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Bad vibrations with lift

Discussion in 'Mitsubishi Minicab' started by Nathan Marshall, May 2, 2021 at 3:22 PM.

  1. Nathan Marshall

    Nathan Marshall New Member

    How is everyone handling bigger lifts in regards to the rear shaft?

    Little back story; 1994 Mits U42t. So I built myself a lift kit, dropped all members 4 inches, made some custom struts. Ended up with about 5.5 inches lift in the front.
    Used 4 inch tapered blocks in the rear, thinking that the ujoint angles would be too much with straight ones (I now know a little more about driveline angles realize it's not just about individual u-joint angle, both joints have to match).
    Upon first drive, vibrations were bad. So I dropped the rear of the t-case about 1 inch. That calmed the vibrations while in 2wd, but in 4wd it is virtually undriveable. Assuming this is because the t-case is now pointed up at the front and the diff is still level.

    1:Has anyone used straight 4" blocks in the rear with the stock shaft? I did have some driveshaft spacers made, 1.25" I think, if memory serves.

    2:Keep the angled blocks and have a custom shaft made with double Cardon?

    3:Or could I drop the nose of the front diff so that the angles matched?

    I'm thinking the first 2 would allow me to raise the t-case back up and correct the operating angles, I'm just worried that will make too much angle for the joints as the shaft would be near 45degrees.
    The third option is alot of work I think, and still wouldn't totally fix the vibrations from the rear.
    I put alot of work into this lift and I'm really happy how it turned out but I'd really like to minimize vibrations. Hoping someone can give me some clarity here.
     
  2. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    You can drop the back of the transmission, and rotate the axle to restore the angles.
     
  3. Nathan Marshall

    Nathan Marshall New Member

    I did that. That made 2wd better. However, that makes the front shaft vibrate to the point of chattering my teeth. If I go over 30kph, I'm quite sure it will destroy something
     
  4. A. Gillingham

    A. Gillingham New Member

    Any angle over 3 degs isn’t recommended by u joint manufacturers. These angles you’re implementing here aren’t going to end well from my experience in this field and my opinion on this matter.
     
  5. Nathan Marshall

    Nathan Marshall New Member

    I appreciate your input, and I understand it's not ideal, but I'm pretty sure there is more than 3 degrees driveshaft angle from stock. I'm not talking combined angle of both joints. Not trying to argue, I'm just trying to understand what my options may be. Let's say the rear diff flange is 90deg to the floor, as is the tailshaft. Due to the short rear shaft, that makes alot of angle of the shaft. How much shaft angle will be acceptable? I'm going to measure the angles I now have tonight and I'll post them. I'm sure guys have done this high of lift in these trucks and I'm wondering how they accomplished this short of some kind of portal axle setup
     
  6. A. Gillingham

    A. Gillingham New Member

    I found some driveshaft angle geometry that I’ll share showing the causes for vibration in most cases. The shafts must be in phase as well off course. The best joint for such large angles would be off course CV joints as we know. C1AADA28-DE0D-47F6-B68D-421139D20129.jpeg C1AADA28-DE0D-47F6-B68D-421139D20129.jpeg 59292C76-FD59-4C7D-ADC8-3A090EA41B87.png
     
  7. A. Gillingham

    A. Gillingham New Member

    And off course the phasing.
     

    Attached Files:

  8. A. Gillingham

    A. Gillingham New Member

    You mentioned arguing but there’s not much sense in that imo, I’ll just try to help the best I can.
     
  9. Nathan Marshall

    Nathan Marshall New Member

    I appreciate the help, I'm pretty green here lol. I put some straight 4" blocks in and raised the t-case back to the stock location. That gave me 7deg at the tail, 8 deg at the diff and 23deg at the shaft. There is now a rear shaft vibration that was not there before.
    7 deg at front output, 2 deg at front diff, and forgot to measure the shaft angle bit it looks pretty shallow. Did not test for front shaft vibrations yet but I assume they will be less than before, but probably still there from those numbers.
    Did not check phasing, they are stock shafts

    You mention CV joints being the best for this application. There is a driveline shop nearby, i guess I will pop in there and see if they can make me something
     
  10. Nathan Marshall

    Nathan Marshall New Member

    In a CV setup, does the slip have to go in the shaft or would it be ok to leave the slip at the output?
     
  11. A. Gillingham

    A. Gillingham New Member

    The slip distance should be the same so, as long as the new shaft is showing the same position of the original shaft it should be ok imo. This is just my opinion due to not a lot of these I’ve witnessed and just using my opinion as the ride travel is stock I’m thinking.
     

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