I'm in the process of putting together a new B30 long block
with a spiffy isky cam and good used pistons new bearings and
so on.

Anyhow -- I've got 2 M410 transmissions that I've pulled out
of a couple of salvage yard cars. Both cars were junked for
unknown reasons.

Is there any way to see how noisy the transmission is going
to be prior to putting it into a car?
chris

Maybe you could turn the input shaft with a big electric drill and
put some load on the rear flange...
Use second and third gears.

You could certainly inspect the gears by pulling the top off
but the noise is generally from the bearings you can't see.

Usually the gears look like they haven't been used.

If there is water or rust inside, you can pretty much count on bad
bearings
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

Second on the notion that visual inspections aren't much good. I took a good look inside the junkyard M41 I got for my PV as I swapped the remote lid for the long stick lid. The gears all looked nearly perfect (a few chips on reverse). Everything looked entirely good. Then, once installed in the car I found that #1 and #3 syncros were totally MIA. On the bright side, however, there's no noise in any gear and #2 and #4 work perfectly. As does the OD.

I should also have added that the M400 that's in it right now is
silent in all gears (except for the shot syncros in 1st that make
downshifting into 1st kinda crunchy). Also, the parking brakes are
kinda shot. That and I've got 195/60R15 tires which are kinda low
profile relative to what I could put on. So -- am I better off
playing transmission roulette or should I harvest a rear end from
an automatic 164 and stick with the known decent M400.
chris