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Thread: Let off the throttle and hear a clunk.

  1. #1
    Join Date
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    1991 BMW 850i

    Let off the throttle and hear a clunk.

    Let me start off by stating I have a 91 850i automatic. When cruising at a constant speed (mostly around 30mph) when I let off the throttle I here a clunk in the rear end and then the entire vehicle kind of lurches back and forth like I am dragging a trailer. I know I need to replace many of my suspension bushings, both in the front and rear, but is that my problem. I have not yet checked transmission mounts or anything, just looking at getting some input from some real BMW guys.1

  2. #2
    Join Date
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    You are driving a very Exotic Automobile with a high powered V12 Engine... The simple solution to your problem is to keep it floored and NEVER let off the throttle!...

    See how easy these 850s are to fix...

    That being said my 1991 850i does the same thing... I figured it was either Motor mounts, Trans mounts or the drive shaft U-Joint , Center Support etc???...

    Experts??
    Last edited by execmalibu; 01-11-2015 at 04:49 PM.

  3. #3
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    Mine too (also 91 850i). I also have a bit of a clunk when putting the car into gear (particularly reverse). Since I've done the trans and motor mounts I figured diff mount (though it didn't look bad when I swapped out the open diff for LSD) or I didn't do one of the other mounts up correctly!

    Or maybe it's just a 91 850i thing.

    Also more noticeable after installing Wokke's EML chip - so may be dirty throttle bodies
    Last edited by jeffbebe; 01-11-2015 at 04:56 PM.

  4. #4
    Join Date
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    '93 850Ci- Daily Driver
    Rear differential mounting bushings are shot
    '93 850Ci - Mineralweiss Metallic
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  5. #5
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    Anyway to be sure? Presumably lift it up, grab a stethoscope while a mate sits in the car and puts it in and out of gear and listen to which mount/s the clunk is coming from.

    EDIT: #22 below, right? (x2)

    Last edited by jeffbebe; 01-11-2015 at 08:43 PM.

  6. #6
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    it may also be that #15 might have something to do with it. Have seen those shot, have also seen them loose...
    Does the clunk happen when the car is staitionary? If you only experience that noise at speed, then I would have a look at rear suspension bushings. The lower wishbone can cause a lot of clunking and a "loose" driving experience,
    '93 850Ci - Mineralweiss Metallic
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    BMWCCA E31 Chapter President



    ...the price of cool ain't cheap!

  7. #7
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    The worst clunk is shifting into reverse from park on a slope but there is a slight 'bump' when you throttle on/off at any speed (which I had previously thought might be dirty throttle bodies).

  8. #8
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    DK's don't clunk, Has to be a bad bushing or more than one.

  9. #9
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    I didn't think the DK was causing the clunk when shifting, as mentioned above, but thought it could be responsible for the very black and white throttle response - she either goes or there's nothing and the transfer between nothing and power leads to a bump you can feel in the car

  10. #10
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    Quote Originally Posted by jeffbebe View Post
    The worst clunk is shifting into reverse from park on a slope but there is a slight 'bump' when you throttle on/off at any speed (which I had previously thought might be dirty throttle bodies).
    That is differential related. Have you checked transmission mounts? Park to reverse clunk is highly probable to be transmission mounts. I would also check engine mounts while you are at it.
    '93 850Ci - Mineralweiss Metallic
    ALPINA B7 -Alpinweiss III

    BMWCCA E31 Chapter President



    ...the price of cool ain't cheap!

  11. #11
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    As I said above, trans mounts are new and I replaced one worn engine mount but the other looked fine so I left it... Perhaps it's not fine after all (they're not hydraulic though as far as I can tell). Didn't notice the diff mounts being worn but they are pressed into the back of the case so that's quite possible.

    Will try and get under a car with a stethoscope and find out exactly where the clunk is coming from.

