My tranny broke!

["Robert H. Hughes" <robhughes100@domain.elided>]

Harvesters,

I drive a '75 with a 727 and 345.  Earlier this evening, I was pulling
away from a stoplight when I heard a loud, metallic, clanking, breaking
sound.  It felt like something in the drivetrain had broken.  I still
had a little bit of coupling -- by revving it pretty high I limped
through the intersection and into a parking lot.

I parked the truck and looked underneath.  Nothing visible was broken,
and no fluid was leaking.  I thought maybe the transfer case had popped
from 2Hi into Neutral.  But I got back in, and after reseating the
T-case lever into 2Hi, found that Reverse worked fine.  But none of my
forward gears would work.

That's where it stands now: reverse works fine, but I get nothing from
the forward gears, not even the really weak coupling I had right at
first.

I know nothing about automatic transmissions, but looking through my
service manual makes me suspect the rear clutch.  Does that sound
right?  How bad is that?  Anything else I should have the tranny shop
check?

Thanks,

Rob H.