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  • High Speed Vibration

    I'm a very happy new owner of a 1985 CJ7 with a high speed vibration problem. It has a 2/5 inch lift & the shims were there on the springs, but the angle between the transfer case (rear wheel) and the differential was pretty steep, so the mechanic (35 years experience working with another guy with 45 years of experience) installed the kit to drop the transfer case. Now the angle is right on, but the high speed vibration persists. It is bump induced and ranges through some harmonics as bumps are encountered. Today they took the rear drive shaft off & the vibration ceased. The U-joints have been replaced. There is a little looseness in theoutput yoke on the rear wheel drive. The only time I can count on the vibration stopping is if I come to a stop. Hitting the gas, brakes, clutch, etc., has no effect. Can anybody give me some ideas of what is next or am I going to have to sell my grandchild to pay for the repairs or shall I just wait for something to break? Any help would be greatly appreciated. Thanks, drhazel

  • #2
    O.K. help me out here. Can you explain what "they took the rear drive shaft off and the vibration ceased" means? If it's a "high speed vibration" how did you check that? Without a rear drive shaft, how did you reach high speed?

    Anyway, I'm thinking that it may be a few things. First, and the dumb question is; have you had the tires balanced lately? Second, you may need shims on either the pinion yoke or output shaft in order to tighten it up. Also, depending on the original length of the drive shaft and the amount of lift, you may need a longer drive shaft. This is a stretch though since you stated that you only had a 2/5 inch lift and have dropped the T-case, but you may want to check it out. Lastly, check that axle shafts. you may have one that's bent slightly or, better yet, you may have a wheel bearing that's not seated properly.

    That's all that I can think of, good luck and I hope this helps.


    • #3
      Hello & Thanks, Sorry for the lack of clarity. By "high speed vibration" I meant that the vibration itself is high speed. It actually starts up at as little as 10 mph and as high as 45 mph. They took the rear shaft off and drove it a ways in front wheel drive to see if the vibration might have originated elsewhere. That "2/5" lift actually was supposed to be 2.5 inches. I'll check about the balancing the send the other ideas to the mechanic. Thanks a lot for your consideration of the problem and for the help. If these changes in clarification give you some more ideas, please send them my way. Thanks drhazel


      • #4
        Check your drive shaft. If its out of balance it will be just as you decribe


        • #5
          High Speed Vibration

          I agree with the rest of them. Have you driveshaft checked and double checked. If that don't solve it check the pinion and yoke goin into the rear differential. Just thinkin that cause I own an '83 CJ-7 with 5 inches of suspension lift and 2 inches of body, and I have not had any short of vibration problems what so ever, on top of that I do not have a T case lowering kit on mine. Now you said that the rear yoke has slop...that could be bad, check you bearings and all fluid levels as well. Other than that I am clueless, like I said mine is lifted way on up there with no vibration problems, with no lowering kits. The only difference might be that I have had the rear end rotated up (instead of shims). This is simply done by cutting off the original mounts off the axles and have them rotated and rewelded.