    EDIT: I used the back cover from my original diff when I fitted the 3.64 E34 LSD so it has the same mounts... Would explain why the throttle issue didn't go away!!
    Last edited by jeffbebe; 01-11-2015 at 10:02 PM.

  12. #12
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    Also check driveshaft u-joints and center bearing.
    91 850 (Panzer), 2012 Mini Cooper Countryman (WifeMobile) www.wuffer.ca


  13. #13
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    Thanks

  14. #14
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    Sounds like diff mounts are blown & the diff. Is binding due to excessive lash & case articulation.

  15. #15
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    I would also replace the other engine mount, they tend to settle as they degrade and lose height. Transmission mounts too

    Hope this helps
    Regards,

    Brian
    Cave Creek, AZ

  16. #16
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    Thanks all. The other engine mount was sitting at the same height as the new one so I figured it was okay and have done the trans mounts. Will look at the diff mounts. Seems the most likely culprit... Annoying that new mounts are NZ$209+ tax here so I'll have to order from the states and wait for shipping!

  17. #17
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    Sorry to hear of your trials. I too had a thump in the rear of my 93 850 automatic, and spent a lot of time and $$$$ chasing it. I replaced motor and transmission mounts, all the differential rubber bushings, including the nose strut. I also replaced the sub frame to body bushings, and the trailing arm bushings, adding CSI front bushings. I replaced the driveshaft, as the front u joint was notched, and the center bearing was dry, and the rear cv seemed loose. I even upgraded to CSI sway bars while I was at it, with new end links. Then while I was at it, I installed a new LSD differential with 4.10 M gears built by Jim Blanton of Performance Gearing, which I do like very much. Unfortunately after all this, I still had a thump, or clunk in the rear! So, as I was also having some Limp home, and Trans program failure problems I then dug into the DK's. The motor armatures and brushes were just a hunky mess! I took them all the way down to the gears, and this is where you must be very careful. The wiper arms are a press fit, and pull straight up and off, BUT if you don't reinstall them correctly, and if they are clocked differently between the two DKs you will have problems! Since I did mine, the thumping has largely gone away. Good luck to you.

  18. #18
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    I have a spare set of refurb'd DKs. Will swap them when I do the banjo bolts.

  19. #19
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    Swapped the DKs this evening for refurb'd ones and the 'thump' when throttling on and off is greatly reduced (throttle response is also better... Can't wait to drive it on a longer, faster journey!). Pleasantly surprised that the replacement DKs did not need syncing.
    Last edited by jeffbebe; 01-13-2015 at 04:41 AM.

  20. #20
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    Quote Originally Posted by jeffbebe View Post
    Swapped the DKs this evening for refurb'd ones and the 'thump' when throttling on and off is greatly reduced (throttle response is also better... Can't wait to drive it on a longer, faster journey!). Pleasantly surprised that the replacement DKs did not need syncing.

    Hi there, I was searching the E31 forums for problems on transmission clunk and came across this thread.

    I have the following issue:
    I just took the 850 for a run to determine where the clonking sound was coming from.

    1. Automatic gear in "D" position - traveling at 100km/h there is immediate clunking sound when you step on and off accelerator
    2. Automatic gear in "3" position - traveling at 100km/h there is no clunking sound when you step on and off accelerator

    Also, what is DK? so I may look into it this week.

    Appreciate your response

  21. #21
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    Quote Originally Posted by monza5995 View Post
    Hi there, I was searching the E31 forums for problems on transmission clunk and came across this thread.

    I have the following issue:
    I just took the 850 for a run to determine where the clonking sound was coming from.

    1. Automatic gear in "D" position - traveling at 100km/h there is immediate clunking sound when you step on and off accelerator
    2. Automatic gear in "3" position - traveling at 100km/h there is no clunking sound when you step on and off accelerator

    Also, what is DK? so I may look into it this week.

    Appreciate your response
    DK = Throttle body.
    The torque converter can also cause a clunk, as it releases or engages.

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