Troubleshooting a Vibration ?'s

[dznucks]

I have a '69 C-10 with a mostly stock 350 and a 3 -speed column shift. I have developed a vibration that you can slightly feel at idle and gets worse around 1100 rpm, settles out until up around 3000 rpm and above. New plugs and wires and the engine runs good, so i doubt its a cylinder not firing.

the vidration appears to be in the motor or is directly related to motor RPM. it has nothing to do with being in gear and the truck doens't have to be moving.

I pulled the clutch dust cover and turned the motor over while inspecting the clutch assembly. nothing out of the ordinary. i watched the front of the motor while idling at 1100 and the pulleys and balancer appear ok. It kind of feels like its coming from the back of the motor.

the question is what has everyone else found as a root cause for this type of symptom? I really dont know what else to look at other than the internals of the bottom end.

[Bus Ted Knuckle]

how are your motor mounts?

[71tahoe]

I've had a problem when the clutch was engaged and then it goes away when I disengage the clutch. Was missing the input shaft bushing. Also in additon to the motor/bellhousing mounts, check the harmonic balancer.

[larry may]

Originally Posted by Bus Ted Knuckle

how are your motor mounts?

First place to check . Like Ted said

[dznucks]

Motor mounts are about 4-5 years old. Have had issues with the bolts backing out before, i last checked them a couple months ago. I will re check them tonight though.

When i rev the motor from idle, while watching motor, the motor doesn't seem to vibrate so much as the whole truck does.

[RustyParts]

Also check the rubber in your harmonic balancer, it may be separating.

[dznucks]

The motor mounts are good. Just checked all the bolts.
The balancer looks good and i have also just recently triple checked the TDC mark and i know the balancer hasn't spun. So i am assuming its ok. it doesn't appear to have a wobble when the motors running either.