L-82 has vibration
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
L-82 has vibration
Hey guys. I just acquired another Corvette, a 1976 L-82. Matching numbers car that runs and drives great. No unusual noises, no smoke, no blow-by and holds good oil pressure. However, it has a fairly noticeable vibration. It seems to intensify as the RPMs increase. It does it sitting still idling or cruising down the road. Same vibration with clutch in or out.
It has new motor mounts. new transmission mounts and a new clutch, (all done by the previous owner...probably chasing down the same vibration).
Any ideas what could cause a vibration like I described?
I'm "assuming" it's in the motor or transmission.
It has new motor mounts. new transmission mounts and a new clutch, (all done by the previous owner...probably chasing down the same vibration).
Any ideas what could cause a vibration like I described?
I'm "assuming" it's in the motor or transmission.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
The car doesn't have a miss-fire. It runs great...other than the vibration. It's firing well on all cylinders with perfect compression on all cylinders...each within 5lbs of each other.
Melting Slicks
Joined: May 2006
Posts: 2,369
Likes: 103
From: Centerville Louisiana
I have one with a vibration issue in the 3k range. I've replaced the usual suspects and, I gave up. Hoping it will break and I can fix it. I really think it's in the back somewhere.
Racer
Joined: Jun 2016
Posts: 336
Likes: 29
From: Il.
When I pulled the engine out of my 77 after I made the decision to rebuild it,I found the rubber in the vibration damper was dry rotted . Might want to check the one you have that could be causing you're vibration.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
I am starting to think that my vibration may be because of a bad harmonic balancer.
Is there any way to check before I pull it down?
Also, can I replace the harmonic balancer with the engine in the car?
Is there any way to check before I pull it down?
Also, can I replace the harmonic balancer with the engine in the car?
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Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Just curious. Does the harmonic balancer appear to be spinning true? Or is there a slight wobble? Some of those old units tend to seperate, meaning the outer shell slips from the inner. Replacement isn't that bad a job:
Loosen A/C, P.S. and Alt so as to remove belts. But first, take a piece of masking tape and label each belt in order of removal and intial it for future location. Next using a boxend wrench remove fan, clutch, pulley. Now you have access to remove vibration damper bolt with torque wrench, slowly. You DO NOT want that to snap off! Now you can use a puller. In some cases the fan shroud will have to come out, not an easy task, but do-able.
Loosen A/C, P.S. and Alt so as to remove belts. But first, take a piece of masking tape and label each belt in order of removal and intial it for future location. Next using a boxend wrench remove fan, clutch, pulley. Now you have access to remove vibration damper bolt with torque wrench, slowly. You DO NOT want that to snap off! Now you can use a puller. In some cases the fan shroud will have to come out, not an easy task, but do-able.
Last edited by HeadsU.P.; Nov 23, 2017 at 09:44 AM.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
To answer a couple of questions:
it does not have a fan or fan clutch. It has been upgraded to electric fans on the aluminum radiator.
The harmonic balancer appears to be running smooth and true with no visible wobble.
i have found the exhaust pipe hitting the opening in the frame. Could something that simple cause an entire car vibration?
it does not have a fan or fan clutch. It has been upgraded to electric fans on the aluminum radiator.
The harmonic balancer appears to be running smooth and true with no visible wobble.
i have found the exhaust pipe hitting the opening in the frame. Could something that simple cause an entire car vibration?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Ahh. It will be wise for me refresh my memory from the first post.
Ok, so the drivetrain is out.
How about that clutch that was installed by the former owner? Can you get a good visual on that? No. Only thing I can think of is a flywheel that was not installed correctly or maybe warped? I assume a locator pin was on the end of the crank to align the flywheel correctly? Maybe a flywheel bolt came loose? Maybe a clutch bolt came off? Did someone use LocTite on the bolts? IDK. You can't see anything going on with those one piece bellhousings.
Ok, so the drivetrain is out.
How about that clutch that was installed by the former owner? Can you get a good visual on that? No. Only thing I can think of is a flywheel that was not installed correctly or maybe warped? I assume a locator pin was on the end of the crank to align the flywheel correctly? Maybe a flywheel bolt came loose? Maybe a clutch bolt came off? Did someone use LocTite on the bolts? IDK. You can't see anything going on with those one piece bellhousings.
Last edited by HeadsU.P.; Nov 23, 2017 at 05:39 PM.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
Ahh. It will be wise for me refresh my memory from the first post.
Ok, so the drivetrain is out.
How about that clutch that was installed by the former owner? Can you get a good visual on those? No. Only thing I can think of is a flywheel that was not installed correctly or maybe warped? I assume a locator pin was on the end of the crank to align the flywheel correctly? Maybe a flywheel bolt came loose? Maybe a clutch bolt came off? Did someone use LocTite on the bolts? IDK. You can't see anything going on with those one piece bellhousings.
Ok, so the drivetrain is out.
How about that clutch that was installed by the former owner? Can you get a good visual on those? No. Only thing I can think of is a flywheel that was not installed correctly or maybe warped? I assume a locator pin was on the end of the crank to align the flywheel correctly? Maybe a flywheel bolt came loose? Maybe a clutch bolt came off? Did someone use LocTite on the bolts? IDK. You can't see anything going on with those one piece bellhousings.
Instructor
Joined: Jun 2017
Posts: 153
Likes: 18
From: New Jersey
I recently helped a friend chase down a vibration in his 396
He mentioned the balancer, so I said to him well you've changed your belts in those 50,000 miles in your 50 year old car right? So why would you think the rubber in the balancer was not in need of checking?
We sent the Harmonic balancer to "The Damper Doctor" He reconditioned it and turned out real nice. But that did not fix it.
In any event, It turned out when the flywheel was cut the machine shop rookie cut it warped. Ended up resufacing it again. Well long story short he ended up with a brand new flywheel and now smooth as can be.
He mentioned the balancer, so I said to him well you've changed your belts in those 50,000 miles in your 50 year old car right? So why would you think the rubber in the balancer was not in need of checking?
We sent the Harmonic balancer to "The Damper Doctor" He reconditioned it and turned out real nice. But that did not fix it.
In any event, It turned out when the flywheel was cut the machine shop rookie cut it warped. Ended up resufacing it again. Well long story short he ended up with a brand new flywheel and now smooth as can be.
Racer
Joined: Nov 2017
Posts: 289
Likes: 32
#5 And #7 Spark Plug Wires Crossed?
I would check the #5 and #7 spark plug wires to see if the previous owner crossed them. If they did get crossed the #5 cylinder would fire 90 degrees too late and the #7 cylinder would fire 90 degrees too early. And that WOULD cause a noticeable vibration at idle as well as at higher rpm's.