Transmission Vibration

[ss_0195]

I recently brought a series 2 vt with a LS1 and it has a vibration coming from the transmission I think . i had a 98 mdl 5ltr witch i smashed so i swapped out the tailshaft thinking it could be a uni or a center bearing and it still has this vibration. it only does this after driving for 10 minutes or so and only when cruising and backing off ,it disappears under acceleration. the transmission shifts fine. according to the tag under the bonnet it is a M30.
Any help would be appreciated

One other question as well, both the 98 and 2000 vt tags say that the transmission is a M30 even though one is a Ls1 and one is a 5.0ltr are they the same or is the bolt pattern on the bellhousing different ,if so are the bellhousings interchangeable like older transmissions e.g trimatic.

[pablo]

Have you checked the engine mounts?

[Cúl-Báire]

As above, I'd be inclined to think it's either the engine mounts are saging / cracked, or the transmission mounts are sagging / cracked.
Worth a look before swapping out the gear box.

[ss_0195]

No i hav'nt but was thinking that the other day and I dont know of a way to check them without installing new ones i did check to see if the engine lifts on one side when reving the engine and didnt notice anything out of the ordinary. i also thought it might be the gearbox mount also .its strange that it dosnt make this vibration until it has warmed up .
thanks for the quick responce pablo if you know a way to test the engine mounts please let me know

[D3CID3R]

Check the shift plate/mounting plate for cracks