So my 5sp 1987 RX7 started having this vibrating problem and i don't know where to start.. it started off as a rattle that only happend when the car was in gear and i accelerated. it also sped up with the speed of the tires spinning, however it would only do it in gear. now the problem is worse and anywhere above 25 mph, or anything after second gear especially would cause vibration..

now it even does it in neutral when up to speed. it vibrated so bad my cds cant even play and i dont want to ruin my beautiful car. also i noticed its rear end.. or something has a little play when gassing and letting off. like something in the drive train is loose. perhaps the drive shaft is loose? maybe a yoke or a u-joint? i have no idea, please give me feedback if you might know anything!!! thank you for reading!

 

A worn out u-joint or two would be my guess. You can jack the car up, and see if there is any side-to-side play in either end of the driveshaft.

http://www.mazdatrix.com/g2.htm