The Stovebolt Site Forums The Shop Area Engine Shop Vibration just off idle '57 235

I have a '57 Chevrolet 150 with a 235 and factory overdrive. It has a vibration just off of idle that I can't seem to pinpoint. It's fine at idle but just off of idle (my carb throttle shaft is warn and sometimes it idles a little fast until I punch the throttle) and at this faster idle it has a very noticeable vibration. Also, when I wind the car up in 3rd gear to get into overdrive the vibration is very present until I get into overdrive.

My suspicions are: Harmonic Balancer/crank/flywheel. Perhaps even an ignition miss, but I don't think a miss would cause the vibration I'm getting. I forgot to add that the crank and balancer has been drilled so that the balancer can be bolted on due to the keyway being worn.

What should I do to begin diagnosing this issue?

Thanks,
Brandon

Brandon,

I won't be much help, but I'd check the simple stuff first.

Have you checked the tightness of the motor mounts?
Have you checked all bolts between engine, transmission and rear end?
Are u-joints good?

Good luck,

"I forgot to add that the crank and balancer has been drilled so that the balancer can be bolted on due to the keyway being worn."

Is the worn keyway on the balancer, or the crank, or both? I would start looking there. All the bolt will do is keep the crank from falling off once the balancer has been installed with an installer tool. It may hold it on straight, or anything but straight if the balancer and/or crank snout is goobered up.
Carl

when did this problem start? any work done to this car prior to the vibration? could it be in the drive shaft or a motor mount.

Start with checking plug wires, make sure the carb is adjusted right.points and condenser can cause problems.compression test can tell you a lot as well.always eliminate the basics first. Any of the above will cause issues when engine is under load.

Thanks for the suggestions. I'll check on these and go from there.

I can't remember exactly when this started, because the car had been put up for about 3 years. I don't remember this being an issue when I put it up, but I cannot say for certain.

I did install a new clutch and had the flywheel turned prior to getting the car ready for the road again. The previous clutch had been soaked by a rear main leak and would shudder when it got up to operating temp. Turning the flywheel and new clutch fixed that problem. Could this have anything to do with it? The flywheel will only install one way.

A stupid question which I hesitate to ask. Did you fix the leaky rear main seal?

Yep, I did

Will it get rough off idle while in neutral? Or just when driving.?

Both. Because the shaft is warn on the carb it sometimes sticks at redlights and idles a bit higher than actual idle. It has the vibration pretty bad at this time. I can punch the throttle and it causes the car to idle normally, and the vibration isn't bad. When I build rpm and I'm about to change gears, it's pretty bad and if I'm in 3rd gear on the highway it's can be bad until I shift into overdrive. In overdrive on the highway, it's not bad at all.