Originally Posted by recycled_toddler

I just opened up an RS5F31A an hour ago; Internally, it seems impossible to bend the bellcranks and the rod between them and the outside linkage. Also, the shift forks are cast aluminum, suggesting they'd break before they bent. I can't picture what it might be, but you might wanna just drop another tranny in 'er. Save the old one, I wanna do an autopsy. Part o' th' learning process, y'know...

I found why mine wouldn't stay in 5th: 5th gear dogs mostly worn, baulk ring wearing out, synchro sleeve dog tips worn. It appears I can flop the synchro over and use it again, but the gear and baulk ring are definitely toast.