7.5 and 8.8 Ring &Pinion the same??????
 

I was wonder if the 7.5 and the 8.8 use the same ring & pinion?same part #? same strength?etc...?

no im pretty sure they are different. I believe that the number is the measured diameter of the ring gear in inches. So the 7.5 is smaller, thus weaker then the 8.8 (i think that is what it is)

so the size of the gear is what makes the axle a 7.5 or 8.8

Yes.

There are a couple people i know install'n these 7.5 gears(3.55 out of a Ranger, brand new warranty replacement) for cheap. I guess they are no good since they're weaker?

Yes, they're weaker. It doesn't make sense to go in the wrong direction just to save some money.

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351W 89 Mustang GT Convertible

They are weaker but in a stock car if you just want to free up some power I say go for it. My 84 had a 7.5 uo until last year. The diameter of the ring gear does make it weaker b/c it has less meat and 7.5 rears run warmer b/c the are smaller and the area of the ring gear has less time to cool but they are decent and I actually liked the posi in my 7.5 alot better than the 1 that's in the new 8.8.

later,
Violent

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84 GT-350, 2.5" Ram air hood, Centerline Pintails, 5-lug conversion, Recaro's, 140 speedo, 8.8 conversion, 3.73's, Motorsport A/C eliminator, Hurst shifter, ASP pulleys, Eibach pro kit, KYB's, Flowmaster exhaust, Long tubes, Flowtech off road h-pipe, .030 overbore, Extreme Energy 268, AFR 185's, CC Hi Tech Pushrods, CC Pro Magnum RR's, Pete Jackson Gear drive, 750 Speed Demon,Aeromotive 1000 hp pump, Aeromotive FPR, Aeromotive fuel filters,Weiand Xcelerator intake, Max Motorsports aluminum rack