which car donor can i used fora swap on a 1969 mustang?
are all the 69 mustang came with a 9" rear end
whic is the easy way to find out how many splines my car has?

 

Most 9" rear ends are interchangable. To check for the splines, the easiest way is to pull the axle. Not hard at all, you are going to pull it anyway when you change out that third member. And that is what I would suggest (third member swap). Keep your original third member and get a new one. I got one off ebay for 450 delivered. That way you can have a spare if needed and you don't have to go to a tranny shop, you can do it yourself.

 

Look at your data plate and get the differential number. From codes 1-D the rear will be a standard open rear. And, from codes J-V it will be a locking differential. You have a 28 spline axle because the 31 spline axles didn't come out until 1973. You have an 8" rear. Go to the FAQ to learn all about 9" rears and which donor cars you can use.

 

But if you REALLY want posi-trac youll need to get yourself a chevy 10 or 12 bolt rearend and bolt it up in there.
Now if you want a Traction-Lok rear end youll need to get a Ford 9" rear end.
-P.