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Stumped, New Vibration! (yes, I know...)

 
Old 01-26-2019, 12:31 PM
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txcharvel
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Default Stumped, New Vibration! (yes, I know...)

I know there are tons of posts on this, but I'm really stumped.

A couple days ago, a new vibration started on my '86 NA. It sounds and feels like the exhaust is loose, but checked this morning all is tight as it should be. The vibration is always there but most pronounced around 2800RPM, subsides and comes back around 3100 RPM. The vibration is there when revving in neutral as well.

In the past year, I've done all belts (timing and balance shaft), motor and transaxle mounts, clutch, and exhaust hangers. The car literally drove and felt like a new 944 and this new vibration is driving me bonkers!

I've checked the starter and exhaust, I'm about to pull the covers off and check the belts. I know it could be any number of things, but wanted to get some ideas here. Thanks


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Old 02-05-2019, 11:14 PM
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944ATX
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I had a vibration that was internal to the original Cat and was eliminated when....I replaced the cat

the external exhaust fittings were all fine but the cat was so clogged that I think it was creating a harmonic vibration.

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Old 02-06-2019, 04:41 PM
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Thanks for your reply. My vibration is fixed and I never would have guessed the cause. Didn't get much interest here so never followed up. Thankful this was an easy fix, but it's also bizarre. The lower balance shaft was out of time by almost 90 degrees. I pulled the balance belt tensioner and it was very stiff. You could barely turn it, but it wouldn't spin. I put it back together with an old tensioner and the same belt, all is good. I'll order a new belt and new tensioner and change it out in a couple weeks. Still really bizarre. This tensioner was installed brand new in July 2018.
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Old 02-06-2019, 04:45 PM
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Default Pics of balance belt tensioner...

You can tell this tensioner is pretty much new. As I mentioned, installed in July 2018


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