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10 bolt GM rear end codes?

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81K views 11 replies 6 participants last post by  big gear head  
#1 ·
WHere can I find the code on a 10 bolt GM rear end and will this code tell me the gear ratio on the inside?
I appriciate any help I can get thanks everyone!!
 
#4 ·
1 more for now

Another question would be do you know a site where I could find out exactly from the code what rear end it is and the specs on it ( gear ratio) its a 12 bolt as well and also is the correct number just one letter and than 2 numbers?

the numbers I found are...(D26)(GM72)and(3896339 with the letter N underneath the numbers) Thanks again by all means!!
 
#5 · (Edited)
303oldskool said:
Another question would be do you know a site where I could find out exactly from the code what rear end it is and the specs on it ( gear ratio) its a 12 bolt as well and also is the correct number just one letter and than 2 numbers?

the numbers I found are...(D26)(GM72)and(3896339 with the letter N underneath the numbers) Thanks again by all means!!
Those look like the #'s off the center section. What does the rear cover look like? Round for a car or Pear/Apple shaped for a truck?
D-2-6= April 2nd 1966
3896339 = casting #??
GM72 = nothing important
The Axle code is on the passenger side front of tube, will be 2 letters, #'s & a letter. Something like this CX 0727 B >>
ProStreet6t9 may know what casting # that is.
 

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#6 ·
The ratio code is usually two letters (sometimes 3, sometimes a number & 2 letters), and is found on the right-hand axle tube. The code will tell you what was originally installed in the housing, but nothing about any changes that might have been made since then.

You'd be better off checking the true ratio either manually, or by popping the cover and looking on the edge of the ring gear for four sets of numbers, two of which are tooth counts and two of which are date codes.
 
#7 ·
303oldskool said:
Another question would be do you know a site where I could find out exactly from the code what rear end it is and the specs on it ( gear ratio) its a 12 bolt as well and also is the correct number just one letter and than 2 numbers?

the numbers I found are...(D26)(GM72)and(3896339 with the letter N underneath the numbers) Thanks again by all means!!
I looked for that cast number and I'm not having any luck YET, It is a 12 bolt car correct? Did you find any other numbers on the axle tube?

Are you just wanting the Ratio or Wanting to know what the housing came out of originally?
 
#8 ·
303oldskool said:
Another question would be do you know a site where I could find out exactly from the code what rear end it is and the specs on it ( gear ratio) its a 12 bolt as well and also is the correct number just one letter and than 2 numbers?

the numbers I found are...(D26)(GM72)and(3896339 with the letter N underneath the numbers) Thanks again by all means!!
Double check that casting number to make sure it's correct, I think the D26 is for a 1966 housing as SSedan stated. I cant find any 66 12 bolt car's with that casting number.
 
#9 ·
Im not sure really its actually in my K5 and im not finding any numbers any where else I think im just gonna go ahead and pop the rear cover off and go that route for sure? thanks very much for your guys help as well

another ? I had is I have heard of a way of counting the driveshafts rotations when having the rear end jacked up and spinning the rear wheels slowly?
Do you guys know of anything like this? I guess there is some math involved with it to get the correct ratio?
If you do how would I go about doing that?
 
#10 ·
303oldskool said:
Im not sure really its actually in my K5 and im not finding any numbers any where else I think im just gonna go ahead and pop the rear cover off and go that route for sure? thanks very much for your guys help as well

another ? I had is I have heard of a way of counting the driveshafts rotations when having the rear end jacked up and spinning the rear wheels slowly?
Do you guys know of anything like this? I guess there is some math involved with it to get the correct ratio?
If you do how would I go about doing that?
Then it's definitly not a 66 housing,my bad! If you don't know the history of the diff, it would be a good idea to at least change the oil. I would pull the cover and verify the ratio.