I have a 99 GT. Im trying to find out if I have a limited slip(with posi) or not and what my spline count is(28 or 31). I read somewhere that there is an axle code on the data plate( my code was LE). When i checked the list of codes mine was not there. Im planning on putting 3.73s in and so i figure while Im in there might as well do the diff too. Thanks for the help.

 

Factory rear ends are 21 spline unless you have a Cobra or GT-500. If you have traction control older Fords had a weird limited slip type rear, you may want to call a ford dealer and confirm or call Ford 800-788-FORD. If you have limited slip then get Cobra clutch pack when you do gears.

 

Your 99 GT has 28 spline axles/diff. All Ford 8.8 L.S. diffs (86-current) are basically the same. Difference is 28 or 31 spline and the newer ones come with carbon fiber clutch plates.

You can look at the r.r. and see a tin tag ( held on with one of the cover bolts) It should say something like 3L 08 .......limited slip with 3.08 gears.

Casey