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Weird vibration at 90-100 mph - doesn't exist with extra weight?!

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    #1

    Weird vibration at 90-100 mph - doesn't exist with extra weight?!

    So, I've been meaning to post this, but school has had me busy OUT OF THE ASS like crazy. It's amazing how busy school has kept me.

    Before I drove the 950 miles to school in August, I went on a couple test drives (drove to Pendleton, OR). I noticed then that when I passed speeds of $90 mph, I got a pretty substancial vibration from the rear of the car. Nothing shaking your jaw, but it sure shakes your butt a lot. I noticed driving home it was the same way.

    On my way out to school, my car was loaded down. I actually added 10mm spring pads to both sides so I could support the extra weight without tucking massively. Well, the way out - I got NO vibrations. it was like it was before - solid as a rock and not a BIT of vibration AT ALL!

    I thought - cool, maybe the pads got the car raised to the point where it was when it was aligned over a year ago.

    I recently went for another drive, passing 90 mph - and sure enough the vibration has returned.

    So, I'm thinking this. I had to change my subframe this summer since my other one cracked due to bolts falling out of my diff. Well, I figured since I didn't touch my trailing arm bushings that my alignment would remain identical - was I wrong? Did my alignment get tweaked?

    I was going to get one before I left for school - but the oh-so-awesome dealer in Boise said they couldn't get my in until AFTER I had to leave. I couldn't seem to get across to the guy that I had to get in BEFORE a certain date. Fucking idiot.

    Anyway, just wondering if what I'm thinking is right. If it is the alignment, does that explain why it didn't vibrate with the car loaded down?

    That is all! I know it's long, but I like being thorough. :)
    - Sean Hayes
    Tags: None
    #2
    the rear is not adjustable in the e30. You can only adjust toe in on the front wheels.

    Comment

      #3
      Originally posted by netcsk View Post
      the rear is not adjustable in the e30. You can only adjust toe in on the front wheels.
      Wrong.

      It is adjustable.

      How else did the dealership dial out my -5 camber to -2.5 when I got my car aligned initially.
      - Sean Hayes

      Comment

        #4
        Originally posted by Sean View Post
        Wrong.

        It is adjustable.

        How else did the dealership dial out my -5 camber to -2.5 when I got my car aligned initially.
        Sorry Sean, he is correct. There is no adjustability anywhere in the rear of an E30. If the stealership told you that, give me their name and number...I wanna talk to that tech.

        Luke

        Closing SOON!
        "LAST CHANCE FOR G.A.S." DEAL IS ON NOW

        Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

        Thanks for 10 years of fun!

        Comment

          #5
          Originally posted by StereoInstaller1 View Post
          Sorry Sean, he is correct. There is no adjustability anywhere in the rear of an E30. If the stealership told you that, give me their name and number...I wanna talk to that tech.

          Luke
          Ok - I guess I wasn't clear.

          Yea, you're not supposed to be able to adjust - and I was under that assumption too.

          However - they managed to. I specifically SAW the difference with my own two eyes. The problem with the rear is to dial out camber creates more rear toe in (I think) they can't be adjusted individually. I was SHOCKED when I got the sheet back to see they had dialed out my rear camber. I asked how they did, and the guy couldn't tell me. I didn't wanna stick around to ask the tech, so I left. But, I remember reading somewhere that the bushings can be pushed to different positions in the trailing arm - which mine were.

          But, it was indeed adjusted. My camber was BAD - but wasn't as bad when it left the dealer.



          For the sake of this arguement, lets assume it isn't adjustable.

          What would cause my rear end to vibrate with no load, and NOT vibrate with an extra 300 lbs in the car?



          Oh, and netcsk, didn't mean to sound like I was attacking you. I shoulda been more humble with my response, so I apologize. :)
          - Sean Hayes

          Comment

            #6
            Originally posted by Sean View Post
            What would cause my rear end to vibrate with no load, and NOT vibrate with an extra 300 lbs in the car?
            Could be an out of balance or bent wheel in the rear, or one/both of your rear wheel bearings are bad.

            Comment

              #7
              Originally posted by Eurospeed View Post
              Could be an out of balance or bent wheel in the rear, or one/both of your rear wheel bearings are bad.
              Wheels are not bent.

              I also had all my wheels rebalanced, and they were perfect.

              It was fine when I drove home - then when I finsihed my rebuild, it vibrated.

              Only thing changed was the rear subframe BAR was changed out - everything else left the same.

              I was thinking rear bearing too - any good way to test this? There's no noise from my car.
              - Sean Hayes

              Comment

                #8
                Wow, Sean...sounds like time for you to get a fat GF...or a mother in law.

