On The President’s Tour in June I noticed oil was dripping rapidly from the U-joint / ball cap. We completed the tour, about 50 miles, and since then I have taken the T on several outings. The oil is still dripping but maybe not as fast. Even after all the driving oil still runs out of the top petcock, so I must have overfilled the engine at the last oil change. This may have encouraged the drip.
Yesterday I took the Model T to Bowness Auto to pick up a rad hose for our T-bird and noticed a dull thud or thumping sound when the engine was under load. I emailed Harry about the problem and we independently came to the conclusion that the grease had been washed out of U-joint / ball cap by the oil drip.
I pumped grease into the ball cap until my arm got tired and took the T for a short drive. Problem solved, or at least the symptom is masked.
Here is what I learned:
The oil level only needs to be above the bottom petcock. My accidental overfill promoted the leak
A dull thumping sound under load may be emanating from the universal joint.
In addition to lubricating the U-Joint and reducing oil seepage down the driveshaft to the differential, packing the ball cap with grease reduces the thumping noise (which may be caused by a worn U-joint or perhaps the joint is loose on the driveshaft*).
* I am using a modern pinion bearing and did not pin the U-joint to the drive shaft)
Update August 6,2014: We drove the T over 1,000 km last week without incident.
Update September 14, 2014: the loose U-joint was replaced with an NOS joint and after a 100 km test drive the thumping sound has not recurred.