T-56 vibration

I have a t56(out of a 94 z 28) behind my chevy 350 and in nuetral iam getting a vibration from about 3700rpm on up.The engine has been balanced the clutch set up has been balanced. So what could be going on in the trans that would give me vibration? I have heard that pulling a t56 apart is a little tricky cause the case can twist. Is that so??? I pulled the trans and put a new pilot bushing (bearing type) some people said that might help but it didn't. I do notice that in 5th and 6th I feel some vibration also.
Angelo

What flywheel did you use? I have two T56 transmissions; one will go behind a Lt1 with stock clutch & flywheel and the second one is setup in my '40' Ford behind an early 350 sbc with a pricey flywheel from Centerforce #700107. If you have the incorrect flywheel the balance will be messed up. Hope this helps. I find it hard to believe that it is something internal to the trans if it was a good trans in the 94 Camaro before.

94z are internaly balanced--if you have a balanced clutch setup the engine will shake pretty bad

Hi Jerry,
As I recall the LT-1 is a 153 tooth flywheel with an external weight. I'm quite certain the external balance started in 1986 when the engines went to a one piece rear main seal.
What flywheel you use?

Somewhere along the line, someone forgot to tell you that the one piece seal 350 are external on the rear------or maybe you were just out of the room

I've rebalanced probably 12-15 flywheels for theLT guys---the Camaro/Firebird guys are switching between at and 6m and theres always a overlooked flywheel balance---those engines internal front/ex rear---gm didn't have to cut a keyway for dampner as spark being controlled by ecm---mech don t need timing marks---so GM engineers being the departmentalized group they are--the crankshaft guys internal the front but leave the rear external since one piece seal came out---

REmember when 396 came out???The intake manifold guys out ranked heads guys so head guys had to build intake ports to fit manifold-----

I recently changed the trans and vibration is gone. Not sure what was wrong with the other one, but all I care about is problem solved.

What do you mean by a "side bind "????
Thanks
Angelo