A few months ago, I installed Kooks headers, Yank SS3200 T.Q., and
FLT (Level 3) auto tranny to a standard rubber tranny mount. Just prior
to that, the only other things I've done is add a Meziere electric pump,
ignition wires, plugs, MSD cap/rotor, new Yokohama tires all around.

A couple of months ago, I replaced the broken stock rubber tranny mount
with a poly mount and noticed an increase in vibration. But in the last
month, or say, 1,000 miles, I've noticed a fairly "violent" vibration. I've
rotated the driveshaft 180 degrees with no improvement.

The vibration occurs mostly between 1,800-2,000 RPM, and seems to be
most apparent in 3rd gear - if i manually shift through the gears, it's not
so noticeable in 1st or 2nd, but is most noticeable when i shift into D. In
fourth, (circle D), it's not as apparent.

I have also noticed one other thing. Let's say I'm running at 50+ MPH and
above 1500 RPM and I let off the gas. When the RPM's hit 1500, the tranny
downshifts to 3rd VERY noticeably (never did this before). Also, if I mash
on the gas (say, from a stop) conservatively, the tranny shifts into overdrive
prematurely, at around 1500 RPM at 45 MPH, which it never did before.

So here's my question - and I'm mostly interested in determining the
vibration problem now. What is the best method to determine where the
vibration is coming from? Could it be the flywheel, harmonic balancer,
torque converter, tranny, or driveshaft components?

How can I reliably eliminate where the problem could be coming from?

 

Anyone?

 

You may want to post this question in the Drivetrain section for better responses.

 

i have a similar problem but havent been able to diagnose yet

 

I read a post about the poly mounts and they said the vibration was pretty rough so if nothing else going back to stock on that might help some.

 

I chased a vibratin for a long time and finally found that my exhaust was ever so slightly rubbing against my rear end housing. Check your exhaust and make sure that it has clearance