[KTL]

I think the 915 operation and bad rap has been inflated by many poor repair approaches and abuse.

By poor repair approaches I mean "rebuilds" that ignore blunted dog teeth, replace only the synchro friction band and reuse of the slider sleeves/rings. I think the sleeve/ring part is arguably the most important to replace because it engages the dog teeth AND the synchro friction band. But yet this part seems to be the one most people look at and assume it looks OK visually and they put it back in.

Another bad repair approach is so many people hope to fix the shifting with external fixes and fluid change. Sure, shifter bushings and coupler bushings are important. So is a fresh gear oil. But often by the time those items need fixing, the internals of the trans have also suffered. Yet most are only willing to look at the external stuff and the fluid and hope that fixes things. Transmissions are really neglected by a lot of people. People will change engine oil all day long and debate what oil to death. But transmission oil is almost an afterthought to a lot of these same people.

Regarding abuse, I think some people believe the 915 is a tainted trans and there's just no chance of it ever shifting good. Reality is a lot of shifting is done really poorly and the trans can only compensate for that so much. A lot of people are notorious for yanking the shifter before the clutch is fully disengaged and the 915 doesn't like that. Over time that bad shifting habit can distort the dog ring by trying to pull its press fit off the gear.

Another abusive behavior that a lot of people are completely unaware of is matching RPM on downshifts. Not only does it wear out your clutch when you don't match RPM, but you also put more wear on the synchros. Sure the more modern cone style synchro G50 transmissions are better at managing unmatched RPM, but even they will eventually start crunching. I had an 83K mi. G50 in my '87 that was clunky going into 2nd gear when cold and would crunch 3rd gear during fast shifts when hot. So it had obviously seen a lot of heavy shifting to be crunchy at *only* 83K mi.

The reverse crunch is definitely related to the non-synchronized reverse gear assembly. It's not a problem with the trans in terms of it being something amiss. It's due to the lack of synchronization to slow down the straight gears as they're trying to mesh.

With the engine running, clutch out and trans in neutral, the shafts inside the trans are all spinning. Push in the clutch and those shafts begin to stop spinning. If you quickly go for reverse while they're still spinning somewhat quickly, you'll get the crunch every time since the reverse slider hub has nothing but bare, albeit rounded-edge, straight teeth on it that are attempting to engage with the same type of teeth on the reversing gear pair. But if you select another gear like 2nd or 4th or whatever other gear before you go for reverse? You're using that other gear's synchros to slow down the spinning shafts and that's what lets you get into reverse without crunching.