                I have a driveshaft sitting around that has aU-joint that sticks on a certain spot. Smooth and flexible all through its rotation, except at a certain spot. I would ecpect it is worn at that spot...you can feel an indent(sp?).

                Seems to me that the angle would change when you add 300Lb to the trunk, thus getting past that indent...so it just might be a bad U joint.

                Pure conjecture on my part, but you gotta look at something, right?

                Luke
                still wondering about that camber!

                Closing SOON!
                "LAST CHANCE FOR G.A.S." DEAL IS ON NOW

                Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

                Thanks for 10 years of fun!

                Comment

                  #9
                  Originally posted by StereoInstaller1 View Post
                  Wow, Sean...sounds like time for you to get a fat GF...or a mother in law.

                  I have a driveshaft sitting around that has aU-joint that sticks on a certain spot. Smooth and flexible all through its rotation, except at a certain spot. I would ecpect it is worn at that spot...you can feel an indent(sp?).

                  Seems to me that the angle would change when you add 300Lb to the trunk, thus getting past that indent...so it just might be a bad U joint.

                  Pure conjecture on my part, but you gotta look at something, right?

                  Luke
                  still wondering about that camber!
                  LOL thanks, Luke. :p

                  Yea, I'm really at a loss of what would cause it. I don't think the car being lower in the rear affects the driveshaft. Now...it COULD be the half-shafts. For all I know, they are original, and at 230,000 miles, that's pretty old.

                  Other than rear wheel bearings, rear alignment (although not ENTIRELY adjustable), and the half-shafts, I'm not sure what else to check in the rear.
                  - Sean Hayes

                  Comment

                    #10
                    U joints in driveshaft sounds like a good guess if the wheels arent bent and are balanced correctly.

                    Will
                    RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
                    Welcome e30 (brilliantrot '90 325is) 12/23/06
                    DaveCN = Old Man
                    My signature picture was taken by ME! Not by anyone else!



                    Originally posted by george graves
                    If people keep quoting me in their sig, I'm going to burn this motherfucker down.

                    Comment

                      #11
                      Could be....

                      There is a secondary inbalance in wheels that occurs about 85-90 mph and again at 125 mph. Swap tires front to rear.
                      The rear camber may have been changed by installing BMW offset trailing arm bushings.
                      The vibration being sensitive to ride height sort of makes you think of half shafts. With a solid mounted differential there is minimal movent of the driveshaft. Also pinion and drive flange bearings (230,000 miles)
                      You could just not drive 90 mph on public highways, especially since you have a vibration. That is unless you have a death wish.

                      Comment

                        #12
                        Good luck getting me to go under 90 mph in the middle of Wyoming...yea, no. lol

                        Secondary imbalance? Tell me more. I've been meaning to switch the front and rears - although I coulda sworn I did that when I put them on after thier re-balance I had done about a month ago.

                        The trailing arms were not touched when I changed my subframe this summer. They are IE Urethane bushings - and I know they're not rubber. They did somehting to the rear. And, from the looks of it, the urethane bushings CAN move back and forth slightly, and they are nice and tight in their current position.

                        Yea, the driveshaft won't be affected at all by ride-height, so I don't think it's that. It could be my differential, but I don't see that being affected all that much by ride height.
                        - Sean Hayes

                        Comment

                          #13
                          The alignment is irrelevant because that rarely causes a vibration, so chuck that out. Personally i have had vibrations that come and go at certain speeds but not that vary under load.

                          Comment

                            #14
                            Originally posted by Sean View Post
                            Yea, the driveshaft won't be affected at all by ride-height, so I don't think it's that. It could be my differential, but I don't see that being affected all that much by ride height.
                            You are correct because the diff is stationary and does not move up and down with the suspension.

                            I would check wheel bearings. Here's how:

                            Jack the back of the car up so the wheels are off the ground. Take the parking break off and take the car out of gear. Spin the wheel as fast as you can by hand. It should spin smooth with near no noise. If there is any grinding noise or the wheel seems to "wobble" in any direction, it's a wheel bearing. You can also grab each side of the wheel and push and pull alternately on each side to see if there is any play. There shouldn't be any.

                            Comment

                              #15
                              Just to add to that, bad wheel bearings sometimes create excessive amounts of heat. After one of those 90mph drives, feel the wheels around the hub. A hot one would indicate a problem. I had a front hub bearing go bad and it was glaringly obvious to the touch.

                              But....... the vibration was constant at any speed.
                              sigpic

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