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Knocking Sound from Tranny Area 200

posted by  MrNabisco on  Sun Apr 16 10:36 CST 2017
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last visit: Wed Oct 22 12:36 CST 2014
[RELATED]

Hi Folks,

My brick has started making a new noise.

At low speeds I can hear a slight rhythmic knocking sound coming up from below the center console, in the area of the rear of the transmission. At faster speeds engine and road noise blocks it out. I've coasted the car with the motor off and can hear the sound changing with the speed of the car, so I'm guessing it is tranny/driveshaft related. I'll take a look under the car to see what I can see.

So what could be the possible sources of the sound?

Tranny? It is an M47 5-speed with 208kmiles, filled with Volvo fluid. It has been working fine. No whines or hard shifts.

Drive shaft? I just had a new driveshaft carrier bearing/rubber bushing installed. Did not do the guibo or front u-bolt as they looked OK.

Could the sound be guibo related?

The sound is not the same as when I had a bad rear shaft u-bolt. That was a stronger thumping. This sound is a lighter taping, but there and consistent with shaft rotation.

???

Any suggestions greatly appreciated.

Bert







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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    I found the knocking source... Loose O2 sensor wire hitting the quibo.

    Just couldn't see it happening until I got under at the right angle. Was spooked it could have been the quibo, since I chose not to swap it. :/ And I'm always listening for sounds from the M47.

    Thanks again to all who responded.

    Bert



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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    Thanks for the responses.

    I'll get under the car and get some hands on to the bearing and quibo to get a feel and look for something loose.

    Just to ask, would this slight knocking sound be any kind of a tell that the M47 is starting to fail?

    Bert



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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]


    Guibo may look okay but subtle cracks between the bolts can be hard to see. Also check that the bolts look properly aligned in relation to each other. Guibo might crack and warp a little before totally coming apart...

    Long shot - Bad tranny mount causing a knocking sound?



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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    Bert,

    Have you tried raising the rear of the car, starting the engine and then putting it in gear, jumping out and watching the driveshaft turn?

    I saw a video on this very thing and it was amazing to watch things move around. In the video it showed the center carrier rubber housing moving all over the place thus the problem.

    Was the center carrier rubber housing oriented correctly front to rear as it does matter.

    Let us know what you find out.

    Matt


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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Matt,
      Interesting suggestion. The car is in a gravel parking lot, so setting up a safe lift to watch the drive train would be problematic. I'm trying to think of a way to do that and turn the drive train without actually running the motor. ???

      I'm pretty confidant the carrier bearing and rubber housing were installed correctly. I've driven about 4-500 miles since it was installed and the noise only became noticeable recently.

      Looked under the car and the quibo looks intact. Nothing hanging on the driveshaft to make a noise.

      I may need a brick guru to have a listen. This noise I can't pin down.

      Bert



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Since the Center Support Bearing was just done 500 miles ago I would look closely at the Mounting bolts to the bottom of car. If the hardware came out rusty and crappy, they may have been reinstalled cross-threaded and after 500 miles came loose. I'm guessing/hoping the installer put the two driveshafts together properly and you are not feeling misaligned shafts.
        Check the hardware at the front Rubber (Guibo)and rear 'U' joint.

        --
        '75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        3/4" Plywood. Jack Stands
        you don't have to risk anything other than a mirror to see what's up



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