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3/29/14 3:35pm - Original Message: 'thump'
swany 80vette
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Vette(s):
1980 c3

Joined: 3/24/2014
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took my car out for a drive today, finally a nice day. anyway noticed just a little bit of a bump, bump, bump. Not very loud at al. Only seems to do it when you let off the gas. Like when there is no torque at all on the drive train. A knuckle or some type of bushing or something ? Not bad yet but I suspect it will get worse. Any ideas ?
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3/29/14 5:20pm - Reply: 'Re: thump'
johnu
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Scottsdale, AZ - USA

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1981 Corvette Two-Tone Claret color, 4 spd, C7 Vert

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U-joint?
I had one snap off a strap and was held on by the other side that made some noise.
 
 


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3/30/14 11:00am - Reply: 'Re: thump'
jdgrant Gold Member
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HOT SPRINGS NATIONAL PARK, AR - USA

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1978 (25th Annv. Edition)Red, Black interior, 4-Speed Transmission, L-82, Power & Air, Very Rare Option Package(Only 145 Red 1978s with a 4 speed trans) & Very Original Car, with original Window Sticker, Bill of Sale and all documentaion.

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U joint would be my guess too. What is there, about 6 possible culprits? But, would likely say the drive shaft is the first place to look.

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3/30/14 11:16am - Reply: 'Re: thump'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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First thing I would check would be the front differential "snubber" mount. If it is worn, or lose, it could cause the diff to flop on decelleration like that. Could also be the front trailing arm bushings, hub bearings, u-joints, etc., but I would check the diff bushing first, and go from there. Thumbs Up

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3/30/14 11:34am - Reply: 'Re: thump'
swany 80vette
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That was my guess too. Will have to get her on the hoist and check it out. Thanks for your opinion
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3/30/14 3:03pm - Reply: 'Re: thump'
dads2vette Lifetime Member
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Ash Fork, AZ - USA

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This reminded me of a story.  Years ago a friend of my dads was driving his mg when he noticed a thumping and a strong burning rubber smell.  It took him a few weeks to take it into a shop because his knowledge of cars included the wisdom that cars will fix themselves eventually.  Turns out he ran over a skunk and it was hitting part of the rotating assembly of the drive train when decelerating.

Steve, you're sure you didn't hit a skunk?Wink


|UPDATED|3/30/2014 1:03:14 PM (AZT)|/UPDATED|


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3/30/14 6:24pm - Reply: 'Re: thump'
swany 80vette
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Ha ha no skunk
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3/31/14 12:25pm - Reply: 'Re: thump'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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Otay....no skunk, but....perhaps something else?



LOL  LOL  LOL

Reminds me...long time ago, Mama ran over a huge plastic bag in her Burick, but she dint realize that she had. A day or so later, she told me it was vibrating really bad. I crawled under it and saw this huge plastic mess wrapped around the driveshaft, and on the diff. It had already ruined the u-joint in the rear, and the pinion seal was just pouring gear lube.  From that day on, she ALWAYS looks behind the car after she runs over a bag....even a candy wrapper! LOL

|UPDATED|3/31/2014 10:25:46 AM (AZT)|/UPDATED|


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Joel Adams
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5/6/14 8:42pm - Reply: 'Re: thump'
swany 80vette
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1980 c3

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The snubber looks a little old but didn't look that bad. I just tried feeling slop in the u joints, driveshaft and axles. Is there a better way to check the u joints on the axles and drive shaft ? Greased them all while I was under there , boy that one at the back of the drive shaft is fun to get at.
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5/7/14 11:37am - Reply: 'Re: thump'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
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swany 80vette said: The snubber looks a little old but didn't look that bad.

Did you look at the upper bushing, or just the lower?(#5753K in this diagram) A noise on deceleration would be the upper bushing. It's kinda tough to check either of them without actually removing them. You might be able to pry the snout up/down with a large screwdriver/prybar to get a better idea of the condition.



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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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