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Thread: UJoint Considerations for Axle Upgrade

  1. #1
    Hooked Noble Woodsman's Avatar
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    UJoint Considerations for Axle Upgrade

    I know this is probably a dumb question, but I'm trying to understand how to properly size ujoints for a driveshaft after an axle upgrade. Should the ujoints on the front drive shaft be selected to match those on the new front axle shafts, or should they be one size smaller to allow failures to occur on the driveshaft ujoints instead of on parts that are more expensive or harder to repair in the field? I read somewhere that ujoints should be treated as the "fuse" in a driveline setup so that they would fail first. Is this correct? If the driveshaft ujoints are sized to match the front axle shaft ujoints, then would a driveline failure be more likely to cause damage to the transfer case and transmission?

    To provide context, I'm planning an axle upgrade for my 2015 JKUR, and I'm strongly considering the Dynatrac Hard Core Plus XD60/XD60 axle package with ARB lockers and 4.88 gears. I plan to run 37" tires now and 40" tires later, and the use case is rock crawling. The entire drive train is currently stock. If I understand the Dynatrac website correctly, the XD60 uses 4140 series ujoints at the steering knuckles, and I presume the same size at the pinion yoke. Should I be looking for a driveshaft with 4140 series ujoints also (do they exist?), or should I step down to the 1350 ujoints for the driveshaft? Would the sizing for the rear driveshaft in this case be the same as for the front driveshaft?

    Please go easy on me. I'm new to the forum and still in the planning stage on this build. Thanks!

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    Nothing but a Thing RESURECTIONJK's Avatar
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    UJoint Considerations for Axle Upgrade

    First off... welcome. Jump to the wave section and say hi. It will go a long ways in getting some help here. Second... the XD60 front uses a 1550 ujoint. The 4140 youre referring to is the grade of aluminum. That being said. The rear XD60 likely uses a 1410 u-joint at the yoke so, if it were me Id stick with that for the rear at both ends. Front drive shaft I would go with whatever Dynatrac recommends which is likely a 1350, could be a 1410 but I highly doubt it.

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    Addict Brute's Avatar
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    Quote Originally Posted by RESURECTIONJK View Post
    First off... welcome. Jump to the wave section and say hi. It will go a long ways in getting some help here. Second... the XD60 front uses a 1550 ujoint. The 4140 youre referring to is the grade of aluminum. That being said. The rear XD60 likely uses a 1410 u-joint at the yoke so, if it were me Id stick with that for the rear at both ends. Front drive shaft I would go with whatever Dynatrac recommends which is likely a 1350, could be a 1410 but I highly doubt it.
    I have XD60s on Brute...drive shafts are 1350s...

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    Resident Smartass OverlanderJK's Avatar
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    Quote Originally Posted by RESURECTIONJK View Post
    First off... welcome. Jump to the wave section and say hi. It will go a long ways in getting some help here. Second... the XD60 front uses a 1550 ujoint. The 4140 youre referring to is the grade of aluminum. That being said. The rear XD60 likely uses a 1410 u-joint at the yoke so, if it were me Id stick with that for the rear at both ends. Front drive shaft I would go with whatever Dynatrac recommends which is likely a 1350, could be a 1410 but I highly doubt it.
    1410 with an 80. I doubt a 1410 would even fit in the front.


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    Knows a Thing or Two rubiDave's Avatar
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    You probably wont be happy with 4.88, especially if there is a chance you'll put 40s on it. Would be between 5.13 and 5.38 if it were me.

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    Hooked Noble Woodsman's Avatar
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    Ok, so it sounds like I should use the same size ujoints on both ends of a driveshaft, and I should size them to match the ujoints on the respective axle yokes. For the XD60 front driveshaft, it sounds like they should be 1350 series. Does this approach mean the driveshaft ujoints are/should be the weak link in the driveline, or am I thinking about this incorrectly? I read on another thread here that it's easier in the field to replace a front axle shaft with a broken ujoint vs. a driveshaft with a broken ujoint, which makes sense, so maybe the driveshaft ujoints should not be the weak links?

    rubiDave

    You probably wont be happy with 4.88, especially if there is a chance you'll put 40s on it. Would be between 5.13 and 5.38 if it were me.
    Thanks for the tip, rubiDave... I've been on the fence about choosing 4.88 vs. 5.13. I forgot to mention that this will be a DD while it's still on 37s, so that was why I was leaning toward 4.88s. I run about 2500 RPM at 70 MPH with stock wheels and 4.11s currently (auto transmission). According to the Tire Size vs. RPM chart at the prodigy performance website (https://prodigyperformance.com/blog/...io-calculator/), I should expect similar RPM at 70 MPH with 37" tires. 5.13 gears with 37s would put my highway RPMs higher than they currently are, which I was hesitant about for fuel economy (I know, probably a bad argument considering it will be on 37s). Since it will be a DD when on 37s, do you still think 5.13 are the way to go?

