Robert H

I have a 70 Corvette, 454, manual trans with a vibration that seems to be from the engine. The vibration starts in about 2100 rpm and ends above 2600 rpm. The vibration occurs moving in all gears, or standing still. Standing still it occurs with the car in neutral, clutch out, or in gear with the clutch pushed in. The last case takes everything out of the equation except the engine, pressure plate and accessories. The engine was rebuilt some time ago and supposedly the internals were balanced at that time. I believe the vibration damper was replaced at that time also, but I don't remember for sure (it has been many years ago). I have tried looking at the engine while it is running at the rpm in question, but don't see anything shaking. This is not a serious vibration, but it is noticeable, and is something I have always wondered about, and would like to fix if possible. Could a defective vibration damper do this? Any ideas would be appreciated.

TimAT

IF this just started, I'd look at the balancer and see if it is failing and has slipped. IF not, what was the last thing done to the engine before it started? Try removing the belts and running it. IT could be the fan or an accessory too.

flyeri

Always wondered about? When I replaced the clutch in mine I found that the pressure plate did not have shouldered bolts. The slight vibration I had went away when the correct bolts were installed and the pressure plate was centered up correctly.

Vibguy

If the problem has been there forever it is probably not this but my previous vibration issues on other vehicles always turned out to be motor mount related. It might be worth taking a peek at yours.

MelWff

assuming you have a clutch on the fan, grab two opposite fan blades and see if there is excessive play in the clutch bearing.

7T1vette

The source of that vibration is in one of the following:

1. the engine itself....moving components balance problem;

2. the vibration damper at the front of the crank;

3. the radiator fan;

4. one (or more) of the components driven by fan belts;

5. the pressure plate/clutch (not centered).

You can eliminate #3 and #4 by removing all of the drive belts and revving the engine to see if the vibration is still there. Running the engine for a minute or so without the water pump running is no big deal.

There is no good way to separate out the potential problems with the damper, the clutch, nor the internal balance. But, thinking about WHEN this became a problem my help eliminate one or more of those items. If the vibration wasn't a problem before you did some specific work on the engine, use that as a clue. Likewise, if the vibration REMAINED after doing some specific work on the engine, that would also be a useful clue toward diagnosing the problem source.

Jims66

If the motor has been rebuilt before you owned it..., and it's always done it since you've owned it, maybe the wrong balancer (or flywheel) was used ? 454s are externally balanced motors (vice internally balanced 396s and 427s). Just a thought....

7T1vette

My bet is on a non-centered pressure plate and disc. It doesn't have to be off much to make a lot of vibration.

Defective or wrong damper would be my second choice.

Robert H

Thanks to all for the ideas. Gives me a place to start.