So, that makes sense. This is actually one of the mechanical tests. You'll see that in the 1995 service manual.
If the coast brake band lining is worn, you can just replace that. It's midway down the case, so you don't have to tear the entire assembly apart. You do have to pull the overdrive and direct clutch assemblies (and put them back in later, obviously) to get it out, and that's the worst part of the job, IMO.
Common wisdom is that if you're going to the trouble to open the transmission, you might as well do everything that can be done, because it's not a trivial exercise. Having said that, there's no reason not to fix only what is failing now. The downside is you'll have to be back in there at some time in the future; when that is depends on the current condition of (primarily) the friction linings and the use the truck sees.
There are
aftermarket kits, from all major transmission parts suppliers, Transtar, Transtec, Sonnax, Sun. Most use Raybestos clutch discs. They come in three flavors: overhaul (seals and O-rings ; pretty much a waste a money), banner (no steels), master (with steels). FWIW, I'd be very surprised if, after you invested the time and money to open the case, replace the parts and reinstall the transmission, that you'd get another 30 years of service if you used aftermarket parts.
Parts are still available from Toyota, although the rebuild kits, for some reason, are not.
Aftermarket kits, from what I've seen, run about $200. Toyota parts will be about twice that, not including shipping and tariffs.
I can provide you with a list of the parts which was in the overhaul and rebuild kits, if you want to use Toyota parts. Most of the online parts sellers can get them. My recommendation would be to contact Dave
Stedman at Japan4x4.com and buy what you need from him. At a minumum, I'd recommend replacing the seals and O-rings, as well as whatever friction lining parts need to be replaced, as indicated by the current operating failure.
Also, a final thought: common wisdom is to replace the torque converter with a rebuilt transmission. The thinking is that you can't test them, only a TC rebuild shop can do that, and you can't clean them, so anything left in them will make its way back into your new, spotless transmission. An aftermarket TC will set you back between $350 and $500. There are no new units available and the aftermarket units are rebuilt Toyota units.
