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Knocking sound back - sounds like subframe

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    Knocking sound back - sounds like subframe

    Hey guys,

    I'm a little troubled. I've noticed in the last little bit I'm getting a knocking sounds, apparently from the right rear, like I did before I did the subframe bushings.

    When I first did them about a month ago, that knocking sound had gone away.

    The only thing I can think of that I may have done wrong was the tightening of the 22mm nut for the subframe. I couldn't find a torque spec in Bentley, and I didn't notice the one at the bottom of the RTSAuto article on the bushings - 70 ft lbs. In the article he says: "Subframe to body (Big bolts) – 94.9nm (70ft lb) <<< I found this torque to be fairly low, most of the community agrees to tighten the shit out of the nut with a normal size breaker bar (like you would a lug nut)".

    Soooo, I talked to my buddy who was helping me. He does machine assembly, and he said according to torque specs, a nut that size could be torqued as high as 170 ft. lbs. I tightened it as far as I could manage with my big 250 ft lb capable Husky torque wrench, but didn't make it that far. I'm guessing I'm somewhere between 100-150 ft. lbs. I haven't had a chance to check it.

    I've taken a look at the bushings while I had the car on ramps, and things looked ok from that vantage. I haven't had a chance to suspend the car, leaving the subframe in air yet.

    I'm a bit miffed that the knocking sound is back and I'll be really annoyed if something went wrong with the bushings. I know we didn't damage them during the install into the frame - we'd used a mallet, soapy water, and had cleaned the subframe holes well with a wire brush, and they fit in beautifully with a few rubber mallet whacks.

    Any suggestions here?
    Estoguy
    1986 BMW 325, Alpenweiss ~ "Elsa"

    Need a photographer, come visit my site: http://estoguy.wix.com/unique-perspectives

    #2
    Could it be rear shock mount clunking sounds? That's usually what I read about when I hear about rear "knock" or "clunk" kinds of problems.

    Otherwise I don't really have any insight. :(

    Som

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      #3
      If the bolt is tight, it's obviously not moving around. What is tightening it farther going to accomplish?

      What Som said, you probably just need some upper shock mounts.

      Comment


        #4
        Things that could clunk in the rear:
        Upper shock mounts
        Lower shock bushing/bolt
        Loose caliper bolt
        Bad trailing arm bushings
        Loose differential nuts
        Cracked subframe at differential mounts
        Cracked unibody where subframe attaches.


        A helpful trick to finding suspension clunks is to lift the car in the air, and using a reasonably large hammer, strike the bottom of the tire upwards (to stimulate a jounce), and listen/look for the source of the noise.

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          #5
          How about the diff bushing? Or what about the drive shaft center bearing?

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            #6
            I tightened my delrin bushings to around 125 ft lb, no issues going on 3 months now. My exhaust hitting the under body sounded just like shot subframe bushings. Drove me mad until I poked around.


            RIP 02/25/15
            http://www.r3vlimited.com/board/show...16#post4356816

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