Shaking
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
Shaking
My 76 is shaking, bouncing, whatever you want to call it. The faster I go the worse it gets. And I feel like it's the front but not 100% sure. It's not the tires / rims. I've had them checked by two different places. I know it could be a few things but is there something that would be more common for me to check out?
Race Director
Joined: Mar 2017
Posts: 11,949
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From: Virginia
I'd still guess wheels/tires before anything else. What's the date code on the tires?
If you have a square set, rotate them front to back, and side, to side. If the symptoms don't change, I'll shut up.
If you have a square set, rotate them front to back, and side, to side. If the symptoms don't change, I'll shut up.
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
So, I put brand new tires and two new rims. Took it back to the dealer that sold me the tires and they balanced them again. No change. But I was still thinking (hoping) it was tires or rim. So, I swapped out one at a time with a spare that I made sure was balanced. No change. Then took the car to Discount Tires where they do a road force balancing. No change. That's where I'm at. Guess I'll take it to a shop in the near future.
Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
Haven't had the car long and I swear it did not do this with the 15 year old tires that were on the car.
So, I put brand new tires and two new rims. Took it back to the dealer that sold me the tires and they balanced them again. No change. But I was still thinking (hoping) it was tires or rim. So, I swapped out one at a time with a spare that I made sure was balanced. No change. Then took the car to Discount Tires where they do a road force balancing. No change. That's where I'm at. Guess I'll take it to a shop in the near future.
So, I put brand new tires and two new rims. Took it back to the dealer that sold me the tires and they balanced them again. No change. But I was still thinking (hoping) it was tires or rim. So, I swapped out one at a time with a spare that I made sure was balanced. No change. Then took the car to Discount Tires where they do a road force balancing. No change. That's where I'm at. Guess I'll take it to a shop in the near future.
I'd look for worn ball joints, bad bushings (trailing arms and strut rods), or even a cracked frame (near the steering box, perhaps).
Is the shaking RPM dependent? If you engage the clutch, or put the car in Neutral, does the shaking go away?
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Mine did the same thing about 2 years ago. Front end would shake so bad I thought the fenders would crack right off the car! I never did run a thread on it. But it was discussed on the "What did you do to your C3 today " thread for over 6 months.
I ended up completely rebuilding absolutely everything under the car. Every ball joint, every tie rod end, idler arm, steering box, shock, U joint, wheel bearing, absolutely everything! And still it shook.
had the drive shaft rebalanced twice, Finally in absolute desperation, took the half shafts in to have them balanced. Yes had changed all U joints a few months earlier. Found the joints of the half shafts twisted. Only found that by spinning on the balance machine. Yes rebuilt the rear spindles, you name it. I was going mad and broke. New half shafts later. And finally it was fixed.
for 46 years it didn't shake. Then. It did and I couldn't find it or even pin point where its was coming from. I feel your pain.
Best of luck finding it.
I ended up completely rebuilding absolutely everything under the car. Every ball joint, every tie rod end, idler arm, steering box, shock, U joint, wheel bearing, absolutely everything! And still it shook.
had the drive shaft rebalanced twice, Finally in absolute desperation, took the half shafts in to have them balanced. Yes had changed all U joints a few months earlier. Found the joints of the half shafts twisted. Only found that by spinning on the balance machine. Yes rebuilt the rear spindles, you name it. I was going mad and broke. New half shafts later. And finally it was fixed.
for 46 years it didn't shake. Then. It did and I couldn't find it or even pin point where its was coming from. I feel your pain.
Best of luck finding it.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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You need to be methodical....what speed does it start at, is it rpm dependant, same speed but different gears, get worse in a turn, any loud clunking when taking off from a stop?
Lots of things can do this as everyone stated
Ball joints, tie rod ends, idler arm, loose steering connections.
Broken motor mounts, tranny mounts, rear differential snubbers, u joints, ya got 6....loose traling arms, loose connecting arms....
I would start logging the pertinent info. Then go to each tire and yank on it to see if anything is loose, then jack up each tire and do it again rocking the top and bottom then left and right....get underneath and spin the shafts although you need to support the rear trailing arms so the half shafts joints dont bind
Lots of things can do this as everyone stated
Ball joints, tie rod ends, idler arm, loose steering connections.
Broken motor mounts, tranny mounts, rear differential snubbers, u joints, ya got 6....loose traling arms, loose connecting arms....
I would start logging the pertinent info. Then go to each tire and yank on it to see if anything is loose, then jack up each tire and do it again rocking the top and bottom then left and right....get underneath and spin the shafts although you need to support the rear trailing arms so the half shafts joints dont bind
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Pro
Joined: May 2019
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From: Fountain Hills (Phoenix) AZ
What brand of tires?
