Just finished narrowing a 31 spline 8.8 from an Explorer. Have new axles and the proper install kit with all the bearings, crush sleeve, shims etc. Even have a shiny new aluminum finned rear cover. Lets say I was to change the gears on this thing. I see lots of choices on eBay. Do those gears fit all 8.8s or are there different sized pinion shafts based on the whole car 28 spline vs truck 31 spine? I know the wheel bearings at the ends of the tubes are bigger because the shafts are bigger. What I don't know is are the bearings on the pinion and the pinion diameter different between 28 and 31 spline. I can't find any that are listed as Mustang or any that are listed Explorer/F150, so I assume the R&Ps are identical, and just the housing tubes and carriers are different. For now the 3.73s will do, but I suspect a gear change is in order. Whats the preferred gearing on a Miata with an LS engine and a 6 speed with a .50 6th gear? Tire size and weight will be close enough to what I'm building.
I don't have answers to your technical questions, but I assume this means the LS swapped TR8 is staying stick axle instead of the IRS you were considering. I've been following your build thread on that other site, and I'm really excited at the prospect of this getting closer to completion. 
Figuring on 23" tall tires, with the 3.73s and 0.50 6th gear, you'll turn 1900 RPM at 70 mph. 6000 RPM in 1st gear (assuming it's a 2.66 in that trans) would get you 41 mph.
So that gearing might be a little tall on the low end, but it's certainly in the ballpark IMO. You could go to 4.10s (37.5 mph at 6k in 1st, 2100 rpm at 70 in 6th). In a light car, you probably don't need more than that.
All 8.8 housings/carriers are compatible with any 8.8 gear ratio, except for reverse rotation r&p's.
Todd when you refer to 28 or 31 Spline axel.... do the 8.8 rears have that option, I thought that reference was for 9" rears ?.
The number of splines is determined by the diff. and more specifically the spider gears.
OK My Brain was in Factory Mode. I know you Can Buy Anything.
Thanks guys. This is going in the LS3 TR8 for now. Just couldn't make the Camaro uprights work without going to 18" wheels. Those hunks of misguided aluminum are huge. Still contemplating doing a swap using a Tbird IRS setup like the Cobra kit guys car do. There is a TR7 in Western Canada running a 5.3 with a 6 speed and he went with 4.10s. Still can't wrap my head around how low the rpms must be in the Camaro with those huge tires and a 3.45 rear gear. The car based 8.8s use 28 spline axles that are the same as the 7.5 rear ends. The truck based 8.8s use slightly thicker stronger 31 spline axles. Thats why the Explorer axles are so popular. Narrowing the long side 2 7/8" to match the short side, and buy one more shorter axle yields you a bulletproof rear end that has wheel mounting surface to surface mounts of around 57". Perfect for stuffing under all kinds of sporty small cars.
thanks, Now I Know, My Friend Lance Swears By them, and that's better than Swearing at Them.
obviously pay attention to the carrier. There are a couple different diff thicknesses; one holds gears up to something like 3.23, then another holds 3.23 and up (numerically).
As you go up in numeric ratio, the size of the pinion gear decreases. In order to keep the ring gear placed properly, the carriers for higher numeric gears have a different "offset" where the ring gear mounts. Just be sure you swap gears that fit the carrier's offset.
Worthless tidbit of trivia. The Ford 8.8 is a corporate ripoff of GM's 12-bolt. They are just different enough to avoid legal issues, but they are really close copies.
curtis73 wrote:
obviously pay attention to the carrier. There are a couple different diff thicknesses; one holds gears up to something like 3.23, then another holds 3.23 and up (numerically).
As you go up in numeric ratio, the size of the pinion gear decreases. In order to keep the ring gear placed properly, the carriers for higher numeric gears have a different "offset" where the ring gear mounts. Just be sure you swap gears that fit the carrier's offset.
Worthless tidbit of trivia. The Ford 8.8 is a corporate ripoff of GM's 12-bolt. They are just different enough to avoid legal issues, but they are really close copies.
There is no ratio splits with the 8.8 carriers. Same carrier can have either 2.73 or 5.71 gears installed on it.
@weedburner: You beat me to it.
