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.

Does this rumble happen both in and out of gear?

I second the U-joint. Replaced mine a few thousand ago and now its smooth again.
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Simon 80 240 290k 17 years.

Possible suspects: u-joints (which may also 'clunk' when going from neutral to D or R); driveshaft center bearing; worn engine and trans cross-member mounts. Also, if the driveshaft has been removed to service the tranny (or anything else), it's possible that the 2 driveshaft pieces were re-installed out of alignment. The 2 halves are stamped with arrows to aid in alignment when re-installing, and they could be mis-indexed.

I would go for a bad u-joint some where. The softer/worn trans mount you replaced could have been taking some of the vibration away from the bad u-joints. I would also take a peak at the engine mounts to see if they are in need of some R/R. Good Luck!

Sincerely,
--
Julio Meza

1979 264GL B27F 122K

Features Added:

BW55 To M46, Central Locking System, 25mm IPD Front Sway Bar, 81+ Dash W/ Oil & Ambient Temp Gauges In C, Oil Pressure, Volts

Next Project:

+Cruise Control

Try replacing the bushings (probably in the rear). Those things can make a ton of noise and vibration at highway speeds.
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If you listen to the radio in Portland, OR, you may know me as "Portland's Favorite Soul Brother!"