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Thread: Chasing Front D/S Vibration Demons

  1. #1
    Nothing but a Thing JK_Dave's Avatar
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    Angry Chasing Front D/S Vibration Demons

    I'll start with my current specs and then describe the problem I have.

    Current specs:

    '13 JKU lifted ~3.5"
    Front Reel 1350 Double Cardan drive shaft
    Front upper and lower control arms
    Upgraded from 3.73 to 4.88 R&P gears
    +4.4 deg caster on stock Rubicon D44 axle
    2.5 deg angle measured from pinion yoke U joint when perpendicular to the ground
    8 deg angle of driveshaft measured from the middle of the D/S body
    Stock 32" tires

    Double_Cardan_driveshaft.jpg

    The problem:

    Prior to my gear upgrade, all the specs above were the same and I had no vibration, even at highway speeds. Now, after the gear upgrade, I've got a mild vibration starting around 50mph and gets more noticeable at highway speeds. I have not had the D/S balanced because it's only been on the Jeep for 6 months and was brand new.

    I called up Reel to get their thoughts and he agreed it sounded like I needed to adjust the angle, but couldn't tell me with any certainty how much. In fact, his suggestion was to talk to Mel or Drew since they install these all the time and seem to have success with them. Before I do that, I wanted to get some thoughts from others who are familiar with this.

    My thought is that I need to attempt to straighten the angle between the shaft and the pinion yoke as much as possible, but I don't think I can add that much negative caster without encountering steering problems. Short of getting under there and adjusting the arms, test driving it and making further adjustments, can anyone give me their experience of a happy window I can shoot for? Does it sound like I'm taking the right approach here?

  2. #2
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    Is the vibration constant or more of a whir-whir-whir?

  3. #3
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    After not paying attention to the details I have removed my post to not confuse the issue.
    Last edited by branman; 12-01-2014 at 11:43 PM.

  4. #4
    Knows a Thing or Two seanb123's Avatar
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    Get bigger tires see if that helps 😉

  5. #5
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    Edited to remove my reply with quote on branman's post per his request. (to keep the topic more clean)
    Last edited by jnabird333; 12-01-2014 at 11:46 PM.

  6. #6
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    Rebalance the shaft. Fronts not under load and shouldn't vibrate with stockish caster numbers.
    You can try running 3/3 but handling with suffer.

  7. #7
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    The reason I asked about the type of vibration is I focus on "what changed".

    The OP stated they the vibration wasn't an issue until after a gear change. To me, this points to a possible poor gear set up. It is possible that the mesh it too tight and causing vibration that resonates though the DS or perhaps something is loose.

    Gear vibes are usually more constistant. while DS vibs usually resonate with variation. "whir-whir-whir". I know this isn't always the case but it's what I've seen. There are a buch of guys doing gear swaps out there that have no idea what they are doing!

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    Lower gearing = higher RPMS. If the shafts going to vibrate. It's going to happen with deeper gears. I see it a lot with folks running higher lifts, a double carden shaft and stock housing. Huge benefit with a Prorock is added caster/pinion angles.

  9. #9
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    Quote Originally Posted by 2007blackJk View Post
    Lower gearing = higher RPMS. If the shafts going to vibrate. It's going to happen with deeper gears. I see it a lot with folks running higher lifts, a double carden shaft and stock housing. Huge benefit with a Prorock is added caster/pinion angles.
    Good point!

  10. #10
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    Quote Originally Posted by jnabird333 View Post
    The reason I asked about the type of vibration is I focus on "what changed".

    The OP stated they the vibration wasn't an issue until after a gear change. To me, this points to a possible poor gear set up. It is possible that the mesh it too tight and causing vibration that resonates though the DS or perhaps something is loose.

    Gear vibes are usually more constistant. while DS vibs usually resonate with variation. "whir-whir-whir". I know this isn't always the case but it's what I've seen. There are a buch of guys doing gear swaps out there that have no idea what they are doing!
    I do agree. Of coarse it's possible.

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