Like TB said
In order to swap tail shafts you have to remove everything in the transmission.
EVERYTHING
But, you may be able to swap the entire truck geartrain into the burned up trans, or just the clutches and bands; and be back on the road in a few hours. IF
I say IF, the gaskets survive the transplant ............ which is not likely. SO
Since you gotta buy some parts anyway, you
Might as well put new stuff back in.
IMO, 904s are the easiest transmissions to learn on, I did my first one in 1976, at the age of 23, and yes, the build was successful.
You can do it!
But you will need a couple of specialty tools. namely;
a rebuild-manual,
a small torque-wrench,
a Circlip-plier,
a clutch compressor,
a feeler-gauge,
and something to pull the pump out with. Some guys use a slide hammer, some use a chain, but I use my heel-bars and a couple of bellhousing bolts. It can be done with just one heel bar, but two is vastly better.
The trickiest part of assembly is getting the pistons back into the drums. I use the slipperiest lube known to man, Silicone O-ring Lube, from the company that builds the Fuller Roadranger Transmissions. You're gonna find a million uses for that lube, after you see it work.
Hint, before you take it apart, measure the geartrain endplay. This well help select the endplay washer, when it comes time to put it back together. If you forget to do this now, you will have to assemble the trans hoping for the best, but expecting to pull the geartrain back out, to select-fit a different thickness washer. which is just extra work
