How do i "Lower" the rear end?

Discussion in 'Lift Kit Discussion' started by SAString, Jul 26, 2019.

  1. SAString

    SAString Full Access Member

    Messages:
    85
    Likes Received:
    1
    Joined:
    Dec 27, 2017
    Location:
    Overland Park, Kansas
    My KJ has an OME spring lift with Bilsteins and rides beautifully. But the rear is strangely about 1 1/2" higher than than the front. I suspect I'm getting some pinion-angle vibrations, due to the new rear drive shaft angle. I've added and maxed a JBA link (with little improvement) and using accelerometer data, I've been able to pinpoint the vibration to the rear shaft, which is 100% new (U-joints also) and precisely balanced.

    At 47MPH the 245/70/R16 tires make about 9 revolutions per second, with a 3.73 Axle ratio the shaft turns almost 34 times/second. My plot shows 34 peaks per second! Adding/clocking weights to the shaft has little effect. So narrowing in on pinion-angle vibrations.

    There are several unattractive ways to lower the rear end 1 1/2" and reduce the shaft angle:
    1. Add 475 lbs of sand bags to the rear
    2. Buy and replace the rear springs with shorter stock springs
    3. Buy some kind of "spring compressors" to permanently install
    4. Cut the springs shorter
    5. Add a clevis lift to the front (It's already hard to climb into).
    5. Heat the springs to red-hot and compress
    6. Complain to the place that installed the springs that they made the Jeep vibrate
    7. Buy a large Boat and tow it everywhere, just to reduce vibrations :)

    Anyone have any good ideas or experienced this before?
    Thanks in advance.
     
  2. turblediesel

    turblediesel memberable

    Messages:
    2,386
    Likes Received:
    184
    Joined:
    May 31, 2015
    Location:
    Isolation Alaska
    #7
     
  3. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

    Messages:
    7,162
    Likes Received:
    416
    Joined:
    Oct 24, 2008
    Location:
    B.C. Canada
    Do you have two rear top spring insulators? Could remove one each side.
    I found that the 948's will take a bit of time to settle in, as a matter of fact mine settled in too much and then sagged in the rear.
    I went to an even taller shock with the Monroe coil overs #58649 and got a nice rake happening, no sagging on my Jeep, yet I have no driveline vibration at all.
    I wonder if something else is going on, like have you checked wheel balance on a digital tire balance machine?
    [​IMG]
    Got lift? ha ha..:)
    Try throwing some good weight in the rear and see if that helps..??
     
    SAString likes this.
  4. SAString

    SAString Full Access Member

    Messages:
    85
    Likes Received:
    1
    Joined:
    Dec 27, 2017
    Location:
    Overland Park, Kansas
    Thanks. I don't see any additional isolators to remove. Tires balanced. I previously got the opportunity for the weight trick helping a friend with a load of cinder blocks and bags of concrete. Vibes reduced and I liked the stance better, rather than the rear way up in the air. Unfortunately they didn't take a permanent set and bounced right back ! Those springs are well made!
     
  5. tommudd

    tommudd Moderator Staff Member Moderator

    Messages:
    17,855
    Likes Received:
    450
    Joined:
    Jul 14, 2005
    Location:
    Southeastern Ohio
    To start with , tell us what all you did, what you added, which OME springs did you use, etc
    Did you add anything like extra iso's to the rear, also measure from middle of the wheel to bottom of the flare and report back.
    Never seen one with that much difference, but then 98% of the lifts we did here at my place we used 927 front/ 948 rear and everyone one of them sat flat level.

    Also no reason at all you should have to use the tri link extender on such a low lift

    1-7 are all very bad ideas............., sorry but would never do any of them

    I would lift the front to match the rear if I was you and running that spring setup ( shame you didn't go 927/948s )

    Also by using the lower rated springs it is going to sit with the stock rake , only 927s are going to change that
     
    Last edited: Jul 28, 2019