Odd thunking at low speeds, clutch engage/disengage

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  • ethirdy
    E30 Addict
    • Nov 2007
    • 406

    #1

    Odd thunking at low speeds, clutch engage/disengage

    Just recently I installed a new-to-me rear diff (3.73 LSD) and full exhaust, and I've got a low speed clunking when getting on and off the accelerator, and when putting the clutch pedal in and out. If I pump the clutch in and out it's almost constant and feels like it's in the middle to rear of the car.

    Background - car has new poly subframe bushings, poly TA bushings, new trans mounts, poly motor mounts, fresh Redline in the diff, new CSB, new guibo, new brake calipers and pads, new rotors, all new e-brake hardware.

    At first, I thought it was the CAB's - they're getting replaced along with CA's and sway bar end links, inner and outer tie rods, but this sound is more from the rear, and more pronounced with the clutch engaging/disengaging. Slower speeds only it seems - at higher speeds either I can't notice it or it's not happening.

    Possible issues - the halfshafts are leaking at the seals, on the ends that bolt to the diff, not the boots themselves. Not sure how to replace those, though I haven't really looked into it much, so it might be easy.

    Diff mount looked just fine, but it might be causing the clunking - not sure how I'd diag that.

    I'm fairly certain I did not thread the center locking collar from the front to rear driveshaft sections together - though I can't imagine that would cause the sound I'm getting.

    Exhaust seems secure, and I used all factory stuff, and even shaking the heck out of it (car stopped, foot on tailpipes) it doesn't hit, so for now I'm ruling that out.

    Ideas? Wed I'm going to drop the heat shield and inspect the csb - maybe I trashed it already, though the driveshaft u-joints were smooth as silk.
    Originally posted by alpinaclone
    Since the real economy is in the shitter, I say we start our own.

    This is how it works; you buy my junk, then I will buy more junk and so on so forth etc. etc. Think of the future of your children and buy my stuff.
  • LEANE30
    E30 Modder
    • Apr 2006
    • 838

    #2
    is it more of a "crack" or a thunk? ...poly rear subframe bushings were changed you said, if there is slack and the bolts through the frame & triangulating plates installed incorrectly it could have more of a cracking sound. ...other than that, if the rear dif mount is solid and the diff to the subframe is good and tight, pretty much the CSB is where i'd look. the guibo is good and the csb or REALLY BAD play in the diff, then i'm stumped
    ...what hasn’t been done to an m20 yet?

    m20 Oil Stencil

    Comment

    • ethirdy
      E30 Addict
      • Nov 2007
      • 406

      #3
      Originally posted by LEANE30
      is it more of a "crack" or a thunk? ...poly rear subframe bushings were changed you said, if there is slack and the bolts through the frame & triangulating plates installed incorrectly it could have more of a cracking sound. ...other than that, if the rear dif mount is solid and the diff to the subframe is good and tight, pretty much the CSB is where i'd look. the guibo is good and the csb or REALLY BAD play in the diff, then i'm stumped
      Plates and subframe mounts are perfect and torqued - those are off the list. Definitely a thunking - I'm leaning towards the diff mount or the CSB.
      Originally posted by alpinaclone
      Since the real economy is in the shitter, I say we start our own.

      This is how it works; you buy my junk, then I will buy more junk and so on so forth etc. etc. Think of the future of your children and buy my stuff.

      Comment

      • lennon
        E30 Fanatic
        • Jun 2008
        • 1416

        #4
        any luck? im kinda having similar issues...

        just changed the diff, somethings clunking and i cant figure out what

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