Vibration being felt/heard in car
 

Hey guys, I seem to have an odd problem.

I have a vibration that is drivetrain related. I cannot tell what or where it comes from, because the vibration is not relevant to RPM.

Car currently is a 12a BP 79 SA. From what I can gather, I would assume it is transmission related.

No matter the RPM, every once in a while (I am talking between 1-3 minutes at any RPM range) there is a big vibration. Kind of like a spinning part has too much weight on one side?

It will come and go, but when it comes, it isn't constant. It oscillates. Forgive my poor use of words, but something like

mmmmmmmmmm.......mmmmmmmmmm.......mmmmmmmmmm.....m mmmmmm.....mmmmmmm...mmm...mmm...mmm...mmm...mmmmm mm......mmmmmmm....mmmmmmmmmm.....mmmmmmmmmm......

It comes and goes, with low then high intensity then low again.

The 79 has a poor transmission. I can not shift without grinding gears unless the RPMs match the gear I have selected. Being a first year car, the tailshaft is not a 2 piece design and I will have to rebuild it. I know you can use other transmissions, but looking up the modifications to make it fit through the stock tunnel are vague at best.


Does this sound like a transmission problem? I know nothing about the engine. My guess is the previous owner took it apart and did the port, then put it back together. However, if different rotor weights were used, wrong counterweights, etc, I feel this vibration would be constant...

Well, the fact that it comes and goes in a rhythmic pattern suggests that it's not ONE thing that's vibrating, but several which fall into a harmonic imbalance on that interval. Does the harmonic change with vehicle speed? (bent propellor shaft, U-joints or rear gears) Does the harmonic change with engine speed? (Flywheel, clutch, pressure plate) How about with vehicle speed and related to specific road surface? (Tire balance, wheel bearings / axle bearings, propeller shaft, yoke, tailshaft bearing).

You may also be feeling the impact from one or more rubber bushings (rear trans mount / engine mounts) which are oscillating in harmony with something else listed above. Know anybody with a chassis dyno that would let you hook it up and get under it safely?

Does it do it in neutral? Then its probably engine related, otherwise I would check the ujoints, driveshaft,
tail shaft out of the tranny, working my way back to the tranny. I wouldn't rule out rear end issues but
I'd start with the easy ones.

How about fluid in the tranny? You could try thinner or thicker fluid and see if it changes. The other thing
that comes to mind is the pilot bearing or pressure plate. Of course that means dropping the tranny.