JLUR - 37" tire risks

[Ratbert]

I'm amazed how many jeep people run D30/D35 axles with 37s and don't seem to have problems. I would think the Rubicon trail would eat them, but I seem to be wrong.

Good point. I sometimes forget that lower-end variants lack the beefier axles.

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[Ratbert]

I broke a Dana 35 rear axle shaft on a '95 YJ once while pulling out of a gas station. I wasn't even giving it the gas beyond just normal mellow acceleration. No tire spin or other shenanigans, just pulling out and turning at the same time. I hear a loud bang and feel the rear of my YJ shift. When I looked in the passenger side view mirror, I see my tire and wheel about 6" out from the fender flare, so I pulled over and stopped before it came all the way out.

Stupid question, but lockers weren't engaged?

 

[3TV]

Stupid question, but lockers weren't engaged?

This was a bone stock YJ with no lift, no lockers, and 30x9.50 tires.

 

[Zandcwhite]

I think you're right about that on the later JLs with the rear "full float" axles.

My approach on the D44s on my 2018 is to put in chromoly axles and mitigate the probability of having a failure on the trail. I could deal with a ring and pinion failure easier on the trail than an axle failure. That's because, although I have spare axles, I rarely carry them in the Jeep, but they are sometimes at or near the trailhead, along with spare driveshafts, tierod, draglink, trackbar, D44 differential, etc.

I'm not sure I'm seeing how you'd deal with a r&p easier than an axle shaft? You'd have to do at least twice the work (removing both axle shafts) just to get the carrier out. Even if you have a spare carrier and ring and a pinion you aren't exactly just dropping parts in like a new axle shaft. You'd be pressing bearings on to the pinion on the trail? Or do you carry a fully set up spare with the shims, bearings, preload all set up and then removed from your axle? Or are you saying you could just limp it out by pulling the rear driveshaft and hoping a broken tooth doesn't suddenly wedge between the gears at any kind of speed? In the wife's old wj we blew up the rear and a chunk of the spider gear went through the cover. Much more involved repair than the broken shaft on the same rig on a different rubicon trip. After dealing with those 2 failures we ended up swapping in a 13 bolt (shaved 14 bolt) full float with disc brakes and never had to worry about it again. Personally I'll take a shaft over gears every time.

 

[grimmjeeper]

This was a bone stock YJ with no lift, no lockers, and 30x9.50 tires.

That wasn't entirely uncommon in the YJ and TJ. Even the XJ/MJ had the same weak Dana 35.

The YJ never got an upgrade but the TJ had an optional Dana 44. The XJ/MJ got a Dana 44 early on, and they changed to a Chrysler 8.25 instead.

The biggest problem with the Dana 35 (and early Chrysler 8.25) is the 27 spline shafts. They're tiny and weak. The later 8.25 upgraded to 29 spline, while the Dana 44 has 30 spline.

The M200 in the JL has 29 spline shafts and a bigger ring and pinion so it's not nearly as weak as the old Dana 35. It's not as strong as an old Dana 44, or the newer and stronger M220 (with 32 spline shafts and a pinion shaft almost as big as a Dana 60).

 

[roaniecowpony]

I'm not sure I'm seeing how you'd deal with a r&p easier than an axle shaft? You'd have to do at least twice the work (removing both axle shafts) just to get the carrier out. Even if you have a spare carrier and ring and a pinion you aren't exactly just dropping parts in like a new axle shaft. You'd be pressing bearings on to the pinion on the trail? Or do you carry a fully set up spare with the shims, bearings, preload all set up and then removed from your axle? Or are you saying you could just limp it out by pulling the rear driveshaft and hoping a broken tooth doesn't suddenly wedge between the gears at any kind of speed? In the wife's old wj we blew up the rear and a chunk of the spider gear went through the cover. Much more involved repair than the broken shaft on the same rig on a different rubicon trip. After dealing with those 2 failures we ended up swapping in a 13 bolt (shaved 14 bolt) full float with disc brakes and never had to worry about it again. Personally I'll take a shaft over gears every time.

My statement was prefaced with not having spare axles on site. A broken ring gear can be removed so it can roll and be propelled by the other axle or be towed and still support the vehicle. A broken axle will leave the inboard end unsupported which will allow the axle to tip and bind the brake, etc, etc, etc.

 

[Maverick909]

We bought our JL with a 3.5" lift and 37" tires already installed and since we got it I keep hearing 2 different stories...
1) JL Rubicon with a lift can fit 37" wheels and there should be no issues as long as you aren't going crazy climbing vertical walls or rock bouncing.
2) 37" tires without regearing or replacing axles is sure to break something.

Can any of you who perhaps have experience give me your advice?
A) Are 37" tires ok on factory JL Rubicon running gear?
B) If upgrades are necessary, what is the minimum that I have to do to not break something on mild trails?

