Clunk
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Joined: Dec 2020
Posts: 70
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From: Babson Park Florida
Clunk
Good morning,
I have the pleasure of owning a 1971 C3 in great condition that I use as my main stress release. My C3 is a convertible, has the stock 350 CI engine and 4-speed manual transmission.
I've started hearing a "clunk" noise when disengaging the clutch. If I keep the RPM's up, I don't get the "clunk" noise. I haven't crawled under the car yet to check things out and am looking for impute as to what I might look for.
Does this sound like a transmission, drivetrain or operator error issue to you?
Alan
I have the pleasure of owning a 1971 C3 in great condition that I use as my main stress release. My C3 is a convertible, has the stock 350 CI engine and 4-speed manual transmission.
I've started hearing a "clunk" noise when disengaging the clutch. If I keep the RPM's up, I don't get the "clunk" noise. I haven't crawled under the car yet to check things out and am looking for impute as to what I might look for.
Does this sound like a transmission, drivetrain or operator error issue to you?
Alan
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
Lets just assume your "71 has the original U-Joints installed for the last 51 yrs.
Lets also assume that in those 51 yrs, somebody drove it pretty hard off & on.
Keep in mind you have six U-Joints. Who knows how many times they were greased? With the car elevated, you need to check all three shafts for slop. Should not be any or very little movement in each shaft.
I highly recommend Solid Spicer's for replacement. Much-much stronger than stock and never need greasing.
Lets also assume that in those 51 yrs, somebody drove it pretty hard off & on.
Keep in mind you have six U-Joints. Who knows how many times they were greased? With the car elevated, you need to check all three shafts for slop. Should not be any or very little movement in each shaft.
I highly recommend Solid Spicer's for replacement. Much-much stronger than stock and never need greasing.
Race Director
Joined: May 2006
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You make no mention of whether the clunk is front or back of car. In addition to the previously mentioned u-joints, check motor mounts, transmission mount, and front differential bracket to crossmember.
Last edited by MelWff; Nov 10, 2022 at 02:22 PM.
Melting Slicks
Joined: Nov 2006
Posts: 3,382
Likes: 1,801
From: Apple Valley, MN
All good advice. I would start with the differential front mount (some refer it to as a “snubber”). Very common to have the type of noise you describe from a badly deteriorated rubber bushing ( there is actually two of them). If you can, get the car up on a hoist and get a breaker bar to assist in seeing how much movement (up and down) there is in that connection.
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Advanced
Joined: Dec 2020
Posts: 70
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From: Babson Park Florida
A Positive Update!
I got around to putting the 71 C3 on jacks Sunday afternoon (It was a beautiful Central Florida day) to see if I could figure out the “clunk” noise. Much to my surprise I found the drive and pinion U Joints to be in very good condition.
While up in the air I moved into changing oil, radiator and differential fluids, then proceeded to check for and tighten loose bolts, and tighten and tighten and tighten. It was astonishing how much loose hardware was going on!
When I got to the front of the car, I found the two end links were extremely loose with worn out bushings. Changing these out will be my next “Corvette list” project.
A test drive revealed the “clunk” noise has been eliminated! I figure it was either sloppy front-end links which I temporally tightened or the differential fluid that did the trick.
At any rate “clunk” is resolved and I must say I’m proud of myself!
Alan
While up in the air I moved into changing oil, radiator and differential fluids, then proceeded to check for and tighten loose bolts, and tighten and tighten and tighten. It was astonishing how much loose hardware was going on!
When I got to the front of the car, I found the two end links were extremely loose with worn out bushings. Changing these out will be my next “Corvette list” project.
A test drive revealed the “clunk” noise has been eliminated! I figure it was either sloppy front-end links which I temporally tightened or the differential fluid that did the trick.
At any rate “clunk” is resolved and I must say I’m proud of myself!
Alan
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Safety Car
Joined: May 2001
Posts: 4,741
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From: Fairfax Virginia
It is great that you solved the clunk you had!
I would still check the trailing arms as they can and do wear out. Mine were shot when I bought my C3 and I didn't know it until it rained one day while I was out in my Corvette. I then learned first hand how to drive a car in a straight line with the rear wheels tracking on their own. The car was absolutely dangerous and I should have caught it before I had my wife in the car with me in the rain. It is fairly easy to find when you jack up the rear and try moving the rear wheels on top and the bottom. If the rear wheel bearings go too far they can cut into the axle which could make you a three wheeled Corvette. I hope you enjoy and de-stress for many many years in your 1973 C3!
After buying my 1968 C3 I replaced all the ball joints, tie rods and bushings in the front end as well as overhauled the entire rear suspension and entire brake system. It had almost 70k miles on it being 24 years old I just felt I would feel safer on a car that I could trust. I love my C3!
I would still check the trailing arms as they can and do wear out. Mine were shot when I bought my C3 and I didn't know it until it rained one day while I was out in my Corvette. I then learned first hand how to drive a car in a straight line with the rear wheels tracking on their own. The car was absolutely dangerous and I should have caught it before I had my wife in the car with me in the rain. It is fairly easy to find when you jack up the rear and try moving the rear wheels on top and the bottom. If the rear wheel bearings go too far they can cut into the axle which could make you a three wheeled Corvette. I hope you enjoy and de-stress for many many years in your 1973 C3!
After buying my 1968 C3 I replaced all the ball joints, tie rods and bushings in the front end as well as overhauled the entire rear suspension and entire brake system. It had almost 70k miles on it being 24 years old I just felt I would feel safer on a car that I could trust. I love my C3!
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
I got around to putting the 71 C3 on jacks Sunday afternoon (It was a beautiful Central Florida day) to see if I could figure out the “clunk” noise. Much to my surprise I found the drive and pinion U Joints to be in very good condition.
While up in the air I moved into changing oil, radiator and differential fluids, then proceeded to check for and tighten loose bolts, and tighten and tighten and tighten. It was astonishing how much loose hardware was going on!
When I got to the front of the car, I found the two end links were extremely loose with worn out bushings. Changing these out will be my next “Corvette list” project.
A test drive revealed the “clunk” noise has been eliminated! I figure it was either sloppy front-end links which I temporally tightened or the differential fluid that did the trick.
At any rate “clunk” is resolved and I must say I’m proud of myself!
Alan
While up in the air I moved into changing oil, radiator and differential fluids, then proceeded to check for and tighten loose bolts, and tighten and tighten and tighten. It was astonishing how much loose hardware was going on!
When I got to the front of the car, I found the two end links were extremely loose with worn out bushings. Changing these out will be my next “Corvette list” project.
A test drive revealed the “clunk” noise has been eliminated! I figure it was either sloppy front-end links which I temporally tightened or the differential fluid that did the trick.
At any rate “clunk” is resolved and I must say I’m proud of myself!
Alan
You da man!!!
Le Mans Master
Joined: Aug 2005
Posts: 6,513
Likes: 1,949
From: Temple Terrace Florida
Alan: The NCRS winter meet has been ongoing for decades. It has been held in Cypress Gardens, now Lago Land, the Orlando sports Center, Old Town in Kissimmee and now at the Lakeland regional airport. Do a Google search for the 2023 meet. The meet used to be gigantic with hundreds of cars and venders. The past few years, it has grown smaller. It usually held in late January or early February. Jerry