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Thread: drive train noise FIXED with a smart phone. Seriously.

  1. #1
    Join Date
    Sep 2009
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    Colorado
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    1994 540i, 2002 330xi

    drive train noise FIXED with a smart phone. Seriously.

    TL;DR: If you plan to work on your driveshaft or if you developed noise after doing so, please do read on. I think this could could really help you!

    Back in June I finished putting a new-to-me engine/tranny in my 2002 330xi. (search this forum for "pig fat")

    Afterwards, there was a definite (not okay!) vibration in the drive shaft around 30 MPH. I did a lot of searching on the web, and one (and only one) thread I found mentioned the issue of driveshaft alignment. Bentley, of course, mentions this but who reads books any more?

    The idea is that if you imagine a laser beam pointing out of the tranmission (or transfer case) along the axis of the output shaft, that line should point directly along the center of the input shaft of the rear diff. This line should be be centered on the chassis, and the entire drive shaft should be perfectly centered along this line.

    Bentley desribes two specific checks that should be made while installing the drive shaft.

    1) Side to side alignment.

    I checked, and in fact my drive shaft was not centered at the front end. I LOOSENED (did not remove) the 4 bolts that hold the aluminum tranny carrier to the chassis (mine is a manual, 4WD), the one bolt that goes through the rubber tranny mount, the two nuts on the two engine mounts, and two nuts on the center support bearing (CSB). I also used a floor jack and a piece of wood to lift the engine up a bit.

    Then I sort of pried, hammered, shoved and wiggled stuff until a precise measurement gave me "2 and 15" on either side of the driveshaft; i.e., two fingers plus the thickness of a 15 mm spanner I had nearby. The point is, the space on either side should be equal. Then, in order, I tightened: CSB (with preload), tranny carrier, tranny mount, and finally engine mounts.

    2) Vertical alignment.

    Granted, this one is less likely to be affected by (proper) work on your car, but it turned out this was the source of my problem. Bentley is very vague about *how* to test this, but the point is that the front and rear halves of the drive shaft need to be at exactly the same vertical angle.

    My plan was to go into work where my machinist friend has a very cool inclinometer with a magnetic base. When I got there, I snooped around but couldn't find it. Then it dawned on me:

    EVERY SMART PHONE HAS AN INCLINOMETER BUILT IN!

    (That's how it knows which way to rotate your screen.)

    So I downloaded an app that displays this angle. There are tons of them, I picked one called "Inclinometer." It displayed the angle of the phone in increments of 1 degree. I figured this would be good enough.

    I crawled back under the car and gave it a go. The difference in angles between the front and rear halves : a shocking 8 degrees! Ain't no shim gonna fix that.

    Then it dawned on me. I did read a thread about somebody who said they put their CSB in "upside down." Now, I would never, ever do that: I would never say "upside down" when I really meant "backwards." Because, obviously, you just *can't* put a CSB in upside down. I ignored that thread b/c it didn't even make any sense.

    Well, my friends, I now know that you really can put a CSB in upside down. Fortunately, as I discovered, you can remove the two nuts and lower it enough to (just barely) rotate it by 180 degrees around the drive shaft and put it in the right way.

    After that, I whipped out my phone again and found the two halves of the drive shaft to be at exactly the same angle.

    WOW!

    The drive shaft noise is completely gone. The car drives smooth as silk now. I have babied it up until now, but tonight I did one really hard acceleration (0-40 MPH) and think I even chirped the wheels in second gear. (Front wheels? Back wheels? All 4? Who knows.) Anyway, it was awesome. For me, anyways. The person in the car further ahead pulled way, way over to let the jerk in the BMW go by. Oops.

    Anyways, hope this helps.

  2. #2
    Join Date
    Nov 2018
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    La Habra, CA
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    2002 525i
    The "round part" of the CSB goes against the floor pan, sometimes with a strip of butyl to help dampen vibration. Are you saying that you accidentally installed the CSB with the "round part" pointing down toward the ground?
    Current stable:
    2002 525i (Daily Driver)
    1994 SN95 Mustang 'Vert (The Bumblebee)
    2001 325i Convertible (Beach cruiser project)

  3. #3
    Join Date
    Sep 2009
    Location
    Colorado
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    1994 540i, 2002 330xi
    Quote Originally Posted by E39 Newbie View Post
    The "round part" of the CSB goes against the floor pan, sometimes with a strip of butyl to help dampen vibration. Are you saying that you accidentally installed the CSB with the "round part" pointing down toward the ground?

    Wow, I just looked at a picture of a CSB and it really, really looks like it can only go one way. That's probably why I ignored the post about making sure not to put it in upside down. Even if it was physically possible, only a complete idiot would do that.

    Oh, and the answer to your question is "yes".

  4. #4
    Join Date
    Nov 2018
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    La Habra, CA
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    2002 525i
    Quote Originally Posted by js22 View Post
    Wow, I just looked at a picture of a CSB and it really, really looks like it can only go one way. That's probably why I ignored the post about making sure not to put it in upside down. Even if it was physically possible, only a complete idiot would do that.

    Oh, and the answer to your question is "yes".
    Thanks. I was just making sure I understood. Glad you figured it out.

    Recently I had a ton of drivetrain vibration. And occasionally, if you were driving slow with the windows down, I'd hear a squeak kind of like what a worn-out U-joint sounds like. So, I tore off the exhaust and heat shield and, lo and behold, the driveshaft and CSB were pristine. Ugh.

    Turns out a wheel was seriously bent. D'oh! And the occasional squeak was just a flaky brake caliper probably not fully releasing. Sigh. They're next on the hit list.
    Current stable:
    2002 525i (Daily Driver)
    1994 SN95 Mustang 'Vert (The Bumblebee)
    2001 325i Convertible (Beach cruiser project)

  5. #5
    Join Date
    Dec 2008
    Location
    Washington, NC
    Posts
    1,098
    My Cars
    01 330 CiC, 05 X3 3.0
    Nice! I used a vibration analysis app on my phone to pinpoint the vibration in my e46 to the diff based on vibration frequency vs rpm.

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