He damaged the sprag while in first gear causing the transmission geartrain to over-rev exploding the stock high gear drum.
It's very simple, install a billet aluminum or steel direct drum, and a valve body that applies the low/reverse band in first, and you won't have an issue.
Also, don't act like an idiot while in first gear with a 904/727 or any other automatic transmission that uses an over-running clutch. IF YOU GET OUT OF THE GAS WHILE IN FIRST GEAR, AND GET BACK IN THE GAS YOU WILL MORE THAN LIKELY ROLL THE SPRAG AND EXPLODE YOUR STOCK 727 DIRECT DRUM.
If you still feel that you may damage the sprag, keep your transmission out of first gear until you pull it into the stage beams.
I've been building these for ten years with low band apply valve bodies and billet drums. NO EXPLOSIONS TO THIS DAY...