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    Knows a Thing or Two A.J.'s Avatar
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    5.13s or 5.38s agree


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    Knows a Thing or Two rubiDave's Avatar
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    Highway RPMs are only part of it. Big heavy tires take more torque to get going. Lower gearing will improve your acceleration and need to downshift on hills, etc at the price of highway fuel economy.
    A lot of people run 4.88 with 37s and are OK with them, but 5.13 offers better performance.
    I think 4.88 would be a poor choice if you're considering 40s and I would think about 5.38 in that case. Since your getting custom axles might as well get them built for your end plan.

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    Nothing but a Thing jdofmemi's Avatar
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    Quote Originally Posted by Noble Woodsman View Post
    Ok, so it sounds like I should use the same size ujoints on both ends of a driveshaft, and I should size them to match the ujoints on the respective axle yokes. For the XD60 front driveshaft, it sounds like they should be 1350 series. Does this approach mean the driveshaft ujoints are/should be the weak link in the driveline, or am I thinking about this incorrectly? I read on another thread here that it's easier in the field to replace a front axle shaft with a broken ujoint vs. a driveshaft with a broken ujoint, which makes sense, so maybe the driveshaft ujoints should not be the weak links?

    1350 front is fine.

    Yes, the axle U joints are bigger, but there is the added gear reduction in the differential to multiply the torque before it gets to them, so they need to be stronger.

    Remember, each level of gear reduction brings a corresponding multiplication of torque, minus the friction of the gear.

    Quote Originally Posted by Noble Woodsman View Post

    Thanks for the tip, rubiDave... I've been on the fence about choosing 4.88 vs. 5.13. I forgot to mention that this will be a DD while it's still on 37s, so that was why I was leaning toward 4.88s. I run about 2500 RPM at 70 MPH with stock wheels and 4.11s currently (auto transmission). According to the Tire Size vs. RPM chart at the prodigy performance website (https://prodigyperformance.com/blog/...io-calculator/), I should expect similar RPM at 70 MPH with 37" tires. 5.13 gears with 37s would put my highway RPMs higher than they currently are, which I was hesitant about for fuel economy (I know, probably a bad argument considering it will be on 37s). Since it will be a DD when on 37s, do you still think 5.13 are the way to go?
    RPM is only part of the fuel economy calculation. You need the engine in a range to produce enough power to move you without lugging and struggling.

    With 37's, you have more rolling resistance, as well as more wind resistance. This takes more power to overcome than stock tires, so the engine needs to be where it can make that amount of power easily. That's part of why 5.13 is a better choice for 37's. They also let you get to speed easier, so it is not a drag to drive.

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    Hooked JJ151's Avatar
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    Quote Originally Posted by Noble Woodsman View Post
    Ok, so it sounds like I should use the same size ujoints on both ends of a driveshaft, and I should size them to match the ujoints on the respective axle yokes. For the XD60 front driveshaft, it sounds like they should be 1350 series. Does this approach mean the driveshaft ujoints are/should be the weak link in the driveline, or am I thinking about this incorrectly? I read on another thread here that it's easier in the field to replace a front axle shaft with a broken ujoint vs. a driveshaft with a broken ujoint, which makes sense, so maybe the driveshaft ujoints should not be the weak links?



    Thanks for the tip, rubiDave... I've been on the fence about choosing 4.88 vs. 5.13. I forgot to mention that this will be a DD while it's still on 37s, so that was why I was leaning toward 4.88s. I run about 2500 RPM at 70 MPH with stock wheels and 4.11s currently (auto transmission). According to the Tire Size vs. RPM chart at the prodigy performance website (https://prodigyperformance.com/blog/...io-calculator/), I should expect similar RPM at 70 MPH with 37" tires. 5.13 gears with 37s would put my highway RPMs higher than they currently are, which I was hesitant about for fuel economy (I know, probably a bad argument considering it will be on 37s). Since it will be a DD when on 37s, do you still think 5.13 are the way to go?
    Like you I just installed the XD60s front/rear w/37s on my 2016 JKUR and replaced my stock Rubicon axles that had 4.10 gears. I went with 1350 drive shafts, which are working fine so far. As far as gears, I too, was concerned about 5.13s on the highway and my RPMs are close to 3k at 70 on the highway. However, with the added weight I am very glad I went with 5.13s and believe I would not be happy with the performance of 4.88s.


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