Wilson

I am looking at a 12 bolt 3:91 posi to put under my '65. It is code
stamped TO. Can you tell me what this came out of? Thanks, Wilson

svnt442

All depends. It's an A-body type-O axle so it came in an Olds A-body from 68-70. You're going to need a date code to figure out what year it is because they changed the bearings and axles in 1970.

2blu442

My reference book from Supercarsunlimited shows the TO code for the 3.91 Type O rear end was used in 1967,68,69. The type O has a round inspection cover with 12 bolts holding it on. These were used in 442's, W30's and Hurst Olds (68-69) but I imagine a Cutlass could have been ordered with one too. That's a hard to find part and if the price is right well worth snapping up! John

svnt442

Thanks for the clarification John.

Wilson

Thanks guys for your help!

Wilson

Ok, I bought the code TO 3:91 posi. Can you tell me what it's worth so I'll know if I did ok?

Also, my buddy who is a chevy guy at heart, but has a fondness for olds too is concerned that it will not be strong enough for my motor and thinks I should go with a chev 12 bolt. Your thoughts? Wilson

2blu442

If its in nice condition $750 to $1,000 may be a going rate. No worrys about strength, the Chevy 10 bolt of the 1960's is much weaker than this Olds 10 bolt that you purchased. I believe the Chevy 10 bolt uses 27 spline axles with a 8.2 inch ring gear. Then the type O TO 3.91 you purchased uses a 31 spline axle on an 8.5 inch ring gear. The Chevy 12 bolt used a 30 spline axle on an 8.75 ring gear. I consider both 507OLDS and monzaz as guru's when it comes to differentials and rear ends. You can check with them if you have any doubts. If you have time you might try the search option as I know this topic has come up before. John