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Hi.
Can anybody advise if the codes "40 13 GM 965 XO" in the rear diff (66 GTO)
bear any relevance to the axle ratio? If so what ratio would they make it. Or are they just factory part stamps.
I am a new member from the UK. (not many goats over here).
Many Thanks.
 

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3,523 Posts
Hi.
Can anybody advise if the codes "40 13 GM 965 XO" in the rear diff (66 GTO)
bear any relevance to the axle ratio? If so what ratio would they make it. Or are they just factory part stamps.
I am a new member from the UK. (not many goats over here).
Many Thanks.
If it's a true '66 axle, look on the back of the axle tube, passenger side for a "stamped" 2 letter code. Should begin with a w, x, y or z. The x codes were XE, XF, XG and XH. No XO. Could it be an XG? The code will tell you the ratio and whether or not it was a posi.
 
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