PS this is the lift kit that was installed, if this is any help...
ReadyLIFT | 2018-2019 Jeep JL Wrangler 2-Arm Terrain Flex Lift Kit

I would suggest figuring out your gearing for your axles. The auto handles more then the manual transmission does but also comes with higher load and more temperature in the oil. I would recommend 4.88 gears for 37’s. I’ve been 37’s. For two years on rubicon axles with 4.88 Yukon gears. Jeep has done great with everything I’ve thrown at it. Including just completing the rubicon trail. If you stick to moderate to easy trails 37’s on rubicon axles should last you a very long time. Just keep up with maintenance and make sure you have the correct gearing for the tire size to help the transmission with the work load.

 

[BigDill]

To your question about 37s with stock running gear, there are those that do it and say it works fine and there are some that have had failures. One common failure is twisted rear axles. The front axle shaft failures from large tires are usually a U-joint failure from applying power while turned sharply. It just takes a lot more torque to turn larger tires. Installing chromoly axle shafts add a lot of margin for preventing an axle shaft failure. The other failures of the axles is the bent or broken housing. This happens from big impacts or bounces. It's all about the driving style and a bit of luck. If you drive hard, you can break the Rubicon D44 axles. But, if you're conservative, you may not have anything to worry about, even on some pretty tough trails.

Thank you, Ill keep it mild til I have upgrades in the budget, then replace he weakest links as I break them. That sounds like the consensus of what I have been hearing in hear, online, and out in the world.

 

[kah.mun.rah]

We bought our JL with a 3.5" lift and 37" tires already installed and since we got it I keep hearing 2 different stories...
1) JL Rubicon with a lift can fit 37" wheels and there should be no issues as long as you aren't going crazy climbing vertical walls or rock bouncing.
2) 37" tires without regearing or replacing axles is sure to break something.

Can any of you who perhaps have experience give me your advice?
A) Are 37" tires ok on factory JL Rubicon running gear?
B) If upgrades are necessary, what is the minimum that I have to do to not break something on mild trails?

PS this is the lift kit that was installed, if this is any help...
ReadyLIFT | 2018-2019 Jeep JL Wrangler 2-Arm Terrain Flex Lift Kit

You aren’t going to break anything on mild trails with mild driving. People can break axles with any size tire driving it hard into objects. Just be smart. A regear isn’t necessary but will allow your Jeep to shift gears sooner.

 

[Zandcwhite]

My statement was prefaced with not having spare axles on site. A broken ring gear can be removed so it can roll and be propelled by the other axle or be towed and still support the vehicle. A broken axle will leave the inboard end unsupported which will allow the axle to tip and bind the brake, etc, etc, etc.

Got it. Towing a 2wd rig through a trail like the rubicon sucks. It's also very hard on the other rig/ rigs. That quickly turns into more broken parts. I'd rather run to town and pick up an axle shaft than drag a half broken 5k+ pound Jeep through the trail from experience. I've made an overnight run from Rubicon springs up Cadillac hill and all the way home for parts. Had the axle shaft in the WJ by 11am the next morning. We've also left the WJ on the trail once and my XJ another time after breaking parts we didn't have a way to fix. The xj master cylinder went out and I wasn't going to take on Cadillac hill in an auto with no brakes. The WJ lost a tie rod end at the drag link which then got folded back around the axle. There was no fixing that pretzel and getting it off the trail with no steering wasn't going to happen. I find it's better to repair in place even if it means extra miles on the other rig.

 

[roaniecowpony]

Got it. Towing a 2wd rig through a trail like the rubicon sucks. It's also very hard on the other rig/ rigs. That quickly turns into more broken parts. I'd rather run to town and pick up an axle shaft than drag a half broken 5k+ pound Jeep through the trail from experience. I've made an overnight run from Rubicon springs up Cadillac hill and all the way home for parts. Had the axle shaft in the WJ by 11am the next morning. We've also left the WJ on the trail once and my XJ another time after breaking parts we didn't have a way to fix. The xj master cylinder went out and I wasn't going to take on Cadillac hill in an auto with no brakes. The WJ lost a tie rod end at the drag link which then got folded back around the axle. There was no fixing that pretzel and getting it off the trail with no steering wasn't going to happen. I find it's better to repair in place even if it means extra miles on the other rig.

I'm onboard with that philosophy. I bring all four OEM axle shafts and other spares in my tow rig and leave it in Pollock Pines.

 

[acomputernerd]

I’ve had 37’s on mine. Went one year without a regear and wished I had done it sooner. Manual transmissions are really affected by the gearing. The ball joints only lasted a year as well. You have to pull the axles to replace them so I slid in rcv axles. I did it all when I regeared. I just a few months ago replaced all of the linkage arms. I also wheel it hard but am not a fan of the skinny pedal so that has helped. Wheeling lighter trails with 37 gets boring fast so be prepared to wheel harder trails as well. Basically just save up and buy the parts on a Black Friday special. Have loads of fun!

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