C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

91 automatic downshift clunk

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Old Feb 7, 2014 | 02:40 PM
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Default 91 automatic downshift clunk

anyone had this problem? when coming to a stop and transmission shifts into first gear I get a clunk somewhere in the drivetrain. transmission shifts fine and there are no other symptoms.
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Old Feb 7, 2014 | 04:07 PM
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Originally Posted by mmccarson
anyone had this problem? when coming to a stop and transmission shifts into first gear I get a clunk somewhere in the drivetrain. transmission shifts fine and there are no other symptoms.
my 91 has it "somewhat," I have to really listen to hear it, generally. I suspect it is worn half shaft or drive shaft U joints. looked at that, and didn't notice anything obvious. when the weather is 90 degrees, I may inspect it further.
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Old Feb 7, 2014 | 06:43 PM
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Default Clunk

Does it happen if you shift from neutral into 1st or reverse? If you accelerate and let off the gas pedal, does it happen? If it does, I'd look into u-joints and rear end first. Next I'd start looking into the various mounts and insure they're tight.
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Old Feb 7, 2014 | 07:29 PM
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downshift clunk - common issue with some 90 and early 91 automatics. there was a TSB issued sometime in 91 addressing the issue, and a dealer installed kit for the fix, but those days are long gone. anyway, here's a link to the TSB -

http://www.corvetteactioncenter.com/...k#.UvV5HGiYYiQ

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Old Feb 7, 2014 | 07:44 PM
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from the link that Joe C posted, if your auto was built after May 20, 91, it has the fix. there is a link to get the info on your vehicle number if you are interested.
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Old Feb 7, 2014 | 07:49 PM
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Yep...
I agree with Joe.
Internal. Its possible that a good performance tranny shop would have the springs and the know-how to get it straightened out.

To eliminate the u-joints, start up and shift between rev and any for gear. See if there is the same clunk/clang noise as the trans grabs the drive-line. If there IS, u-joints are in order. The more of a "clang" the more likely its time for a joint. Clunk is internal, clang is drive-line. Seriously..
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Old Feb 9, 2014 | 04:24 PM
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thanks to all for your input. I have a great shop that I use and I will pass the tech bulletin to them when they check it out.
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