ClassicOldsmobile.com - View Single Post - Questions for '71 Cutlass Supreme differential

monzaz · 09-04-2007, 08:17 AM

There are axle tube stamped numbers and letter suffixs on the passenger tube. BUT being that the cars is so old that is not the best way to tell. esspecial if someone repaired it over the years...never can tell.

BEST ALWAYS TO CRACK OPEN THAT COVER .Spin and wipe the ring gear outer edge diameter untill you find the ring gear and pinion gear tooth count like 16 41 or 15 41 divide the smaller pinion gear into the larger ring gear number and you will get your ratio. round up the 2nd digit after the decimal .

example ( 15 41 comes out to 2.7333333333) so no round up
example (13 40 comes to 3.07692307692 ) round up because of the 6 to 3.08...hope that helps. Jim

Oh and use it, as long as you get a good aftermarket Anti Spin (limited slip diff unit) or short LSD industry standard name for positraction/anti spin/ trac lok/suregrip etc. the rear will hold up very well. It is a 8.5 rear in 1971 1972 years. Good luck and if you need a quote on parts give us a shot at some prices. Jim

jdrace.com

09-04-2007, 08:17 AM	#7 (permalink)
monzaz Senior Member Join Date: Jul 2006 Location: Richfield, Oh Posts: 101	IDing rears There are axle tube stamped numbers and letter suffixs on the passenger tube. BUT being that the cars is so old that is not the best way to tell. esspecial if someone repaired it over the years...never can tell. BEST ALWAYS TO CRACK OPEN THAT COVER .Spin and wipe the ring gear outer edge diameter untill you find the ring gear and pinion gear tooth count like 16 41 or 15 41 divide the smaller pinion gear into the larger ring gear number and you will get your ratio. round up the 2nd digit after the decimal . example ( 15 41 comes out to 2.7333333333) so no round up example (13 40 comes to 3.07692307692 ) round up because of the 6 to 3.08...hope that helps. Jim Oh and use it, as long as you get a good aftermarket Anti Spin (limited slip diff unit) or short LSD industry standard name for positraction/anti spin/ trac lok/suregrip etc. the rear will hold up very well. It is a 8.5 rear in 1971 1972 years. Good luck and if you need a quote on parts give us a shot at some prices. Jim jdrace.com Last edited by monzaz : 09-04-2007 at 10:11 PM.