Bad Vibration between speeds of 75-85

When driving my car handles fine till I reach 75-85 mph, and then it feels like the whole drive line is shaking, it is more in the middle of the car, not like an alignment, steeering wheel vibration. If I go past 85 the vibration gets better and seems to go away, when slowing down and entering those speeds again it does it again, has anyone experienced this, or have any ideas?

yeah...not sure of speer, but at 2500 to 3000 rpms...quite until 3200 and start again. mostly 3rd, 4th and 5th. had driveshaft re-balanced. still there. after about 1500 spent on trans and rear...replaced with aluminum driveshaft...all is good now. shop claimed hole for u-joint cup was too big...bullsh..I think the driveshaft was buckled somewhere and they balanced it like that. bad u-joints can give the same effect, especially if they are siezing up

I started having the same problem after I installed my new Spec Stage 3 Clutch/Pressure plate, and Tremec TKO 600 tranny. The tech at Tremec told me that my driveline could be out of angle. So I shimmed the tranny 3/4" and it still does it. I also have an aluminum driveshaft that was fine before the tranny swap. [img]/forums/images/smiles/icon_confused.gif[/img]

i would check u-joints and the rear flange where the drive shaft bolts to the rear end. i had the same problem. when i got to a certian speed it would shake like crazy. the bolts seem to back them selves out quite often.

countryboysmustang is correct, i had that same problem and that is what was wrong, spend the money once and put in a new aluminum drive shaft and kiss the problems goodbye!