I have actually dug into both my gearbox and rear end, but both times had to run up to my BMW mechanic buddy's place with tail between my legs.
I just could not make the special tools required in my workshop with no lathe, drill press or welder. Plus I did not have a dial gauge to send end plays. I usually set end plays in Harley gearboxes by feel and it works fine, but BMWs are so finicky in that department I would not dare.
And Triumphs, well what end play?
I finally got a good heat gun and propane torch so I can at least dismantle my own rear end, but took it to the maestro who had the shims and dial gauge to set the plays.
And after watching how he does it - an aircraft engineer with 30 years of working on Airheads on the side - there are a lot of small but esentially important tricks you must know, and the manuals do not tell you.
He makes a good living on the side repairing gearboxes and rear ends that have been rebuilt by amateurs and some professionals who work on other bikes and think they can do the same with Airheads.
Despite that, here are some pics of my homemade tool to remove the input bearing collar on my airhead rear end.
I made it out of a threaded water pipe connector, 1.5inch nominal size, I think.
Put some bearing blue on the threaded input bearing collar so it made a mark on the pipe fitting. I then scribed those lines and cut away the metal between the four tags. Using more bearing blue for a final fit.
Then I cut two slots in the other end to fit my large square shank screwdriver, to turn the tool with.
Bolted the rear end to the bench. Heated it spitt sizzlin hot with my heat gun and propane torch, and unscrewed that input bearing collar. Bit of pipe over the end of the screwdriver provided torque to overcome the Loctite. But it actually popped out reall easy. Two hours to make the tool. Two minutes to do the job.
Crude yes, but the working parts were a nice fit for a nice drive.
And here is how I locked the rear end to get the input drive nut off before all this:
Placed the bevel unit on the wheel, splines engaged, and used a ratchet tie down strap wrapped around the input boss and the tire and spokes to stop the bevel unit from turning as I torqed the input nut til it came loose. Applied torch also to overcome Loctite.