I want to upgrade my rear end to 3.73. I'm new at this forum and this is my first Mustang. I need help on part #s and where to buy cheap. They came with 8.8" Rear Gears from the factory, right? I found a Ford Racing kit at eBay listed for $248.33 w/ free shipping, ford racing part #M-4209-88331 and #M-4210-B2. Is this the one for my car?
You'll want to buy all of the other crap at the bottom along with it (install kit, pinion bearing, and traction LOK rebuild kit). Totalling about $400 in parts to do it right. Then, install should cost about $300, more or less. It's a half a day job for a shop.
If it's a 2005-2010, look for the proper gears on the American Muscle site. It is a pretty good parts store, they can usually point you in to the right direction. Like walking into a candy store for Mustang owners.
You don't necessarily need to rebuild the trak lok while you're in there. If the clutches in the rear are work then you will be fine with out them. The car is relatively new, I would skip them in my opinion. The rest of the parts as described above will be needed for sure
They are the pieces that allow both wheels to push the car instead of just one or the other. You probably don't need them unless you are the brake-torque Burnout King and have worn them out, but you never know.