Several things come to mind to check...
mismatched front to rear u-joint working angles
excessive u-joint working angles (this is the cause of my high speed vibration, I need to raise my entire tranny tunnel for more driveshaft clearance so I can raise both the tranny angle and rear end angle to minimize the total u-joint working angles.)
runout issues on either slip yoke or pinion yoke
worn & loose output shaft bushing in transmission
driveshaft runout / balance problem
If it's speed related and not RPM related as you said (the vibe occurs at a given speed no matter what the gear) that pretty rules out the clutch & flywheel as the problem and points to the driveshaft on back as the source of the problem.
It could also be a wheel, axle, or bearing problem too.
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1969 Chevelle
Old setup: Procharged/intercooled/EFI 353 SBC, TKO, ATS/SPC/Global West suspension, C6 brakes & hydroboost.
In progress: LS2, 3.0 Whipple, T56 Magnum, torque arm & watts link, Wilwood Aero6/4 brakes, Mk60 ABS, Vaporworx, floater 9" rear, etc.
Last edited by Blown353; 12-10-2007 at 01:06 PM.
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