C2 Vibration when accelerating

[Roger P.]

Hey guys,
I think one of my motor mounts might be shot, but I wanted to get your thoughts. My '65 convertible SB drives great, but if I accelerate hard - usually in 2nd or 3rd gear - I sometimes get a vibration from the front of the car and through the steering wheel. I don't recall ever getting the vibration when accelerating on the highway once I have shifted into 4th gear, nor do I get the vibration starting off in 1st gear. The vibration stops once I start cruising and remove the lead from my foot . The transmission mount and U-joints are only a year old, so I was ruling them out. Any thoughts of what should be checked in addition to the motor mounts? Your opinions are appreciated!

Roger Piper (50141)

[Edward J.]

Re: C2 Vibration when accelerating

Roger the only thing that comes to mind is to check the engine harmonic balancer, take down the road and see about what RPM the vibration starts, then when you come to a stop slowly race the engine in netural til the RPM is matched at the vibration speed.

Also did the axle half shaft joints get replaced? and just for piece of mind check the rear driveshaft joints again.

The motor mount can be gone, but generally what I see is the engine picking up of the mounts and causing the throttle to stick under hard accelaration.vibrations are rare with the mounts, even when theres a problem with the mount.

[Ricky M.]

Re: C2 Vibration when accelerating

Edward,
Thanks for the thought on vibration not being caused by the motor mount. Drove my '63 today and a vibration started when around 50-55 and accelerating. All halfshaft u-joints have just been replaced so I figured either driveshaft u-joints or motor mount. I'll go ahead and do driveshaft joints and see if that solves the problem.

[Michael F.]

Re: C2 Vibration when accelerating

A truck I used own had a vibration coming from the front end. It made the passenger front tire hop under hard acceleration. Turned out to be a crack in the rear end carrier. Harmonic vibrations can do odd things. They can transmit right through the frame.

[Michael B.]

Re: C2 Vibration when accelerating

Check my vibration article in the Winter 2009 Restorer.

[Mark S.]

Re: C2 Vibration when accelerating

Check your rear half shaft u joints and make sure they are fully seated in the yokes.

[Roger P.]

Re: C2 Vibration when accelerating

Edward, Michael, and Michael,
Thank you for your excellent suggestions. My brother has an auto repair shop, so after doing a road test, I will bring it to his shop and have them take a look. I'll probably get to it on Friday afternoon or Saturday morning and will report back with our findings. Michael, I will look up your article in the Winter 2009 Restorer and get some additional ideas before then. If you have the article as a PDF or on a website, please let me know via PM.

Thanks again,
Roger (50141)

[Roger P.]

Re: C2 Vibration when accelerating

Mark,
Thank you for your suggestion, too. I'm sorry for not including you, but I just now saw your post. I recently overhauled the rear suspension on my car, but didn't change the half-shaft U-joints as I was told they were still OK. One mechanic wanted to change them to "non-greased" joints, but said they didn't otherwise require replacement. The driveshaft U-joint, transmission mount, and differential mount were all recently replaced. Also changed the differential seals, half-shaft C-clips, strut rods, leaf spring bolts & bushings, rear shocks, trailing arms, wheel bearings, etc. What did I miss??

Roger (50141)

[Michael B.]

Re: C2 Vibration when accelerating

Roger,

My vibration was on a BB C3 but you said it disapears in 4th gear and that perked my ears. In 4th the slider locks the input shaft to the main shaft and the power is transmitted straight through the transmission. 1,2, & 3 transmits the power down and through the cluster, putting a side load on the input shaft bearing as the input gear and front cluster gear want to seperate.

I lived with my vibration for many years before I found out it was a cracked input shaft bearing race allowing a lot of play in the input shaft and wearing the pilot bushing. The trans has to come out to check but if you're out of guesses it's a possibility.

Mike

[Tony S.]

Re: C2 Vibration when accelerating

Are your tires properly balanced?

[Paul J.]

Re: C2 Vibration when accelerating

Lots of choices, eh Roger? Have your brother check the tie rod ends.

[Michael J.]

Re: C2 Vibration when accelerating

This is an interesting subject. My '66 L79 and my '67 L71 both have vibrations that actually distort the rear view mirror image when accelerating and sometimes just when running along at 70 mph. They also show it when the motors are revved up standing still. I don't feel anything through the steering wheel, but the vibration, though light, is transmitted through the cage. I had been told this was common in C2s, just the state of the art in the '60s of isolating the motor from the frame. Now I am worried something is wrong, is it?

[Wayne M.]

Re: C2 Vibration when accelerating

Check my vibration article in the Winter 2009 Restorer.

Could you verify that copy of the Restorer ? I have it in front of me, and can see nothing related to vibration in Volume 35, #3; Winter 2009.

[Wayne M.]

Re: C2 Vibration when accelerating

Another possibility -- Dealer service bulletin issued to cover vibration during acceleration (but not coasting), in '73-77 Corvettes (might apply to C2's).

"When vibration not corrected by conventional methods, may be caused by the camber angle of the rear wheels" .... "Torque shake can be corrected by readjusting the rear wheel camber to zero degrees from the normal spec of (minus) 1/2 deg, +/- 1/4 deg."

[Roger P.]

Re: C2 Vibration when accelerating

Paul, Anthony, and Wayne,
Thank you for your additional suggestions. You're right Paul, there are a lot of things to check! I had a mechanic friend stop by last night and he checked the harmonic balancer and motor mounts and told me that they looked very good. With the rear suspension being completely overhauled recently (including driveshaft U-joints), and with a new clutch & pressure plate and various transmission bearings & bushings being replaced about 18 months ago (including the tranny & differential mounts), I am ruling out all of those items. With the vibration coming from the front and through the steering wheel, I am setting my focus on the front suspension. As you mentioned Paul, perhaps the tie rod ends or the ball joints as my mechanic friend suggested. I went for a long test ride this morning on I-95 and couldn't get the vibration to happen even one time, nor does it happen revving the engine in the driveway. Since it happens so infrequently, I will basically ignore the issue for now. However, I will purchase a front end rebuild kit and shocks from Eckler's and have my brother's shop R & R the parts during the winter. Hopefully, that will correct the occasional vibration problem that I have experienced during heavy acceleration. Once I change the front end parts, will I have to re-align the front tires? I just had a front & rear alignment done when the rear suspension job was finished (rear camber was set to about -0.38 deg.).

Thanks again for all your help,
Roger (50141)