When I bought my '75 coupe last year, the PO had installed new "Phantom" brand tires as the car had sat unused for many years. The local tire shop uses a "road force" balancing technique and claimed the tires were balanced. After a couple of trips to the local shop, due to front end shake, I asked the guys there to put the wheels/tires on the balance machine and just spin for runout/true check. All tires were 1/16" or more out of round. Cheap tires. Replaced with BFG's and the car drives smooth as glass.
When I bought my '75 coupe last year, the PO had installed new "Phantom" brand tires as the car had sat unused for many years. The local tire shop uses a "road force" balancing technique and claimed the tires were balanced. After a couple of trips to the local shop, due to front end shake, I asked the guys there to put the wheels/tires on the balance machine and just spin for runout/true check. All tires were 1/16" or more out of round. Cheap tires. Replaced with BFG's and the car drives smooth as glass.
Melting Slicks
Joined: Oct 2003
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From: Chapel Hill NC
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What perplexes me is that you didn't have the problem until you put on new tires and rims. Coincidence?
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
You need to be methodical....what speed does it start at, is it rpm dependant, same speed but different gears, get worse in a turn, any loud clunking when taking off from a stop?
Lots of things can do this as everyone stated
Ball joints, tie rod ends, idler arm, loose steering connections.
Broken motor mounts, tranny mounts, rear differential snubbers, u joints, ya got 6....loose traling arms, loose connecting arms....
I would start logging the pertinent info. Then go to each tire and yank on it to see if anything is loose, then jack up each tire and do it again rocking the top and bottom then left and right....get underneath and spin the shafts although you need to support the rear trailing arms so the half shafts joints dont bind
Lots of things can do this as everyone stated
Ball joints, tie rod ends, idler arm, loose steering connections.
Broken motor mounts, tranny mounts, rear differential snubbers, u joints, ya got 6....loose traling arms, loose connecting arms....
I would start logging the pertinent info. Then go to each tire and yank on it to see if anything is loose, then jack up each tire and do it again rocking the top and bottom then left and right....get underneath and spin the shafts although you need to support the rear trailing arms so the half shafts joints dont bind
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
What brand of tires?
When I bought my '75 coupe last year, the PO had installed new "Phantom" brand tires as the car had sat unused for many years. The local tire shop uses a "road force" balancing technique and claimed the tires were balanced. After a couple of trips to the local shop, due to front end shake, I asked the guys there to put the wheels/tires on the balance machine and just spin for runout/true check. All tires were 1/16" or more out of round. Cheap tires. Replaced with BFG's and the car drives smooth as glass.
When I bought my '75 coupe last year, the PO had installed new "Phantom" brand tires as the car had sat unused for many years. The local tire shop uses a "road force" balancing technique and claimed the tires were balanced. After a couple of trips to the local shop, due to front end shake, I asked the guys there to put the wheels/tires on the balance machine and just spin for runout/true check. All tires were 1/16" or more out of round. Cheap tires. Replaced with BFG's and the car drives smooth as glass.
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,209
Likes: 9,348
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
If it does it as soon as you are rolling Im sure it will be obvious to the trained eye....they will get it straightenned out for you
Drifting
Joined: Apr 2004
Posts: 1,422
Likes: 127
From: Mequon WI
Seems you have ruled out the wheels and tires. Car is 50 years old and all those suspension joints and rubber parts have arthritis. You are driving it a lot compared to previous owners and that old stuff can’t keep up anymore. Going through the same with my 78.
if the shaking / vibration happens under load it most likely is one or all of the 6 u joints.
if you feel it through the steering wheel I would start with front suspension parts. Control arm bushings and ball joints were my problem. To replace control arm bushings requires complete disassembly. During reassembly replace ball joints tie rod ends etc .
in my case after front end rebuil car is still “squarely”. To the point I can’t drive it. Currently removing the trailing arms and differential for professional rebuild. Not unusual for TA bushings to were out. My car has at least 110k miles, so there is that wear factor which you might not have.
Please keep this up as you work this through. Really interested in how you get it all fixed.
if the shaking / vibration happens under load it most likely is one or all of the 6 u joints.
if you feel it through the steering wheel I would start with front suspension parts. Control arm bushings and ball joints were my problem. To replace control arm bushings requires complete disassembly. During reassembly replace ball joints tie rod ends etc .
in my case after front end rebuil car is still “squarely”. To the point I can’t drive it. Currently removing the trailing arms and differential for professional rebuild. Not unusual for TA bushings to were out. My car has at least 110k miles, so there is that wear factor which you might not have.
Please keep this up as you work this through. Really interested in how you get it all fixed.
