Drive Shaft Vibrations

    Goodmorning 8ers!

    i come to you with today's 8 riddle! one that i have been trying to solve for 2 months with no solution in sight! please help!:help:

    my 850 has been vibrating in the drive shaft area (felt between the front seats) for over a year now.
    at first it was not being used; but due to a recent reallocation i have been using it as a daily driver for the past 3 months; hence the urgency to fix it.

    At first a "kicking sound" form the drive shaft was being heard every time i pressed on the gas abruptly; this kicking could be avoided if you started of the car slowly.

    After showing it to the mechanic we changed the central bearing (26 12 1 226 662), the universal joint (26 11 1 229 583), the engine rubber mounts and gear rubber mounts.
    This then gave place to a new much softer (and much less scary) vibration between 30 and 60 kms/hr.
    These new vibrations cannot be avoided in any case whether i press on the gas fully or gradually.:banghead:


    this then gave the need to change the Constant-velocity joint with knurled bush (26 11 1 229 099) and the rubber mounting rods (31 12 1 136 607). BUT, the vibrations are still there!:banghead::banghead: and as if the new changes did not affect the car at all! :dontknow:
    i say this because every time we changed a part; I was there and every part we changed really looked destroyed and needed to be replaced.

    we made a few test drives and noted that the vibrations occur everytime we put pressure on the drive shaft; however it is felt much less at higher speeds (practically not felt at higher speeds)

    in these test drives we also checked if it was a gear problem; but it isn’t. we tried starting the car at different gears with the steptronic gearbox, and the car shows the same vibrations at any gear.:top:

    so at the moment i am starting to lose trust in my mechanic’s abilities; and i don’t want to use a trial-and-error approach in fixing the car.. i would really appreciate all of your combined expertise in order to make another thought of and educated move to fix these extremely annoying vibrations; any input would be extremely appreciated guys!

    Thanks alot!

    Feras

    Drive shaft is balanced just like any wheel.
    Minor imbalances are indeed common (at least I know of them in quite a few cars) and appear exactly as you describe upon acceleration from standstill and vanish above 60kph.


    If taking apart the drive shaft one MUST reassemble it in exactly the same positions as before or have it rebalanced. Since I am certain that the drive shafts in all my cars have never been removed but still have that vibration, I feel safe to assume that it is not a bug but rather a feature :D


    If you find a place where you live able to rebalance the drive shaft then this is what I´d lean towards.


    Cheers
    Reinhard

    Hey guys,
    I havent balanced the driveshaft yet but i have new observations:


    The vibrations only occur when i push the car. This means that if i start off slowly, or press on the gas peddle lightly, the vibrations are nearly not there.
    Addtionally, when i drive ar high speeds and let go of the throttle for a while, when i press on the gas again the car jerks and doesnt pick up smoothly..


    Any thoughts? Ideas? Every input is welcome.. I live in a place where 8s are very rare and the mechanical knowhow for this car is even rarer!

    Both of my 840ci's have had vibration under harsh acceleration which tails off as the road speed increases. So did the 840ci's I test drove when looking for my first one. I managed to reduce this 'feature' by replacing the gearbox mounts:


    http://www.meeknet.co.uk/e31/E…on_Mounts_Replacement.htm

    You might also check the bearing on the rear differential. If this is worn, things may go out of alignment when under torque ("press on the gas").

    I think it's not much more work to what you've already done, to change the differential bearing and its seal.

    Given the ratios, you should quite easily be able to feel if it is vibrating at propshaft frequency or driveshaft (wheel) frequency. That will narrow it down.

    My 840 had a vibration under part load which was too fast to be wheel/drive shaft. I suspected the prop or gearbox mounts.
    Luckily, the previous owner had bought an expensive BMW warranty, so I took it to a main agent to sort.

    After a week of head scratching and calling around they found someone who had come across a similar problem and found a fix.
    They removed the small access cover and added washers to some of the bolts around the flywheel - problem solved.
    Strange fix, but that was six years ago and all still remains smooth!

    My 850 has the same shaking, but only when it's cold. Could it be the same culprit?

    Current Cars:
    1994 BMW 850 CiA (204k km). My black on black chipped 5.0 liter V12 autobahnmuncher
    1992 Donkervoort S8AT (101k km). The mad dutch "Super 7." 300hp/ton of turbo power
    2013 VW Caravelle 4Motion (26k km). A dark wine red 180PS/400Nm 2.0 BiTDI rocketvan


    "The best way to go broke-by-german-car is to buy an 8 series bmw with a v12" - Perc
    "Torque is like porn. You can't really define it, but you will recognize it." - ElToro

    Thanks alot guys! i will make sure to keep the balancing and the prop shaft seal in mind.


    Saturday ill go to the mechanic and ill report right back with a report.


    we should create a Giant Troubleshooting manual that combines all the experiences of fixing various problems and filtering them down. Plus we could add a did you know section relevant to each part of the car where people can place their tips and tricks or even things to remember checking or replacing on a special problem.


    Who is in??

    1. Check if rear wheels are balanced. Unbalanced rear wheels make the entire car shake and it feels quite different from out of balance front wheels.
    2. Check diff. mounts. The two rubber bushings in the cover as well as the single rear one.
    3. What about all the rear axle bearings and bushings? My car had some indefinite vibration until I did the entire rear axle. No vibes at all anymore.

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