Vibration at specific RPM

[cstaup]

I have this annoying vibration as the RPMs increase at about 18mph in first 30 mph in second and so on.

This doesn't happen as I depress the clutch, and rev it up, just when I'm moving. That means I've eliminated an out of balance flywheel. Has anybody seen out of balance clutch discs?

[rickf]

It could be but what you are describing is common on 151's. It is the engine but you are just not hitting the particular rpm long enough when free revving it. That being said I did get a NOS flywheel not long ago that had the holes drilled off center by .006. That would give a vibration. Did you just put a new flywheel on and by any chance were the bolts a little snug?

Rick

[cstaup]

Rick, I used the "old" flywheel with a new bearing. I'll gun it for a longer period as well as running it in neutral (as that would turn the clutch as well. Thanks.

Chris

[rickf]

Chris, I just looked at the speeds and the gears listed. You must be screaming that thing! There is no need to rev it that high. I start in second and I probably shift into third at around 25 I would guess. I don't watch the speedo but I am not screaming it when I shift and it pulls hard at low rpm.

Rick

[muttguru]

I have this annoying vibration as the RPMs increase at about 18mph in first 30 mph in second and so on.
This doesn't happen as I depress the clutch, and rev it up, just when I'm moving. That means I've eliminated an out of balance flywheel. Has anybody seen out of balance clutch discs?

Chris, just a thought....if you've changed the clutch, then you've had the engine out. If you've had the engine out, you've disconnected the exhaust system. Sometimes, the exhaust can vibrate because it is fixed to the body and not "suspended" like regular auto exhausts. Did you slacken/adjust all the clamps AFTER the engine went back in?

If you try everything else and it still doesn't cure the problem, get under the vehicle and slacken all the clamps for the exhaust system and then re-tighten, taking care to realign the system as necessary.

[cstaup]

Chris, I just looked at the speeds and the gears listed. You must be screaming that thing! There is no need to rev it that high. I start in second and I probably shift into third at around 25 I would guess. I don't watch the speedo but I am not screaming it when I shift and it pulls hard at low rpm.

Rick

You're right Rick. I just used those speeds as a reference. I don't push it to 30 in second. I generally shift up when it "feels" right, that is when I am out of the "power band" If I go past that is when all the shaking starts.

Ken, I have replaced the entire exhaust system with NOS. I'll loosen it all and reposition, making sure that there is sufficient clearance.

I will report back. Thanks all.

Chris