need help diagnosing a problem....
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 829
Likes: 131
From: Spartanburg SC
need help diagnosing a problem....
Took my 72 for a ride tonight. As soon as I pulled out of the drive I had a popping sound from the left rear of the car when going in a straight line. It felt like something was hitting the underside of the car with every rotation of the tire. Stopped and checked that something wasn't stuck in the tire. Turned around and took her home. Made a right turn and it sounded like the exhaust was dragging on the pavement. It's not. Major grind/rattling noise. No noise when turning left. Jacked car up, no play on wheel at the 3 and 9 position. Does have a quarter inch play in the 12 and 6 position.
Does this sound like the diff? Does the play on the tire indicate bad u-joints? I understand that play at the 3 and 9 means wheel bearings and play at the 12 and 6 indicates u-joints.
I've owned this car for 40 years, so nothing has been replaced back there.
Does this sound like the diff? Does the play on the tire indicate bad u-joints? I understand that play at the 3 and 9 means wheel bearings and play at the 12 and 6 indicates u-joints.
I've owned this car for 40 years, so nothing has been replaced back there.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,333
From: North of Toronto - Ontario
Noise from the rear diff while going straight is more unusual that while turning one way or the other and the clutches etc are working.
Does the noise go away or change while coasting (actually in neutral) as compared with in drive (in gear and under load)
Hard to say without more info but if I had to place a random wild guess I'd go with something in the parking brake mechanism has let go and is hanging up inside the rotor.
HIH
M
Does the noise go away or change while coasting (actually in neutral) as compared with in drive (in gear and under load)
Hard to say without more info but if I had to place a random wild guess I'd go with something in the parking brake mechanism has let go and is hanging up inside the rotor.
HIH
M
CF Community Team
Joined: Oct 2004
Posts: 19,341
Likes: 5,232
From: Cape Cod, Mass.
2025 C6 of the Year Finalist - Unmodified
2025 C8 Z06/7/E-Ray of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2021 C8 of the Year Finalist Unmodified
2020 Corvette of the Year Finalist (performance mods)
2019 C1 of Year Winner (performance mods)
2017 Corvette of the Year Finalist
2016 C2 of Year
2015 C3 of Year Finalist
If it's not the parking brake, you might consider changing your rear diff fluid and adding a 4 oz bottle of GM posi lube. I've heard alot of grinding noises from the rear end corrected with a simple fluid change and some figure 8's in a parking lot to work it into the clutches.
Racer
Joined: Apr 2008
Posts: 406
Likes: 46
From: Lebanon OH
Generally, you know you need diff additive if the popping occurs when your making a turn. This is because the clutches rub against each other in a turn as each rotates a different speed to allow the inner tire to move slower while still delivering drive power. In a straight line, the clutches should move together as a unit and I would expect any popping to come from a different source.
The u-joint attaches to the bearing assembly via the flange. Since your tire has no movement at 3 and 9, the bearing is probably good and the u-joint seems like the likely culprit.
I had a u-joint fail with no warning on the wheel side of the half shaft. When I pushed in the clutch to take the pressure off, it made a hell of racket in sync with the tire rotation. When I took it apart, it was bone dry. That's what I would look at first.
The u-joint attaches to the bearing assembly via the flange. Since your tire has no movement at 3 and 9, the bearing is probably good and the u-joint seems like the likely culprit.
I had a u-joint fail with no warning on the wheel side of the half shaft. When I pushed in the clutch to take the pressure off, it made a hell of racket in sync with the tire rotation. When I took it apart, it was bone dry. That's what I would look at first.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 829
Likes: 131
From: Spartanburg SC
Thanks to all three of you for your replies. I had already decided to change the diff fluid, it's cheap and easy, but, I only have about 2000 miles on the last change. I am assuming that is not the problem.
I'm going to pull the wheel and rotor to check the emerg. brakes. I'm not sure how to tell if the u-joint is bad. I guess I'll check for looseness etc.
I'm going to pull the wheel and rotor to check the emerg. brakes. I'm not sure how to tell if the u-joint is bad. I guess I'll check for looseness etc.
