My daughter's 1991 convertable non-turbo has a significant vibration in 3rd gear. If you engage the cluch (obviously a 5 speed manual) the vibration gets worse. If the clutch is re-engaged and released, the vibration decreases significantly. Also vibrates in 4th, but not as bad. If the engine is shut off during the vibration, it continues to make the same noise. Any suggestions? My manual says it may be the 3rd gear mesh. Any chance it's the drive shaft or U-Joint? I appreciate any help.

 

Vibration or noise? or both?

 

the driveshaft wouldn't do it if the car wasn't moving.

is the noise a grinding noise? if it grinds primarily when releasing the pedal, it could be a bearing. other than that, i would stick with the original diagnosis and say a synchro.

 

It can't be a synchro. More likely the pilot bearing is toast and destroyed the input shaft which would throw it out of balance. With the clutch pushed in the input shaft should stop. If the pilot bearing is that bad though the front input shaft bearing is probably damaged too.

 

Thanks for all the help. Turns out it was the driveshaft. I got a new one from mazdatrix and it runs like new. Now I need to pass emissions.