8.75 Sure Grip spider gears break

what are you doing when they shear?
did they break once you get back on the power after threshold braking prior to turn-in?
if so, do you down shift prior to turn-in and braking? Are you religiously rev-matching when down shifting?
I have seen guys bust the rears in Cortinas and MGs because they fully lift when down shifting/threshold braking, don't rev-match, then go wide open through the apex. Even with a low tq motor, shock loading the drive line like that over and over is going to highlight any weaknesses..

I race a '68 Zink C4, so breaking a rear end isn't exactly a concern for me with the massive 49hp she builds :)