Grease cup or a zerk fitting to lube the u-joint
picture of grease cup
This plug. One on each side.
Bruce has it right, the U-Joint housing plug and there should be one on the top of the drive shaft tube, also.
a large grease cup for the u-joint. If you want to grease it faster use a zerk fitting.
Those two holes (one top, one bottom) are used to install or remove the pin (like a long rivet with small heads) that holds the U-joint in place onto the drive-shaft. This pin is extremely important on any standard model T drive shaft with original type pinion bearings as the back flange of the U-joint establishes one direction of thrust and maintains position of the pinion gear. Without that pin and U-joint properly fitting, the drive-shaft and pinion gear would at times slip back a bit and begin grinding up the ring gear and differential parts.
Once the driveshaft position inside the torque-tube is established (both forward and rearward thrust adjusted), and the pin to hold the U-joint is properly placed (and peened), then both the bottom and top sides of those holes need their plug/bolts put in. The link provided by Bruce S looks right.
The other side of that torque tube should have an additional hole for a grease cup.
Lots Grease First....
Actually that's the opening to drive the pin out of the U joint. You should have the a grease cup or zerk fitting on top of the of the ball retainer. Mark sure the opposite side hole also has a plug like Bruce shows.
By the way, your lock washers should be on the back side of the flange, in front of the plain nuts, not under the castle nuts.
The castle nuts are already locked by the cotter pins.
Mark, you make a valid point about the lock washer position. However, that little bit of extra length of the radius rod can make a difference when fitting the rods to an assembled diff. Backing the nut right up to the end of the thread will usually allow the rods to be fitted up after the torque tube/tailshaft is fitted. The washer may not allow this. Been there, done that.
Allan from down under.
Plug top and bottom for the u joint driveshaht coupling
Allan, I guess you do what you have to do when the parts won't fit like they should.
When all the parts were new, the lock washers were on the plain nut side, see the Ford service manual, page 153, paragraph 621, step (a).