2003 Mustang Gt Rear End
 

Hey, just the other day, i completely destroyed my spider and side gears in my 03 gt. I would like to convert my 28 spline rear to a 31 spline. Why is it that is says in the product info on the 31 splined spider gears http://www.latemodelrestoration.com/item/LRS-4215B that is this not the cheap way to convert a factory 28 spline rear end to a 31. How is that not cheaper? for one, the 28 splined spider and side gears are $144. I already planned on buying the Moser 31 splined axles and everything to convert over but the price of a new differential was holding me back. I have to buy new clutches anyways becuase they are destroyed too. theres not much more that i have switch, the car has reletively low miles so the bearings should be just fine.I know that there are the rear end kits that come with the differential carrier, and axles and studs but i dont need a new carrier and i dont feel like taking the whole rear end out and have to shim and center the ring and pinion when i can just change everything around that. what are your thoughts?

It seems that the 31 spline carrier is a different size, in order to accommodate the larger diameter axles. If using an OEM carrier, I bet you can get away w/ running the shim pack you have for the pinion and diff (though you should measure it to be sure).

You need a new diff, not just the spider gears. I'd stick with 28 spline axles unless you're making ridiculous power. 28spline aftermarket axles are more than sufficient for most uses. Get the bearing kit, you can't tell what's broke till you tear it apart.

im not sure how much horsepower im gettin to the rear wheels. and i figured since im already in there i can just switch them around with new 31 spider and sides. I drag race this car n since all this happened, i was planning up building it up anyways. Everything else seemed fine inside when i opened it up, ring and piniion had no damage and the bearings didnt show any sign of damage. i just REALLY didnt feel like taking the whole differential out and have to reshim the ring and pinion. but i figured i would ask before i did anything, if u have anymore thoughts let me know!

replace the carrier. If you're going to build it to beat on it don't fuck off the keystone.

if you replace carrier you only have to reshim it, the pinion can be left alone. Go with Ford motorsport 31 spline carrier with C on the part number, it has carbon discs and is rated at high HP level, same discs used in 03-04 cobra I believe.

+1 for what he said above. That or add 2 extra clutches to make it grab harder.

If you want a low cost 31 spline carrier, just get the limited slip differential out of a F150 or van with an 8.8 and pack the clutches tighter like spike mentioned. Get a set of Moser 31 spline axles and you'll be straight.