# '66 differential?



## Cross's 66 (Nov 7, 2015)

Hi Folks; I was hoping that someone could tell me what gears I have or even if I have an original GTO differential. The numbers I have on the differential do not match anything that I have found on the web. With my bad eyes it looks to be "J4 6" with "9788393". 

Any help would be greatly appreciated!

Cheers


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## GTOJUNIOR (Aug 7, 2011)

It is a '66 but you need to locate the two letter code that should be on the RH axel tube to see what gear set was installed originally, 
right of the vent on the rear facing out on tube is where they are commonly stamped.


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## 05GTO (Oct 6, 2004)

How many teeth do you have on the ring and pinion gears?


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## GTOJUNIOR (Aug 7, 2011)

The one shown above was a 3:55 
My '66 with AC has a 3:23 
here it is before re-assembly many miles ago, don't recall tooth count.


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## Cross's 66 (Nov 7, 2015)

Hey guys, thanks very much for your help. Those alpha codes are small, I think I may have gone right over them without noticing! I did count the gear teeth and came up with 42 and 13; 3.23 ratio?


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## Cross's 66 (Nov 7, 2015)

I guess my other question would have to be around the type of rear-end. Is it a posi or not?


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## Pinion head (Jan 3, 2015)

Oem 8.2 Pontiac Safe-T-Track (posi) carrier. All oem Pontiac 8.2 STT carriers were cone type, hopefully cones have not bottomed out and carrier is no longer tight. If considerable wear on the cones will need disassembly, machining, shimming up, and reassembly.


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## Cross's 66 (Nov 7, 2015)

Hi PH, thanks very much! Unfortunately as a real dummy/newbie, I really dont know what you mean by cone type? How do I tell if they are bottomed out and need machining? Regards


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