it's my understanding that a 8" chunk will fit into a 9" housing. that's what some old ford fellows have told me. an 8" diff is so much higher in price then a 9" diff. so this is my question. can you cut the back off both the 9" and the 8" housing and swap them? put the 9 on the 8" and make a 9" housing? is the only difference the bump on the back of rearend? same bolt pattern? my daughter's mustang has a 8" rearend but to get a posi 4.11 is big bucks. i have 3 or 4 9" gears here for a 9" rearend. is there a cheaper way? kendra's daddy!
probably should be in the tech section. probably cheepest to get a 8" posi. I've seen an morph of a 9 & 8 once. But not like your thinking. The guy cut the 8 inch tubes off and welded them to the nine inch, so he used the tubes and brakes from the 8 inch.
Y'know, maybe it's because I live out here in the middle of the friggin' desert and most people don't know what to agressively hunt down; but there are still a few V8 Mavericks, totaled late Torinos, Moose-stangs and Cougars with "back feet" around these parts. I think I'd go junkyard-divin' for the real deal before I tried to build an 8"/9" Frankenaxle - especially for a car my daughter is driving. Extra-especially not for Cowgirl Tink; I heard she tried to create a 3-wheeled Humvee while playing around in one of the swamps at Ft Polk But that's just me.... YMMV
Regular 28 spline axles work in both an 8 and a 9 inch Ford rear as to the brake assemblies, so there's really no need to swap tubes at all.
the reason for the tube swap is to have the correct length. actualy you'd be swapping the center section of the housing from a 9" in place of the center section of the 8" housing. lot's of people do this on 65-66 mustangs because of the necked down axle tubes. if it's a 67-up mustang then it's much easier to replace the rearend assembly since the axle tubes don't neck down like the 65-66 ones do. to specifically answer the question that was asked though, NO, you can't do what you are thinking about doing, the 8" is a lot smaller than the 9" and the 8" housing is physically too small for the 9" pumpkin, also the bolt patterns for the carrier are different as well. you can do as stated above if it's a 65-66 car or just swap the entire assembly if it's a 67-up car.
