First tried carrier bearing; people blame carrier bearing for vibration- in my case it had supposedly sagged. purchased the eurethane one. still had vibration. looked at condition of CV joint - galling
Purchased new driveshaft
still suffering some vibration- on partial throttle but not at full or off-throttle.
Identified that it seemed to only be in 5th and 6th gear, and the frequency was that of driveshaft speed
Tore down spare T56 transmission and found worn splines on 5/6 driven gear cluster and mainshaft
Appears that this is a common problem with T56 transmissions, at least for the CTSV
The spare I had was rebuilt before i got it by rockland standard gear, it had worn splines
the transmission i was removing from the car was also a rebuild, unsure of rebuilder. It clearly has the same problem (haven't disassembled yet
Rebuilt spare t56
Two different mainshafts depending on if uses c-clip or 3/4 piece retaining ring for 1rst gear slider
Quick notes for now, will update with pictures and such later
(it appears the way the 5/6 driven gear is held in place is that its sandwiched in place by the main case bearing beneath, and the reverse synchro collar on top, with the c clip that holds the reverse synchro in place retaining the gear as well. There is some slop here.
When moving to brass shift fork pads, you may not be able to remove the shift lever guide without removing the shift pattern plate (shifter guide plate) underneath- on disassembly i removed without, but upon reassembly there wasnt sufficient clearance to.