Quote:
Originally Posted by jholley
It is significantly reduced when the driveshaft is loaded, either accelerating or decelerating. When I'm cruising and feathering the throttle to maintain a constant speed is when it's the worst. Most of the time above 55-60 though I have a light rhythmic vib.
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Driveline vibrations are often torque sensitive, so the fact that it varies based on load is a good clue, pointing to the driveline.
The light rhythmic vibration is called a "boom/beat", and that means there are two vibrations going on at the same time, canceling and adding in amplitude as they go in and out of phase.
It is very likely the driveline (u joints are a second order of driveline, that is, they give you a "kick" two times for every time the shaft goes around) phasing with engine firing frequency.
1) Does the rhythmic vibration go away if you chose a different gear (while maintaining the same speed)?
2) Did you say what engine you have? V8 firing is four times per rev (4th order), I'd have to check to see what it is for an L6.
K