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  1. #1
    Bill in MT
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    driveline thump

    I replaced the center bearing/mount on the driveshaft, and guibo. The old one was torn and the driveshaft thumped on hard turns, under acceleration. Now I still get the thumping, clearly coming from the center of the driveshaft against the tranny tunnel, when I accelerate hard.
    Any thoughts about why this is happening? U-joints? I did remove what I assume is a balancer on the rear of the tranny - it was torn up and somewhere I got the idea that it wasn't necessary. Could vibration there be carrying down the shaft and making it thump in the middle?
    Thanks for any help u can offer.


  2. #2
    Bubba
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    Re: driveline thump

    I had the same issue with my 1988 750, I changed out the center bearing and the transmission bushings and still the thump (from idle to about 35 MPh). I cured the thump by replacing the driveshaft (THRASH).

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    Re: driveline thump

    I'm afraid I'm having the same issue on '88 735i :-(

    The car makes horrible noises and vibrates below 35 mph or so. Happens only when the car is hot (strange) and after the brakes are applied. But since the noise and vibration are coming from the center of the car, I don't think it's brakes-related, thought I'll be replacing pads, rotors and front calipers.

    So... How do I check? How much will replacement driveshaft cost?Mike.S

  4. #4
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    could be shot U-joints

    I recently rebuild my driveshaft (repair story with pictures is in progress), replaced centerbearing and front U-joint due to the thumping noise underneath the car when taking off.

    The front U-joint was seized up and threw the center bearing (actually the rubber sleeve), a common problem. This also causes rapid wear of the tranny mounts. You should always check the play of the U-joints, move them back and forth. Stiff U-joint usually means a rebuild drive shaft (although you can replace the U-joints, but after my personal experiences I wouldn't recommend it).

    The balancer on the rear of the tranny is some sort of damper, I wouldn't remove it as the tranny mounts are way underdesigned. <b><font size=2 face="Verdana">Sean750</b></font>
    <p><font size=1 face="Verdana">BMW 750i '88 -- BMW 750iL '88 -- Porsche 928S '86
    -------------------------------------------------
    <a href="http://bmwe32.student.utwente.nl/" target="_blank"><i><font color="blue">Johan & Sean's E32 page....a technical E32 reference</i></font></a>
    <a href="http://bmwe32.student.utwente.nl/" target="_blank" class="postlink"><img src="http://bmwe32.student.utwente.nl/sean750/screendumpSite.jpg" border="0" />

  5. #5
    LJ Martin
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    Manufactures don't put parts on cars that are

    unnecessary. Put ALL the parts back on it. Should solve the problem

  6. #6
    Bubba
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    Re: driveline thump

    I bought the driveshaft for my 750 from THRASH and it cost $350 (free shipping both directions)plus a refundable core charge of $60.00.

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    Re: driveline thump

    Bubba, thanks!

    I want to make sure that I'm not replacing the wrong things here. I have not looked at it yet, but...

    - Why is it only happening when hot?
    - Why does teh noise go away at speed?
    - Why is vibration and noise directly related to the car speed and not the engine speed?

    Something tells me that it might not be the driveshaft (keeping my fingers crossed). What do you think?

    PS. Who/what is Thrash?
    PPS. I assume that a 5-speed driveshaft is different from an automatic one? ETK is a bit unclear.Mike.S

  8. #8
    Bubba
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    Re: driveline thump

    I think there is more load off idle on the drivetrain and that is why she thumps. Can not answer the hot versus cold issue. I never had an issue at speed with mine, only off idle acceleration. TRASH is thrashdriveshfts.com a TEXAS company used by many on this board. I think the maual transmission driveshfts uses a flex disc or GUIBO along with the shaft, my auto had no flex disc just two "U" joints and that is what goes on these cars.

  9. #9
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    Same problem

    I replaced the centerbearing last year and after 2 months it started thumping again. I just found out last weekend (busted tranny) that my front U-joint is seized.

    The big rubber block on the tranny is only on the 750i. It's not in the 735. Don't know about the 740i.Johan
    1987 735i

    <a href="http://bmwe32.student.utwente.nl"><img src="http://bmwe32.student.utwente.nl/images/johan_sean_e32_s.jpg"></a>

  10. #10
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    Re: driveline thump

    If a new driveshaft doesn't cure the problem, the thumping sound is likely coming from a small area of the shaft hitting the heat sheild. Even a new driveshaft will flex to some degree. Try removing the heat sheild and inspect for signs of chafing. Carefully pound out the heat sheild in the area where chafing is evident. Also check to make sure that a weld tick isn't protruding on the shaft. The tick can be ground down using a hand drill grinder.

    Since you've already replaced the center bearing, thumping during acceleration indicates the driveshaft u-joints are binding. If trying to avoid replacing the driveshaft, remove it while the heat sheild is already off and lubricate the u-joints with a quality lasting liquid lubricant. Saturate the joints and work in the lubricant by moving them back and forth for at least a few minutes. The front joint will typically be very tight but then it sees much less movement than other joints. Any of the so-called super engine treatments would be a good lubricant for this because they tend to penetrate well but aren't subject to deterioration from heat. Most penetrating liquids tend not to work as well because they're too thin and would tend to evaporate.

