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Thread: Front eng thunk when going over small bumps

  1. #1
    Join Date
    Feb 2005
    Posts
    14

    Default Front eng thunk when going over small bumps

    I did a search and couldn't find an exact match to my problem. I have a 95 525i with 69K miles. When going over small bumps in the road, like the curb in front of my driveway, it sounds like a solid thunk. Here is what I know.

    I installed new Bilstein touring shocks all around.
    Factory springs are installed (all suspension is factory).
    I have crawled under the car and looked for loose fittings.
    I have double checked all the bolts/nuts that I had off for the shocks.
    I have tighted the strut housing nut (holds strut in housing).
    Top nut on shock is tight.
    Both wheels do it the same.
    Car drives straight down the road (recent alignment).
    Rear upper shock mounts were replaced with shocks.
    Pushing on the front fendors the car responds as it should, smooth and responsive.
    New Toyo Proxy TPT tires.

    Almost seems like something isn't right with the front to back motion of the front suspension (which should be almost zero movement). The up and down is smooth.

    One question: Besides getting a shimmy at 50mph (which I haven't noticed), what is the symptom of bushings wearing out?

    I would like to hear your best guess on what my problem is. Thanks

  2. #2
    Join Date
    Jan 2004
    Location
    Boston, Ma
    Posts
    441

    Default

    Sway bar links are your best bet. Does it happen going into turns sometimes too? If it is then that is probably your problem, get under the car and check the boots and give them a good shake. Its a cheap part if thats the problem, like $20 a pair.

  3. #3
    Join Date
    Feb 2005
    Posts
    14

    Default Sway bars seeeeem okay

    The sway bars seem okay. When I jerk on them they don't seem to move much, if at all. I like the idea of them being cheap, maybe I will try them. thx


    Quote Originally Posted by bjl4776
    Sway bar links are your best bet. Does it happen going into turns sometimes too? If it is then that is probably your problem, get under the car and check the boots and give them a good shake. Its a cheap part if thats the problem, like $20 a pair.

  4. #4
    Join Date
    Oct 2004
    Posts
    3,395

    Default

    Two thoughts:

    1) If one of the fasteners for a sway bar link is even remotely loose, it will cause the bump-thunk problem. Before I installed my Sachs kit, I slightly loosened my pass side sway link at the bar, promptly forgot to tighten it back up, then spent a few days riding around CONVINCED that one of my (new) u/l control arm bushings were gone. When I pulled the wheel off again to do the sachs install, I realized that the nut wasn't completely tight and felt like an idiot. I suppose the sway bar bushings could be shot, but you'd have some weird handling and other noises (stop/go) going on, I think.

    Edit: sway bar ball joints could also be bad (any cracked rubber boots?). I can't wiggle mine when the car's off the ground. They've got to be quite rigid as that part of the suspension functions as the solidifying link between the two sides on the bottom end.


    2) The steering box mounting bolts (to the subframe) can loosen up over time and cause a clunk in low speed turns (check bmwe34.net)

    best, whit
    Last edited by Kalevera; 04-05-2005 at 10:37 PM.

  5. #5
    Join Date
    Feb 2004
    Location
    Bellingham
    Posts
    380

    Default

    Sway bar links will be under heavy stress unless both sides of the front suspension are at equal positions relative to eachother. If you jack one side of the car up, the links will appear stiff as hell.

    Given how the problem is described, there's not much it CAN be aside from the endlinks. It's remotely possible that a strut collar nut (which holds the strut insert in place) has become loose; but this is a bit more of a longshot than the endlinks.

    As has been said, the bolts on the endlinks must be tight. For whatever (dumb) reason the shaft on the endlink ball joints doesn't match the bore of the holes on the swaybar. This little bit of play is more than enough to make noises.

  6. #6
    Join Date
    May 2004
    Location
    Sydney, Australia
    Posts
    2,699

    Default

    yep, check the swaybar links, Your getting excellent advice from intelligent gentlemen.

  7. #7
    Join Date
    Feb 2005
    Posts
    14

    Default I'll try the links first.

    After work I will crawl back under the front end with 15mm wrenches in hand and check the swaybar links. I might go ahead and get a new set coming. Give me some time and I will send out an update. thanks for everyone's advice. Paul

    Quote Originally Posted by BigKriss
    yep, check the swaybar links, Your getting excellent advice from intelligent gentlemen.

  8. #8
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,749

    Default Paul

    to check them correctly get the front on ramps, go under each swaybar end by the link and push straight up and down. It will be obvious if something is loose or worn.

    as for the rest of the steering if you get shimmy is is not nesessarily from old bushings but can be caused by any play in the tie rod ends, drag link or idler arm bushing. This is a lot harder to check for as I had to get mine on a hoist and it was a 2 person job to locate any play. Sure enough I have a loose tie rod end and play at the pitman arm.

    Good luck
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  9. #9
    Join Date
    Feb 2005
    Posts
    14

    Default Front suspension feels tight

    I jerked on the sway bar links the best I could while lying next to the car. I know this isn't as good as being underneath with the car up on ramps, but they sure felt solid..... Tomorrow I will have more time and will put the car on ramps. Either way, I ordered sway bar links from BMA, great price, slow delivery estimation (next week).

    I want to make clear that it doesn't feel like something is really out of wack, just on larger that normal bumps (pot holes and curb like heights) is when I feel the harder than expected noise/jolt. I might have mislead a few with my first description.

    thanks again, Paul


    Quote Originally Posted by pshirley
    I did a search and couldn't find an exact match to my problem. I have a 95 525i with 69K miles. When going over small bumps in the road, like the curb in front of my driveway, it sounds like a solid thunk. Here is what I know.

    I installed new Bilstein touring shocks all around.
    Factory springs are installed (all suspension is factory).
    I have crawled under the car and looked for loose fittings.
    I have double checked all the bolts/nuts that I had off for the shocks.
    I have tighted the strut housing nut (holds strut in housing).
    Top nut on shock is tight.
    Both wheels do it the same.
    Car drives straight down the road (recent alignment).
    Rear upper shock mounts were replaced with shocks.
    Pushing on the front fendors the car responds as it should, smooth and responsive.
    New Toyo Proxy TPT tires.

    Almost seems like something isn't right with the front to back motion of the front suspension (which should be almost zero movement). The up and down is smooth.

    One question: Besides getting a shimmy at 50mph (which I haven't noticed), what is the symptom of bushings wearing out?

    I would like to hear your best guess on what my problem is. Thanks

  10. #10
    Join Date
    Nov 2004
    Posts
    445

    Default

    It is *most likely* the 22mm nut that secures the strut to the mount is NOT tight. It looks tight when the car is set flat without ramps or jacks. But if you use a big wrench to turn it, the whole middle rod will turn. How to hold it ?.

    Special monkey wrench below to hold it when you get a few turns in the 22mm nut. When new springs/struts were installed, this is usually the case. This nut need to mildly compress the springs a little during rest. If not, the rebounded spring will raise the front a little. The car, when loaded has about 3 to 6 mm play due to that "raised" REBOUND , so clunk. Then it stays there cos the car is loaded and that play is going. When you park and get off, it rebound and raises again!. This repeats and gets annoying.

    Another possiblily is the steering link below the driver side, its about 2 mm lose (needs 2 or 3 turns more), this causes a minor clunk on bumps.

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