The stock center bearing retaining plate on a W56 should be fine. My W56b was a nice machined iron plate...........
I will wager to say that every single W56 and W59 that has come through our doors has had a worn our center bearing retainer plate. We mic and immediately discard any piece that fails inspection. It's this very reason which prompted us to manufacture our own plates (see
here and
here) but we haven't released a W-series plate yet but do have plans to eventually.
Part of the problem is with the main and counter shaft bearings and is why Toyota redesigned the bearings in the later model W59 Tacoma transmissions with a higher axial load rating. Needless to say the Maximum Capacity bearings we use in our Heavy Duty rebuilds far exceed the axial rating of even the upgraded W59 bearings. As the bearing wears it allows more lateral movement.
The other part and larger contributor to the problem is with the center plate wearing out. As the bearings push into the retainer plate for many, many miles, the plate begins to bow and looses contact with the outer race of both bearings (main & counter shafts). Once the plate bows and a gap forms between it and the bearing race, the issue gets worse exponentially with mileage to the point that the main shaft moves laterally in the case. Because the shift forks are mounted to and fixed in place with the case, what happens is the shaft moves without the shift fork and the
shaft itself positions the shift collar away from its mated gear thus "popping" it out of gear.
One of the most time consuming facets of our transmission rebuilds revolves around the center bearing retainer plate and the modifications we do to accommodate our stronger bearings. A great deal of focus is done here and is a major contributor to why our transmissions last so long. In my opinion if Cj's rebuilder simply slapped the worn out center plate back in place 47k miles ago without performing any supporting modifications to reduce or as we do eliminate free-play, then I believe this would be a very plausible cause to his shifting issues he is experiencing today.
Of course this isn't to say that even a pristine center bearing plate can't last 47k miles as we know stock original units can go 200k+ with only minor caveats. Maybe his plate had a lot of previous wear? Hopefully, however, it is something external like the interior boot bunching up between the shift handle and the body.
Regards,
BigMike
