Rear diff options?

Old Oct 20, 2011 | 10:58 AM
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Rear diff options?

What were all the diff options available in a 1971 Supreme? Could mine be a flange axle 10 bolt 8.5" 28 spline? Thanks Ryan
Old Oct 20, 2011 | 11:24 AM
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Originally Posted by onetogofast
What were all the diff options available in a 1971 Supreme? Could mine be a flange axle 10 bolt 8.5" 28 spline? Thanks Ryan
Yup, otherwise known as a corporate 10 bolt, or it could be a 12 bolt depending on the series

Are you asking what gears were available?

Have a look through this link, it should help you. Feel free to join Wild About Cars - it's free and has lots of good info. That's where this CSM excerpt came from http://wildaboutcarsonline.com/membe..._Section_0.pdf
Old Oct 20, 2011 | 12:28 PM
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Thanks!!!
Old Oct 20, 2011 | 01:05 PM
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You're welcome.
Nice pic of your 71. Not bad pic of your wife too! I remember when that car was new, and when I used to be able to kiss like that...

You should consider starting a photo gallery on your profile page.
Old Oct 20, 2011 | 01:40 PM
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LOL thanks! Yeah they're both in really good condition.
Old Oct 22, 2011 | 04:19 AM
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All of the 71-72 Cutlass/442's came with the 8.5" 10-bolt,with bolt-in axle,no c-clips.Those are great rears,and there are plenty of parts available for them.
Old Oct 22, 2011 | 05:05 AM
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That's good, the open 2.56 option needs to go LOL
Old Oct 22, 2011 | 10:31 AM
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I was interested in this also, checking out Allan R's link as i type
All i know about my 72' Supreme's rear is it is a 10-bolt and has posi. Dont know if open rear or posi made a difference on what gears were in it but itd be nice to have a guess as to what is in there (build sheet is long gone). Also its backing a 4-barrel 350
Old Oct 22, 2011 | 10:55 AM
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Originally Posted by Vega
I was interested in this also, checking out Allan R's link as i type
All i know about my 72' Supreme's rear is it is a 10-bolt and has posi. Dont know if open rear or posi made a difference on what gears were in it but itd be nice to have a guess as to what is in there (build sheet is long gone). Also its backing a 4-barrel 350
The 72 350 4bbl 442 posi would have had 3:23 gears. The taller gears 3:42s went with the 455/400
Old Oct 22, 2011 | 11:04 AM
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Originally Posted by Allan R
The 72 350 4bbl 442 posi would have had 3:23 gears. The taller gears 3:42s went with the 455/400
Is that the only posi rear end they matched up with the 350 4-barrel? Mines in a Supreme so im not sure if it was the same as the 442 350 or not. Ive been trying to find the ID on the rear axle but im not exactly sure where to look, the wildaboutcars link has a lot of good info but the pic showing where to find the codes is pretty vague.

Id be happy with 3:23 though, thats actually exactly what i was going to try to get into the rear if it didnt have this. So thatd be awesome
Old Oct 22, 2011 | 01:39 PM
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Originally Posted by Vega
Is that the only posi rear end they matched up with the 350 4-barrel? Mines in a Supreme so im not sure if it was the same as the 442 350 or not. Ive been trying to find the ID on the rear axle but im not exactly sure where to look, the wildaboutcars link has a lot of good info but the pic showing where to find the codes is pretty vague.

Id be happy with 3:23 though, thats actually exactly what i was going to try to get into the rear if it didnt have this. So thatd be awesome
No, it's not the only set of gears you could get with a posi. It's what Olds put standard if you ordered the 442 option in 72. There were other ratio's available including 2:56, 2:73, 2:93 and 3:08.

If you really want to know what your gear ratio is, jack up both rear wheels of your car. Index one wheel with a white mark. Index your drive shaft with a white mark. Have a friend slowly rotate the tires while you count the number of times the drive shaft rotates. If he turns the wheel 10 times and you count 32 and a bit, it's the 3:23. This method takes away some of the guess work of only rotating the wheel once.
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