Engine mount diagnosis please (video)

Discussion in 'Engine' started by Troon, Mar 31, 2014.

  1. Troon

    Troon Hardcore MB Enthusiast

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    In my continuing vibration hunt, the finger of suspicion is now pointing at my engine mounts. I've taken a quick video of start-up, followed by applying a tiny amount of throttle in Drive and Reverse with the brakes on, then shut-down.

    I'd appreciate any input on this. The movement doesn't seem that extreme to me, but that doesn't exonerate them from causing/transmitting the vibration. The engine seems noisier inside the car than when I bought it, but no clunks or bangs (yet).

    https://vimeo.com/90518753

    Thanks in advance.
     
  2. Sp!ke

    Sp!ke Administrator Staff Member

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    By applying throttle in gear with the brakes on, the engine will move considerably - a better test would have been to just rev it a bit while in neutral.

    What makes you think that your engine mounts need replacing? Are you experiencing vibration or noises or something?
     
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  3. OP
    OP
    Troon

    Troon Hardcore MB Enthusiast

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    Summary of the problem, which feels somewhere between wind buffeting with a single window open and wheel balance.

    Characteristics:
    • Intermittent: sometimes barely there, sometimes feels like something’s very wrong.
    • Noticeable on smooth roads at 20–30mph, more so at 45–50mph.
    • Can get disturbing at autoroute speeds (85–90mph indicated), annoying when inContinent.
    • Noticed from purchase at 72k miles, now seems worse at 130k miles.
    • Felt through seat and floor at higher speeds, nothing through steering wheel.
    • Not affected by throttle position, gear selection: continues when rolling in neutral.
    • Idles smoothly in neutral or drive. Very slight occasional shake in D with HVAC off.
    Has continued through:
    • Alignment (76k)
    • New lower ball joints at front (76k)
    • New front lower control arms (n/s 76k; o/s 91k)
    • Two complete tyre changes with rim & balance checks each time
    • New disks and pads all round (128k except front discs: DIY, 75k)
    • New transmission mount (128k)
    • Two ATF changes (74k & 130k)
    • Swapping front & rear wheels
    My suspicions:
    • Propshaft: centre bearing; or shaft out-of-balance?
    • Suspension bush given up, allowing resonance?
    • Shocks shot? Suspension doesn’t seem bouncy, though.
    • Dodgy wheel (despite prior checks)?
    • Engine mounts…injectors… (despite no relation to engine speed/power)?
     
  4. grumpyoldgit

    grumpyoldgit Hardcore MB Enthusiast

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    That doesn't look excessive to me, but as Sp!ke says, rev it in neutral. Have you inspected the engine mounts to see if they have collapsed?

    Sorry I haven't seen any previous posts you may have made on this problem so forgive me if you've eliminated all/any of the following.

    Is the vibration evident with the car stationary? Possible gearbox mounting or exhaust possibly touching against other components.

    Is the vibration evident only whilst the car is moving? Possible prop shaft bearing/s and or mountings, or wheel bearing failing.

    Oops! You posted the above while I was typing my suggestions. :doh:
    I think I would be checking the prop shaft, both the hardy-spicer uj's and the centre mount. If there is a clean ring around any of the uj's, where the clip hold them in, it's a sign that the cup holding the needle bearings is slowly spinning and the bearing is shot.
     
    Last edited: Mar 31, 2014
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  5. kth286

    kth286 Hardcore MB Enthusiast

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    It could be geometry/alignment needs to be done.

    What is wear across all tyres like - even or uneven (each tyre).

    It maybe tyre wear seems even, but car could still be driving along road in a 'crab' like fashion ie. where the centre line of front wheels are not directly in line with the centre line of rear wheels.

    Setting up the car alignment means the rear of car is set up first, with rear wheels square to chassis centre line; then front wheels should be set from the mid point of rear wheels to mid point of front wheels.

    Draw the concept on a piece of paper to get the idea.

    I would be taking it to a recommended expert in car geometry - WIM comes to mind.
     
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  6. OP
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    Troon

    Troon Hardcore MB Enthusiast

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    It's had an alignment at 76k. It drives and handles very well, and I get 25-30k+ out of a set of tyres with completely even wear.

    I'll try to get under and take a look at the propshaft bearing and UJ; but Mercland have recently had a look and not found anything. They suspect tyres but I can't see that given its persistence through two sets.
     
  7. Sp!ke

    Sp!ke Administrator Staff Member

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    Also check the mounts to see if there is any signs they have been leaking as well.

    If it were my car I would probably change all the mounts as a matter of course. They aren't too expensive or difficult to change and after 130k miles you'll probably feel an improvement even if they haven't failed completely yet.

    When I changed them on my W124 it was like driving a different car.
     
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  8. grober

    grober MB Club Veteran

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    Propshaft centre bearing /mount would be my guess. :dk: Might be worth getting the propshaft assembly dynamically balanced at a propshaft specialist rebuilder?
     
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  9. OP
    OP
    Troon

    Troon Hardcore MB Enthusiast

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    I can only see one mount clearly without disassembly: no obvious faults, but I wonder if they're a bit tired. I changed the trans mount a few weeks ago, and the old one didn't look or feel any different to the new. This may have made the vibration very slightly worse, as if better support at the back of the engine is worsening the wobble elsewhere... :dk:

    That sounds tricky and expensive, particularly if it's not the cause. Any way to check the centre bearing mount statically? How much should it move about?

    I'd really like to pin this down without just throwing money around, but it's the sort of problem that needs constant exposure to recognize: not something I can immediately point out to a technician.
     
  10. grober

    grober MB Club Veteran

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    Usually the centre bearing is mounted in a rubber mount in a metal saddle bolted to the floor. Eventually this degrades allowing the bearing to move about a bit. Depending on the car it can be difficult to see as its often obscured by exhaust heat shielding. Rough test is simply to get a firm hold of the propshaft and give it a wiggle up and down---any excessive movement would be a sign the mount has seen better days- should move slightly as its supposed to dampen out vibration from the body. How relevant a low amplitude test like this would related to the high speed vibration of a prop shaft driving along the road I wouldn't know but I expect Mercland checked this. I have no idea how much it costs to balance a prop shaft nowadays but it might not be too expensive once its off the car.
     
    Last edited: Mar 31, 2014
  11. Kay-W212

    Kay-W212 New Member

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    Hi Troon,

    Have you sorted the problem.

    I have the same problem. My E220 W211 will shake side-to-side very lightly when stand still. I suspect the Engine Mountings to be the cause. I am getting these replaced in a couple of weeks and I am thinking to replace the transmission mounts at the same time.

    Please share your findings.
     
  12. OP
    OP
    Troon

    Troon Hardcore MB Enthusiast

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    Mine is sorted. Turned out to be either ball joints, tyres or wheel balance.
     

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