44 ring and rubi ones have more splines as well larger bearings. seem to do well against 37s. The week link is as it is the U joint with Cromo axles. But they only tend to pop when at lock in a bind and to much foot. In say 5 years of 37s close to on this jeep. Trails are Fordyce , Rubicon now 4x, Dusy 3x should get in a run in a month here will be 4th running. In this jeep. As well winter its wheeled here in AZ on nothing but trails that are harder then those. Just short and rough and many.

steering is a big issue in a jk on 35s on hard trails and 37s its a joke really. Only two ways around it. Hydro assisted. Or that PSC big bore box. you wont have to worry about the cheap fiat one break the sector on that thing. but hydro would be better. i went with the box and its ok for 37s not larger. it wont break no way but would get hot when the pump gets hot.

gears. if street you will need at least 4.56 with the auto Min.. to even think about being in the stock zone for power towing 4.88/ mpg. Now on our Rubi it was ordered with 4.1 and the W5 auto. But its a two door and no top, no doors no stock seats, no rear seat. no inside interior. Only the dash. Delete list is long. No air bags or stock seat belts. the thing with no gear change in it does rather well on 4.1s and 37s. But i dont do much street as well and when i do. yea no way it could tow. 5th is way to fast to use ;down hill. and the mpg is around 14. it was on 35s getting 18 with 4.1s. off road in rubi 4 low its rather good.
For street 37s? To me why? I cant see it. the tire cost to much to wear on the pave. other wear items like Bjs and such.
here it is loaded down end of this June with a ton of stuff. that lift is a 4.5 but with all the gear for Rubicon. weeks gear, wife two dogs. Is hard on axles when the weight is on them.

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post #5 of 23 Old 07-23-2019, 08:27 AM Thread Starter
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Those are some great points and you got some serious mods . It's not that I want 37 to drive on the road. Just thought that my gas mileage was already tanked I might as well jump up to a taller tire to make it nicer while off-roading. I live in Washington State about 10 MI from a hardcore ORV Park called elbe Hills. A lot of people that frequent the area run 40s and even taking bypasses and missing real hard stuff I need all the clearance I can get. My jku has not let me down it's a completely amazing vehicle. I try not to beat on it but have tested my door seals a few times. Thanks for sharing some of your knowledge
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post #6 of 23 Old 07-23-2019, 08:29 AM Thread Starter
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post #7 of 23 Old 07-23-2019, 10:08 AM
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I run a stock D44 rear and a Core 44 Front axle housing. I have replaced all the axle shafts with Chromolly shafts, RCV in the front, Revolutions in the rear. ARB front and rear and 4.56 gears. I recently upgraded to a PSC Big Bore PS pump, cooler and reservoir. Turning locked 37's with the stock gear doesn't happen. You will go thru ball joints and steering gear. I run a Fusion 4x4 2.5 Ton Tie Rod setup, Currie Correctlync Drag link and G2 Ball Joints.

I have been running 37's now for about 6 months. I would recommend 4.88 gears though, 4.56 is slightly under geared if you do any mountains. I don't baby mine and at this point, all is good.

Gratuitous wheeling shot from this last weekend.
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post #8 of 23 Old 07-25-2019, 07:52 AM
rcoe
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Don't forget brakes, my stock brakes were barely enough for 35's.
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post #9 of 23 Old 07-25-2019, 09:12 AM
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40s on the street is dumb. wall crawler look at me type. 30 days im off to run the Dusy Ershem. 5 days on the trail. Cali guys rate it a 10, Az would call it a 4. 32 miles this will be the jeeps 4th running of it........

even our tow rig is only on 35s the wifes DD 7.3 4x4 Excursion. My f250 7.3 is a 2x4 my DD and its one 33s. Towing the jeep on a trailer they both do 12/13 at 75mpg in the 1200 mile run to say Rubicon round trip. that has steep mountains grades. the jeep gets 14 and is slower then the wifes 4 ton Excursion. pluss jeep suck after being init say 5 days , dirty . nice to get in a large truck for the ride home. Im old and been doing this since 1975. Jeeps are not DD to me much. here in town i might take it out once a month to the part store. buts this town is like 3 miles any direction. You left town.

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post #10 of 23 Old 07-25-2019, 10:16 AM
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Quote:
Originally Posted by rcoe View Post
Don't forget brakes, my stock brakes were barely enough for 35's.
What you said!

Going to 37's will require the Mopar Big Brake Kit. The Crown kit is exactly the same kit at a lower cost.

You need a minimum wheel size of 17" for a BBK.

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17 WK2 Trailhawk
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post #11 of 23 Old 07-25-2019, 10:41 AM
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I even recommend the BBk for 35's. Really, is there ever a downside to better stopping?
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post #12 of 23 Old 07-25-2019, 01:17 PM
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Quote:
Originally Posted by motoguy1251 View Post
I even recommend the BBk for 35's. Really, is there ever a downside to better stopping?
No, there isn't.

I had my BBK on 35's first. It made a huge difference in stopping power. On 37's, it's a must do.

06 KJ
12 JK, 2.5" Teraflex lift, Bilstein 5100's, BFG KM3's 37x12.5/R17
17 WK2 Trailhawk
KN4BBA
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post #13 of 23 Old 07-26-2019, 04:48 PM Thread Starter
Hardrock2015
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Oh yes after brakes got brought up it seems that would be a better place to start as my girl doesn't like to stop in a hurry as it is. Havent done much research on brake upgrades but the little I have done seem there is plenty of options. Thanks again for all the help!
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post #14 of 23 Old 08-04-2019, 04:37 PM
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I run 37s on my stock Rubi housings. I have added the Mopar BBK, Revolution axle shafts front and rear, Currie Extreme tie rod, Currie HD drag link, Teraflex ball joints and welded the Cs.

I have not had any issues so far. I dont DD my JKUR, but I do drive to and from trails.

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post #15 of 23 Old 08-13-2019, 07:57 PM
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Quote:
Originally Posted by Hardrock2015 View Post
I have a 2015 Rubicon Hardrock with a 3.5" rock krawler lift, am currently running 34" falkens. It seems my mpg couldnt get much worse and I would love 37's when I go wheeling just dont wanna doom my stock axles. I see plenty of people running them but dont know if said folks are on upgraded axles. Would love to hear of any examples or advice from my fellow jeep lovers.
Thanks for reading, happy jeeping!
Lots of them out there with 37s on the stock Rubi axles. The rear housings are way beefy, can easily hand;e 37s. The axle shaft at the flanges may bend, at whch time throw in some Ten FActory, etc. You have an upgraded front housing (thicker diameter tubes) that can handle them just fine.

Your issue will be the gearing. Even with a 3.6L and the five speed auto box with the optional 4.10 gears you'll notice the loss of aceleration power. A swap out to 4.88s on a 3.6L works great. On the earlier 3.8L 5.13s - 5.38s are called for.

I've street driven and wheeled my '09 JKUR for 10 years on 37s, go for it and don't look back!
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