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Can an MML eliminate the need for a SYE?

Discussion in 'TJ General Discussion' started by JMT, Nov 13, 2017 at 9:45 AM.

  1. Fouledplugs

    Fouledplugs TJ Enthusiast

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    Also going the route of the super short SYE (I am a big JB conversions fan) can be an added advantage. A super short SYE is arguably better in the sense that it allows a longer rear driveshaft thus lowering the chances of a rear driveshaft vibration.

    Install a SYE and DC driveshaft on the TJ the first time and go from there, should spend less money that way as well.

    There is a reason the Jeep engineers tasked New Venture with building a fixed yoke output shaft on the TJ Rubicon.
     
  2. bobthetj03

    bobthetj03 TJ Addict
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    Have you ever experienced a rig that developed drivetrain vibrations after having a re-gear done, with nothing else being changed on the jeep sans replacing a right rear axle bearing because the seal was leaking a tad?
     
  3. mrblaine

    mrblaine TJ Guru
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    Yep, all the time. We have always fixed the problem by getting the driveshaft rebalanced to a higher speed if it has been on there awhile. That and the vast majority of the time, they vibrate because they are spinning at a higher speed than before and not everyone does a high speed balance.

    I've also dealt with some rigs that the rear pinion angle was sensitive to a half degree. I've set many by just looking at the yokes, making sure that the pinion is ever so slightly lower than the one on the drive shaft and we rarely have to readjust them.
     
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  4. bobthetj03

    bobthetj03 TJ Addict
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    Am I measuring the pinion angle correctly here? Second pic is the angle finder on the rear diff flats.
    20170707_082731.jpg
    20170707_082809.jpg
     
  5. mrblaine

    mrblaine TJ Guru
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    Probably but what the angle finder says doesn't matter if you still have vibes. The only thing that matters is that you change it until the vibes go away and no measurement will do that for you. Which is why we have only used an angle finder a very small number of times to set the rear pinion angle or the front one for that matter. When I say small, I mean only a couple of times over the years.
     
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  6. bobthetj03

    bobthetj03 TJ Addict
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    The pinion is sitting 0.5* lower than the driveshaft now. I have tried adjusting the pinion angle in 0.5* increments starting at completely parallel with the driveshaft to +2* up and -2* down from parallel( in 0.5* increments, then going for a test drive each time) with no change in the vibes ferocity, so either I haven't gone enough either way, or I have a problem somewhere else. Next up, I may need to take the rear shaft to a driveline shop and see if they can balance it better. For a jeep with only a 2.5" lift and 33's, I shouldn't be having these problems.
     
  7. mrblaine

    mrblaine TJ Guru
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    Put it on stands and run it to see if it has any run out. After that, set it very slightly low and drive it. If it still has vibes, get it balanced.
     
  8. bobthetj03

    bobthetj03 TJ Addict
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    That will be next on the list. Thanks.
     
  9. bobthetj03

    bobthetj03 TJ Addict
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    @mrblaine , I measured runout tonight. I measured the rear diff yoke, TC rear output yoke and rear drive shaft. Both yokes measured out around .006-.007. The rear drive shaft, .020-.022. For comparison, I measured the front driveshaft at .010-.012. Sorry to derail your thread @JMT .
    20171117_163016.jpg
    20171117_163902.jpg
    20171117_164749.jpg
     
  10. mrblaine

    mrblaine TJ Guru
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    If you run it in gear, can you see the driveshaft wobble?
     
  11. bobthetj03

    bobthetj03 TJ Addict
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    No. I put it in 4th gear and let it spin at idle(was by myself, so no helper on the throttle). Seemed to be smooth to my eyes. I even left the runout gauge attached as seen in my second picture and adjusted the tip so that is was almost touching the shaft tube and put it in 4th gear to see if the needle bounced around. It did not. What is acceptable run out on a rear driveshaft?
     
  12. bobthetj03

    bobthetj03 TJ Addict
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    Also to note, while on the jack stands, I hoped in and took it up to speed to 65mph in 2wd. No vibes. Then 4hi at 65mph. No vibes.
     
  13. bobthetj03

    bobthetj03 TJ Addict
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    To rule out wheels and tires, I swapped them with another jeep buddy's set of birddog wheels and fresh KO2's in the metric 33 size. No change in vibes other than the KO2's being a bunch quieter than my KM2's.
     
  14. Luke

    Luke TJ Enthusiast

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    I have stock coil springs, no suspension lift at all. I put in an undercover fabworks "original" high clearance skid which moved up the transmission .75" and gave me an extra 1.5" of clearance. I had a noticeable drivetrain vibration so I added in a 1" MML from JKS and there's no drivetrain vibration anymore. It's butter smooth at all speeds.


    Sent from my iPhone using Tapatalk
     
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  15. Paul Schuepp

    Paul Schuepp Crawls like a Goat with 4.88s
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    Guys, friends, an SYE is so amazing to smooth out your vibes on a higher lift, in my case 3.5". Tummy tuck then was easy.
    Tom Woods personally will give you excellent advice and instruction and sell you the SYE and crank shaft. Peace of mind.
     
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