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Knocking under load

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by mememe, Aug 10, 2011.

  1. mememe
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    mememe Member

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    [Aug 10, 2011]
    When I boot it in the lower gears I can hear a knocking sound from roughly under the handbrake area. It is not very loud (but definately noticeable) and knocks about 4-5 times in a second but only when accelerating. The acceleration feels smooth. A mechanic friend of mine has had it on the ramp but cannot find anything untoward.

    Any ideas please?
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  3. AU01 A4
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    AU01 A4 Member

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    [Aug 10, 2011]
    are all your tyre the same make, model and size? as it is were your central diff is, if your tyre are not with in 4ish mm it will play up.
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  4. snowball1969
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    snowball1969 Member

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    [Aug 10, 2011]
    is this a 4 wheel drive if so the prop shaft could be the culprit
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  5. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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  6. Az
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    Az Hard slammed!

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    [Aug 10, 2011]
    Going by his sig I'd say it's a 4 wheel drive ;)

    I agree with AU01 A4, the quattro system can be very sensitive to tyre tread depths or non matching profiles. As little as 3mm difference between tread on any tyre can upset the 4 wheel drive system and put strain on it. If for what ever reason you have different profiles between tyres this can also cause problems to the quattro system.

    As regards to the prop shaft as snowball mentioned, I'm not 100% familiar with the prop shaft on the audi's, but of they are anything like BMW's then they have a big rubber donut mount between the gearbox and the prop shaft itself which will be literally the location of the knocking that you describe, so if it's split or perished it can cause a lot of movement when accelerating hard, and on the BMW's they are have a metal shield just over the prop shaft and under the floor of the car, so with movement of the prop with a knackered donut mount that can knock against each other.
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  7. mememe
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    mememe Member

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    [Aug 11, 2011]
    Thanks guys so far. The tyres are all the same and about the same tread depth.

    Update: The noise is worse when pulling away fast around a T junction. When doing this it becomes apparent that the noise is from the footwell are drivers side. Sorry for miss directing you.
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  8. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Aug 11, 2011]
    Does it do it worse on left or right hand lock?
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  9. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Aug 11, 2011]
    what engine size have you got?
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  10. swarcup
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    swarcup Well-Known Member

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    [Aug 11, 2011]
    same here i also have this noise on take off, so far ive had 3 garages look to no avail and i have now started throwing parts at it which include all 4 arms, drop links and track rod ends both sides. Good luck
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  11. Turkster
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    Turkster Bro.Paul 2.5TDI Quattro Sport

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    [Aug 11, 2011]
    Engine mounts can cause this as the engine will lift and clunk back down under load and the mount are in the same area as the rest of the links that you are changing.
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  12. abyrne153
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    abyrne153 Member

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    [Aug 11, 2011]
    I had a similar problem on my Quattro. Believe it or not it was a small stone lodged in the rubber gearbox mounting. I only got this hard knocking under acceleration and it took me a while to find the culprit. The mounting is cup shaped so stones and debris can get stuck there especially as the fibreglass cover on mine was broken and had been removed. Get the car on a lift and check the mounting carefully.
    #11
  13. mememe
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    mememe Member

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    [Aug 11, 2011]
    Hey I remember seeing a stone lodged somewhere in the gearbox/surround. I'll check up on it and let you know how I get on. Thanks
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  14. mememe
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    mememe Member

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    [Aug 11, 2011]
    Thanks for this. I have had some other issues today which I will make a new thread for and post a link. But basically, the car went into limp mode today and several fault codes were recorded. One of which was 17996 - 'Engine mount solenoid valves, open cct'

    This went away when reset. Limp mode then went away for about 5 mins then came back. I stopped, restarted the car ok, and it never came back. The only other thing of note was, it was absolutely bucketing down when I initially got the problem, then it dried out very quickly.

    Does any of this make you think more......or less that it could be the mounts?

    Thanks
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  15. mememe
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    mememe Member

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    [Aug 11, 2011]
    Worse on right lock
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  16. mememe
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    mememe Member

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    [Aug 11, 2011]

    1.9 TDI SE Quattro Avant 02
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  17. mememe
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    mememe Member

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    [Aug 11, 2011]
    Link to new thread
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  18. mememe
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    mememe Member

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    [Sep 12, 2011]
    OK I have it. It was an engine mount that was not secured correctly See here.

    Thanks to all for your help.
    #17

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