I have asked this question here before, but I'll try and ask again. I have a T-5 and when I am in 5th gear between 50 and 60 MPH I have a rhythmic vibration that shakes the car in slow oscilations. If I take my foot off of the gas, it stops, or appears to stop, but as soon as I put it on the gas again it starts back up. Can anyone help me out with some suggestions??

 

Bad U-joints, loose pinion nut, worn-out pinion bearings, worn slip yoke, worn extension housing bushing

 

Could also be a broken reverse lock out spring. 5th and reverse share the same shaft. If the spring is broken the reverse gear floats free and finds it way onto the shaft. Makes alot of noise but not doing any harm. Slamming gears lately or catch reverse by mistake?