Urgent 9" rearend knowledge needed

[motzingg]

these are some great things to think about. good to have the right terms, i should probably have started all this by reading the damn wikipedia article so i knew at least what i was talking about. i've always heard all 4 (8) of the gears inside the differential 'spider gears'... pinion gears seems confusing as the input shaft pinion gear is more commonly referred to as the 'pinion'... but yeah i get ya.

Without tearing into the thing i don't really know whats good and what isn't. I should probably just buy the rebuild kit for the 28-spline diff, and put the 3.0 gears from the 31 spline diff in it and sell the leftovers.

would the bearings and everything (and now i'm gonna really sound cheap) out of the 31-spline carrier all go into the 28-spline carrier? I guess i cant get them off.

Ehhh, all this is just made a lot tougher by the fact that to put in the transmission i need to make a driveshaft, which i don't want to do unless i have the diff sorted out. I cant take the diff apart unless i have everything ready to put back together, and i cant have it ready to put back together until i know what i need, save up the cash, and buy the right parts!

ah!


and yah, you guys are probably right about the 28 spline axle thing. I am eventually hoping to build a high torque turbocharged 300 for this truck, and i want everything to be solid from the flywheel back for towing heavy stuff across country.

the only reason i get hung up on the 31 spline thing is just because Fomoco decided it was a good idea. They weren't building anything in the 70's that made anywhere near the 300-400 ft-lbs i'm hoping for, yet they felt like they had to make the switch for some reason? were there failures? Aside from the extreme off-road community or drag racing i've never heard of anyone breaking axles as like, a common warranty claim thing. I guess my transmission is only rated for 300 some foot lbs, which when you factor in the relatively tall rear gear doesn't provide much opportunity for overstressing the rear axles.

the bottom line is when i have the chance to fix something and fix it forever, i want to do as much as my budget and skills will allow, i just don't have any knowledge base for this kind of equipment, experience wise.

[motzingg]

and once again thanks so much ultraranger and everyone else who has helped with this process.

[ultraranger]

Glad if any of my information helps you out. Building/setting up a 3rd member requires some knowledge and at minimum a dial indicator, to measure case spread, and to measure ring and driving pinion backlash. You'll also need a beam-type in/lb torque wrench to measure driving pinion preload and a ft/lb torque wrench to tighten the ring gear bolts, carrier bearing caps, pinion housing bolts and the large nut on the stem of the driving pinion. You'll need a spanner wrench to adjust the spanner nuts on the differential bearings to set the ring gear/input driving pinion tooth contact pattern. You'll also have to be able to read the clutch pack height for proper differential engagement. A mistake(s) in setting up the gears can lead to a 3rd member that won't last long.

There's a very good how-to-video, by Bad Shoe Productions, showing how to rebuild a Ford 9-inch 3rd member. It's available on DVD or (now) through digital download. http://www.badshoeproductions.com/rearends.html. It's a good video that's well worth the price.