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
Seems you have ruled out the wheels and tires. Car is 50 years old and all those suspension joints and rubber parts have arthritis. You are driving it a lot compared to previous owners and that old stuff can’t keep up anymore. Going through the same with my 78.
if the shaking / vibration happens under load it most likely is one or all of the 6 u joints.
if you feel it through the steering wheel I would start with front suspension parts. Control arm bushings and ball joints were my problem. To replace control arm bushings requires complete disassembly. During reassembly replace ball joints tie rod ends etc .
in my case after front end rebuil car is still “squarely”. To the point I can’t drive it. Currently removing the trailing arms and differential for professional rebuild. Not unusual for TA bushings to were out. My car has at least 110k miles, so there is that wear factor which you might not have.
Please keep this up as you work this through. Really interested in how you get it all fixed.
if the shaking / vibration happens under load it most likely is one or all of the 6 u joints.
if you feel it through the steering wheel I would start with front suspension parts. Control arm bushings and ball joints were my problem. To replace control arm bushings requires complete disassembly. During reassembly replace ball joints tie rod ends etc .
in my case after front end rebuil car is still “squarely”. To the point I can’t drive it. Currently removing the trailing arms and differential for professional rebuild. Not unusual for TA bushings to were out. My car has at least 110k miles, so there is that wear factor which you might not have.
Please keep this up as you work this through. Really interested in how you get it all fixed.
Drifting
Joined: Jun 2025
Posts: 1,715
Likes: 597
Seems MY1976 C3 has only two engine choices; both are 350 GEN 1 sbc. Both are truly "internal" aka Neutral balance. BUT If, Repeat IF engine has been replaced; that engine may Not be internal balance.
Although its OE harmonic balancer aka damper is Neutral balanced, perhaps damper's rubber bonding (between outer inertia ring and inner hub) has deteriorated and failed (that often happens w/age). That could permit inertia ring (which IS balanced via several drilled holes AND whose Asymmetrical-locations are drilled when ring & hub are aligned & bonded together) to move axially about crankshaft centerline. And, by ring moving about, damper's balance becomes intermittent. That could cause shaking at any speed.
IF the front balancer aka damper is at fault (they DO fail w/ age), it should be addressed ASAP. It's relatively cheap & easy to R&R. Lotsa DIYers have done job in a few hours or less. The job requires a special remove-install tool; which many FLAPS will loan for just a returnable deposit.
Although its OE harmonic balancer aka damper is Neutral balanced, perhaps damper's rubber bonding (between outer inertia ring and inner hub) has deteriorated and failed (that often happens w/age). That could permit inertia ring (which IS balanced via several drilled holes AND whose Asymmetrical-locations are drilled when ring & hub are aligned & bonded together) to move axially about crankshaft centerline. And, by ring moving about, damper's balance becomes intermittent. That could cause shaking at any speed.
IF the front balancer aka damper is at fault (they DO fail w/ age), it should be addressed ASAP. It's relatively cheap & easy to R&R. Lotsa DIYers have done job in a few hours or less. The job requires a special remove-install tool; which many FLAPS will loan for just a returnable deposit.
Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
Perhaps it's not the tires (though that's still my #1 guess).
You also put on new wheels, right? Did you make sure to use hub-centric wheels, or adapters to make them hub centric? Is there a chance that the wheel is not aligned correctly on the hub? The wheel balancer won't notice this issue, it has a cone that centers the wheel.
"Weaving back and forth" in the rear is usually strut rod or trailing arm bushings.
You also put on new wheels, right? Did you make sure to use hub-centric wheels, or adapters to make them hub centric? Is there a chance that the wheel is not aligned correctly on the hub? The wheel balancer won't notice this issue, it has a cone that centers the wheel.
"Weaving back and forth" in the rear is usually strut rod or trailing arm bushings.
Thread Starter
Burning Brakes
Joined: Oct 2012
Posts: 961
Likes: 118
From: Panama City, Florida
Perhaps it's not the tires (though that's still my #1 guess).
You also put on new wheels, right? Did you make sure to use hub-centric wheels, or adapters to make them hub centric? Is there a chance that the wheel is not aligned correctly on the hub? The wheel balancer won't notice this issue, it has a cone that centers the wheel.
"Weaving back and forth" in the rear is usually strut rod or trailing arm bushings.
You also put on new wheels, right? Did you make sure to use hub-centric wheels, or adapters to make them hub centric? Is there a chance that the wheel is not aligned correctly on the hub? The wheel balancer won't notice this issue, it has a cone that centers the wheel.
"Weaving back and forth" in the rear is usually strut rod or trailing arm bushings.
I already had the trailing arm bushings replaced. No more weaving!!!
Thanks.