Over the past couple months I have noted that my girlfriends transmission was quite noisy. She has a 242 with manual transmission with overdrive. So I checked the fluid level and found it really low probably at least a quart and a half low. I replaced the spedometer drive seals since I had them on hand and refilled transmission with new atf type f. While I was under there I also replaced soft and soggy transmission mount since I had a new one.

Well the tranny was less noisy and the overdrive engaged much more positively. But now there is a significant rumble in the whole car at speeds of about 55 to 60 mph. The rumble is low, very pronounced and rattles the plastic of the car. The shaking is present at these speeds even with the car out of gear.

Could the tranny be shot due to prolonged dry running? Is this a driveshaft problem that has became more pronounced when I replaced the soggy tranny mount? What else could it be? How can I positively diagnose a bad u-joint? Could I have remounted the tranny support crooked enough to cause this? Could it be the drive shaft support bearing??

Any help would be greatly appreciated.