Gents:
Just my $.02 worth.
A couple of years ago when I started on Iron Annie, my 52 3/4 ton pickup, I wanted to swap out the ring and pinion for a more interstate friendly rear axle [numerically lower]. Found out as is mentioned in ths thread that the pumpkin from to a 72 3/4 ton is the same. Contacted many sources, before finally finding out from the folks at Randy's that the highest [lowest numerically] ring and pinion ratio available for that rear is/was a 3.90:1. Randy's actually had made a special production run on them, because of demand. I believe they are now sold out. The existance of a 3.55:1 3/4 ton Eaton rear is a possibility as GM typically offered higher ratio rear axles in automatic equipped trucks. I've just never seen one in a 3/4 ton. I have heard that the 3.90:1 is the highest [again, lower numerically] ratio R&P that will fit the Eaton rear because the higher ratio R&P's are dimensionally larger and won't fit it the housing..Can anyone with hands-on experience with these R&P's verify that this is infact the case..I do know that when we put the 3.90 in the pumpkin on my truck that the clearances were tight,really tight. It would be interesting to dimensionally compare the 3.90:1 to a 3.55/56:1 to see what the size difference is.
I may just phone Randy's to see if they've got that information.
