In response to the "ring gear is deflecting" train of thought, of course it deflects some. but I believe it's more pinion deflection. Basically the major thing the Ford 9" has over the 8 3/4 or 9 1/4 or 12-bolt is the pinion support. That's what seems to me to be making the difference between 8 3/4 and 9".
My friend with the '63 Corvette broke countless 12 bolts before switching to a Dana 60 and hasn't broken anything since.
R. I don't know, but..... If ring gear deflection isn't an issue then why do main bearing caps fail? Pinion flexes, teeth break and stack up b/t the pinion and ring gear...carrier gets bound up and pushed backwards, cracks the cap.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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