Intermittent Knocking Noise - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-07-2009, 10:13 PM   #1
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Default Intermittent Knocking Noise

After the GM dealer stuck in a new tensioner pulley in my '93 SSE */C, I started getting kind of a hollow sounding knock at times when shifting into gear, accerlerating from a stop & when hitting bumps. The noise is coming from the back of the engine, underneath & to the mid right.

I took it back & they diagnosed it as a broken left front lower motor mount that was causing the RF motor mount to jump excessively. Replaced the broken mount & still had the knocking as before.

Took it back again, they checked for anything loose, & came up with with a bad RF endlink. I'd actually already had the LF endlink replaced with a K5255 (Moog) at Firestone after it had broke when banking on a right turn after the pulley work at the GM dealer, so I took it back to Firestone & had them replace the RF endlink with the same.

But I still have the knocking sound as before, except it now doesn't seem quite as loud & frequent - it'* mostly now when shifting into forward 1st thing in the morning & when hitting a series of bumps.

I'm sure it was something the GM guy did when he changed out the pulley. Afraid he somehow broke that mount & that damaged something else, &/or did something to the stabilizer bar. Is that possible for that job? Any ideas?

Last edited by boa12; 04-07-2009 at 10:16 PM.
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Old 04-07-2009, 10:20 PM   #2
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Does it sound like this?

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Old 04-07-2009, 10:29 PM   #3
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Quote:
Originally Posted by Danthurs View Post
Does it sound like this?


lol - looks like a good candidate. what is it? :crazysmile:
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Old 04-07-2009, 10:32 PM   #4
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If that is the sound it'* a bad coupler in the supercharger. Take the belt off and try this simple test.



If you feel play you will need a new coupler.
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Old 04-07-2009, 10:51 PM   #5
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Sorry Dan, was just trying not to go into too much unnecessary detail. I've had a lot more done by that dealer including putting on a new (rebuilt) charger. Of course they couldn't just change the coupler.

This all started with the rattle noise, which they 1st tried to correct by putting on new belts, & when they got the part in a new tensioner pulley. It was after the pulley install, that I got the knock noise.

The charger sounds fine now. The tensioner pulley moves some w/ the engine running, which I think is normal.

It'* hard for me to locate the knock from the driver'* seat. But it seems to come from the back of the engine, underneath & more to the right.
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Old 04-07-2009, 10:56 PM   #6
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Could be your water pump or power steering pump. Pull the belt and try turning them by hand.
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Old 04-07-2009, 11:06 PM   #7
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Could be your water pump or power steering pump. Pull the belt and try turning them by hand.
They replaced the water pump too in the 1st go 'round. I don't even know enough to take the belt off. This seems more like it'* from engine movement, since it happens when hitting bumps & putting in gear.
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Old 04-07-2009, 11:10 PM   #8
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Check all the pulleys. If you have a friend to help you. Have him put it in gear while you watch the engine. Watch for play and slop. Watch all the engine mounts.
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Old 04-07-2009, 11:31 PM   #9
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Quote:
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Check all the pulleys. If you have a friend to help you. Have him put it in gear while you watch the engine. Watch for play and slop. Watch all the engine mounts.
Will do, again. Had my girlfriend shift while I watched it & though the engine moved a bit didn't get the knock. Best thing would be to take it back to the dealer & do it in front of them. They always just do a half-assed diagnosis & throw parts at a problem.

Thanks, Dan!
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Old 04-08-2009, 02:12 AM   #10
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In the meantime, anybody have any ideas on how a mechanic breaks an engine mount & what else he might have screwed up by just changing a tensioner pulley? It took him like 3 hours to do it, & then he releases it with a broken mount. Not to mention the LF endlink broke off right after.
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