Le Mans Master
Joined: May 2007
Posts: 5,007
Likes: 1,114
From: North tonawanda NY
Thanks to all three of you for your replies. I had already decided to change the diff fluid, it's cheap and easy, but, I only have about 2000 miles on the last change. I am assuming that is not the problem.
I'm going to pull the wheel and rotor to check the emerg. brakes. I'm not sure how to tell if the u-joint is bad. I guess I'll check for looseness etc.
I'm going to pull the wheel and rotor to check the emerg. brakes. I'm not sure how to tell if the u-joint is bad. I guess I'll check for looseness etc.
Was the plug installed correctly and
Did they add the posi slip additive?
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
With the car in the air, have someone grab the tire at 12 and 6 and move it that 1/4" while you look at the U-joints and half shaft to see what is moving. If there is play in a U-joint, you should be able to see it. If the wheel/tire is moving, but the trailing arm isn't, it could very well be a wheel bearing.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 829
Likes: 131
From: Spartanburg SC
I did use the posi fluid, but, this time I used a product from NAPA called TransX that is supposedly equivalent to the GM fluid. I'm going back to the GM product.
Thanks for your input.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 829
Likes: 131
From: Spartanburg SC
With the car in the air, have someone grab the tire at 12 and 6 and move it that 1/4" while you look at the U-joints and half shaft to see what is moving. If there is play in a U-joint, you should be able to see it. If the wheel/tire is moving, but the trailing arm isn't, it could very well be a wheel bearing.
Burning Brakes
Joined: Oct 2001
Posts: 911
Likes: 5
From: TN
40 years
Took my 72 for a ride tonight. As soon as I pulled out of the drive I had a popping sound from the left rear of the car when going in a straight line. It felt like something was hitting the underside of the car with every rotation of the tire. Stopped and checked that something wasn't stuck in the tire. Turned around and took her home. Made a right turn and it sounded like the exhaust was dragging on the pavement. It's not. Major grind/rattling noise. No noise when turning left. Jacked car up, no play on wheel at the 3 and 9 position. Does have a quarter inch play in the 12 and 6 position.
Does this sound like the diff? Does the play on the tire indicate bad u-joints? I understand that play at the 3 and 9 means wheel bearings and play at the 12 and 6 indicates u-joints.
I've owned this car for 40 years, so nothing has been replaced back there.
Does this sound like the diff? Does the play on the tire indicate bad u-joints? I understand that play at the 3 and 9 means wheel bearings and play at the 12 and 6 indicates u-joints.
I've owned this car for 40 years, so nothing has been replaced back there.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 829
Likes: 131
From: Spartanburg SC
Since you stated you have owned your Corvette for 40 years, how much mileage has accumulated? I have owned my 1970 for 44 years and the rear wheel bearings have been serviced 3 times. The second time it was done the drivers side wheel actually locked up and would not turn and was serviced by a experienced Corvette mechanic. I did the wheel bearings the third time. If you have the money suggest you send yours to BAIRS and get a professional rebuild that is guaranteed.
Racer
Joined: Apr 2008
Posts: 406
Likes: 46
From: Lebanon OH
Thanks to all three of you for your replies. I had already decided to change the diff fluid, it's cheap and easy, but, I only have about 2000 miles on the last change. I am assuming that is not the problem.
I'm going to pull the wheel and rotor to check the emerg. brakes. I'm not sure how to tell if the u-joint is bad. I guess I'll check for looseness etc.
I'm going to pull the wheel and rotor to check the emerg. brakes. I'm not sure how to tell if the u-joint is bad. I guess I'll check for looseness etc.
Checking the wheel at 12 and 6 causes the force to be applied on a plane perpendicular to the trailing arm, which causes the trailing arm to want to rotate at the bushing. It also wants to rotate at the halfshaft connection, or flange. If the tire is tight at 3 and 9, and loose at 12 and 6, I would still think the problem is the u-joint. If you have a helper, they can watch while you move the wheel.