Driveline Vibration

[cdowns]

some vendors sell the angle shims cheaply that go under the saddles

another thing to check is make sure the drivshaft tyoke isnt going too far into the tranny// when i lowered 4" i trimmed about 3/8" off the yoke to b sure

[jholley]

Thanks. How did you trim it? On a band saw?

Originally Posted by cdowns

some vendors sell the angle shims cheaply that go under the saddles

another thing to check is make sure the drivshaft tyoke isnt going too far into the tranny// when i lowered 4" i trimmed about 3/8" off the yoke to b sure

[DANTIP]

Just curious, does the vibration go away in neutral?

[jholley]

Originally Posted by DANTIP

Just curious, does the vibration go away in neutral?

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.

After looking at a buddies trucks (3) and seeing how much his slip yoke was sticking out of the trans tailshaft (about 5/8" - 3/4") I'm pretty sure that mine is either bottoming out or close to it. I don't have any stickout whatsoever. I took it back over to the driveshaft shop to get shortened about 5/8" and have a brand new slip yoke put on it just to be sure that isn't the problem.

Cdowns, will it bottom out on the inside or the outside of the slip yoke? And just out of curiousity are there any shims or washers in between where the shafts bolt together?

[Keith Seymore]

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.

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

[cdowns]

Originally Posted by jholley

Thanks. How did you trim it? On a band saw?

just used a chop saw with a fiber cutoff blade then dressed the cut with a good file