Heavy vibration under hard braking

Discussion in 'E46 M3 (2001-2006)' started by Jimbo25, Apr 17, 2019.

  1. 17 Apr 2019 at 12:37 PM #1
    Jimbo25

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    Afternoon chaps and chappesses,

    Got an interesting issue with my E46, when braking hard the thing shakes like a shitting dog, to be polite. It's interesting (I think at least) because the usual culprits, such as worn rear wishbone bushes, wheel bearings, hub cleanliness and imo brake discs are all A-OK - in fact mostly brand new. I've got Powerflex rear wishbone bushes (6k miles max) relatively fresh wheel bearings and therefore hubs ~20k max I'd say and a D2 6 pot brake kit with Bluestuff NDX pads - I don't think these have warped in any way / disc are clean.

    Also got all new track rod ends and steering ball joints last year (6k miles) - Top mounts OK and new B12 shocks / Eibach springs all round.

    My suspicion, despite it having just received a clean MOT ticket, is that the ball joints on the wishbones have got some wear in them, that only present itself under braking. I wonder this, as I did have the same vibrations, albeit lesser, on my old OEM braking system. Either that or the Redstuff pads but I can't quite believe that the pads could be the issue with 2 different pad shapes, material and disk size/thickness.

    Welcome any thoughts on my diagnosis, sadly it's a pretty expensive change to try without knowing 100%
     
  2. 17 Apr 2019 at 12:49 PM #2
    Iatm

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    If its shaking that bad under braking ONLY then its more likely to be the discs even though you think they are ok or a sticky caliper. go out for a 20 min drive, do some braking including hard braking and get back and get a feel for a heat off each disc, you will quickly see which one is sticking, the heat will be significantly more.
     
  3. 17 Apr 2019 at 1:05 PM #3
    Jimbo25

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    Sorry should have said, been round them all, and they're all of a similar temp. I know the fronts are renowned for sticking but don't think it'd be an issue with relatively new 6 pots.

    Should also say I get no vibration at any speed to suggest a tyre or wheel balance issue, only ever braking.
     
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  4. 17 Apr 2019 at 1:22 PM #4
    Loony

    Loony On the path

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    lower arm ball joint since you have said all the others are solid!

    I would have said Warped discs or Rear Lollly Pop Bushes are fooked, but you said they are all fine!
     
  5. 17 Apr 2019 at 1:32 PM #5
    GolfDuck

    GolfDuck Staff Member Moderator

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    Is the shaking coming through the steering, the brake pedal or the whole car?
    Is there any steering wheel movement at all under light braking?
    Is there any steering wheel movement whilst driving slowly without braking?
    Also have a bounce on the front end. Even new shocks can have weak or failing dampers.
     
  6. 17 Apr 2019 at 1:37 PM #6
    Jimbo25

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    Cheers GolfDuck
     
  7. 17 Apr 2019 at 1:45 PM #7
    GolfDuck

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    Suspension does seem more likely. As above, the bottom arm ball joints could be suspect perhaps.
    The slight oscillation whilst braking lightly might make me lean more towards discs or sticking caliper piston or master cylinder, possibly.
    In my experience when the steering wheel tugs slightly one way then the other whilst driving slowly and not braking it has tended to be a sticking caliper piston (or one time a master cylinder that wasn't fully releasing) though as you say you would expect one wheel or more to be much hotter than others. Unless they're all hotter than they should be for the braking you've done :)
     
  8. 17 Apr 2019 at 1:56 PM #8
    GolfDuck

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    Also worth a check is the inner bush on that same bottom suspension arm. With the engine heat they take they can deteriorate.
     
  9. 17 Apr 2019 at 4:22 PM #9
    leipziger

    leipziger A mere Chipper

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    Got the same exakt same problem, my disc are fine (measured with a gauge) but if the disc get warm, they wrap a bit and cure very heavy vibrations under hard breaking. I think this happens when you had a hard brake and stayed on the brake. (Pre owner was a d**b)

    Will upgrade my brakes soon with new CSL Discs, because it’s not driveable this way

    BR,
    Julian
     
  10. 17 Apr 2019 at 4:57 PM #10
    paul46

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    First thing I would look at is the powerflex. They are utter crap and the heat on the manifold side destroys that Bush.
     
  11. 17 Apr 2019 at 5:36 PM #11
    Jimbo25

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    I will of course check them Paul - I'd heard this but asked at Geoff Steel (as they recommended them) and they said they never had any issues. I did used to get it on the old (assume stock) rear bushes, but then they were shagged as it came up on the MOT, hence the change.

    I've ordered a new Jack, as yet I haven't actually had it up and checked anything, just going off how old components are.

    Just out of interest, Racetracker.de suggests your car when I search for TF pics of mine, I wondered why 20 pages of pictures came up when I've only done 3 trips lol
     
  12. 17 Apr 2019 at 5:39 PM #12
    Jimbo25

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    It's a good point, I'd read about harder pads leaving deposits on the discs when used lightly i.e. around town and that a decent warm up and few hard stops cleared them up, but I can confirm after the ring they definitely got hot enough and if anything got worse! I'm open to the disc or pad issue, just find it bizarre if the issue traveled from the OEM discs and calipers onto the new brakes with new wheel hubs on.
     
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  13. 17 Apr 2019 at 6:00 PM #13
    monkeyboy

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    I had this on my discs a few months back were fine one minute then all of a sudden awful vibration under braking done a few runs with hard braking to clear them and they were fine again and ever had it since worth a shot before you start shelling out for anything
     
  14. 17 Apr 2019 at 6:56 PM #14
    Jimbo25

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    I did two laps of the ring on Sunday, I think that should have sorted it (for a long time I was hoping the same and they’d clear up but to no avail)
     
  15. 17 Apr 2019 at 7:54 PM #15
    monkeyboy

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    That’s a pain mate, have you figured out what’s causing it yet? Must be discs surely ?
     
  16. 17 Apr 2019 at 8:22 PM #16
    Jimbo25

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    Sorry didn't type that too well - I was hoping the laps would sort it, but the issue is still there - I'm leaning towards suspension I think (forgive the pun)
     
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