  11. #11
    Randy
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    Re: driveline thump

    You definitely need a new driveshaft. I have talked with several driveline companies and all told me that the worn centerbearing is a direct result of a worn out driveshaft. Replacing only the centerbearing is only a temp fix as it will soon wear out too.

    My theory on why the thump at low speed is that the driveshaft has more flex at the lower speed )aggravated by the worn centerbearing) at higher revolutions, it tends to stabilize itself. The heat is probably weakening the rubber of the centerbearing and allowing for more flex.

    That's my theory . . . coming from experiencing a worn out driveshaft.

  12. #12
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    Re: driveline thump

    Thanks!

    Out of curiocity, if only the center bearing is replaced, how long will the new one last, in miles, if the driveshaft is worn?

    Is there an easy mechanical indication of a worn driveshaft besides the noise?Mike.S

  13. #13
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    What goes into a rebuilt driveshaft?

    What do they do to an old driveshaft other then replace the CV and U joints. Is there any machining involved?
    1988 735i 210k
    1993 740i 150k
    1994 740i 155k
    wanting soon 1994 740iL/750iL (Black)

  14. #14
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    not sure but

    Although I never seen a rebuild driveshaft from BMW, I expect a rebuild driveshaft has 2 replaced U-joints (with or without a grease fitting). If it's a good rebuild job, they probably pressed the old U-joints out and machined grooves for snap-rings so the new U-joints could easily be replaced in the near future (that is how I like it).

    Furthermore a replaced centerbearing and a replaced rear CV-joint. And after that the whole unit balanced.

    I had a shop replacing my front U-joint instead of buying a rebuild driveshaft and I am not quite happy with the job they did. They removed the old U-joint with a blow torch and pressed a new one in. They didn't machine grooves and staked the new one simply with a punch.

    The problem is that the new U-joint must be perfectly aligned in the center of the driveshaft and they didn't do that perfectly. Also the driveshaft wasn't balanced after the job.<b><font size=2 face="Verdana">Sean750</b></font>
    <p><font size=1 face="Verdana">BMW 750i '88 -- BMW 750iL '88 -- Porsche 928S '86
    -------------------------------------------------
    <a href="http://bmwe32.student.utwente.nl/" target="_blank"><i><font color="blue">Johan & Sean's E32 page....a technical E32 reference</i></font></a>
    <a href="http://bmwe32.student.utwente.nl/" target="_blank" class="postlink"><img src="http://bmwe32.student.utwente.nl/sean750/screendumpSite.jpg" border="0" />

  15. #15
    Bubba
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    Re: not sure but

    Petty much everything that can be replaced is replaced to include center support bearing and then the shaft is dynamically balanced.Some companies use replaceable "U" joints and add a grease fitting on the joint (hard to get at to grease on the V12 with that exhaust system in the way). Google import drive shafts or go to thrashdriveshafts.com (only one company) and check out their rebuild procedures. Prices range from $350 to $500 and warranties from 1 Year and 12,000 miles to 5 years and 50,000 miles.

  16. #16
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    How do you "balance" the drvieshaft?

    So, should I just bite the bullet and spend a little more on having a professional else install all the parts on my driveshaft.
    1988 735i 210k
    1993 740i 150k
    1994 740i 155k
    wanting soon 1994 740iL/750iL (Black)

  17. #17
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    I tried this "quick fix" of just replacing

    the center bearing and transmission mounts, and I think I only got to drive it 2 -3 months before the thump came back with a vengeance. According to my homework, the driveshafts can be expected to last around 100,000 miles, but I have gotten approximately 250K from both my 735's. The mechanical indication is that the universal joints stiffen up. Of course, there's no way to tell unless you unbutton the bottom, which, at that point, you might as well do the whole job. I have heard that if you soak them with oil or a heavy duty lubricant, you can bring them back to life. A guy at the wrecking yard to ld me if you pound on the ears of the driveshaft where the u-joints are pressed in, it will loosen them up and keep them usable for a few more years. Finally, if you are planning on replacing the driveshaft, order your gasket for the end of the CV joint on the rear of the shaft well in advance. Here, I can only find it at the dealer and it takes them 2-10 days to special order it. Good luck-I'm doing mine this weekend.88 735i Delphin/Gray+300K mi (IR)
    90 735i Black/Gray 260K mi

  18. #18
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    How long can a revived U-joint last w lubrication?

    Patrick C 88 750 144K

  19. #19
    Bubba
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    Re: I tried this

    Good point, I banged the daylights out of the ears and then added some grease and she lasted right at two years.

  20. #20
    Bubba
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    Re: How long can a revived U-joint last w lubrication?

    Patrick, mine lasted two years and not a day longer.

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