Classic/Antique Car Repair: Triumph TR6 transmission top cover, overdrive transmission, forward gears

Question
I have a J-overdrive transmission. I have modified a top cover from a 4-speed transmission that was originally on the car. To modify this top cover, I withdrew the 3rd/4th selector shaft and drilled and tapped the correct boss location for the O/D inhibitor switch. There are 2 stainless stl ball bearings located and a small plunger located (in the direction of the shift mechanism) between the 3 selector shafts. What is the purpose of these 2 ball bearings and plunger? When I tried to reinstall them (using grease as a temporary retainer, they fall out as soon as the shafts are moved. I might add they are not associated with the ball bearings, springs and reverse plunger that are located under the cap plugs that match up with the detents for neutral, reverse, and the 4 forward gears. These are separate and are all in place as necessary. The holes in the aluminum top cover casting that the shafts pass through are round and not excessively worn, yet there seems to be too much clearance (lateral) for the ball bearings and plunger to remain in the intended detents. Any ideas?  

Answer
Hi Mat,
The plunger and ball bearings that run between the three shifter shafts and match up to detents in the shafts are there to prevent two shafts from moving at the same time. When they are in place you will see that you can only move one shaft at a time but if you leave them out you can move two shafts at the same time which locks up the gears and you know what would happen if you were in motion.

As for the O/D inhibitor switch, they didn't want a driver to use the overdrive in first or second gear and they did not want the overdrive to operate in reverse. In first gear you may have a problem getting full pump pressure since the pump is driven off of the output shaft and if reverse is engaged the sprag bearing (one way bearing) in the overdrive will lock up and either stall the car or explode the case of the overdrive. I have had customers who had 1st and 2nd gear operation of the O/D and they took a lot fun demonstrating to friends that they had a 8 speed trans. However, reverse MUST be locked out as the sprag in the O/D will totally destroy the O/D if driven in reverse.
I hope this helps,
Howard