63 diff
Le Mans Master
Joined: Jan 2000
Posts: 8,918
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From: New Hill NC
Team Owner
Joined: Nov 2005
Posts: 28,180
Likes: 2,872
From: Beach & High Desert Southern California
The codes can be different for separate years but I believe 66' & 67' use the same coding (from http://www.corvette.net/tech-6.htm):
2A09 9 67
2 = ? (maybe a rebuilder's stamp)
AO = 3.70 ratio
9 9 67 = September 9 1967 assembly date
There is also a housing casting date on the drivers side ahead of where the leaf spring mounts.
It's from a 67'
Thread Starter
Racer
Joined: Jan 2008
Posts: 291
Likes: 17
From: Woodinville Wa
I am sure you are right that it is a 67.I bought the car in 1969,Why it was changed out I do not know.What would the different between a 63 and a 67 diff.I feel bad that is not the orginal diff but at least I know now....Thanks .....Vince
Tech Contributor
Joined: Aug 1999
Posts: 15,156
Likes: 3,965
From: Connecticut, USA
The 63's had poor posi's and often blew out under load. In 65 they switched to the much better eatons. The 67 if original, given the history probably is, was most likely new or near new at the time to replace a wrecked 63 unit. It was faster to install a complete 67 diff then rebuild the 63 and back in '68-69 used corvettes were about $1800.
The 67 posi is better but the case is not as good as the late 69-79 cases. The clutches are the much better solid steels. The spiders are the weaker 10-18's.
The 67 posi is better but the case is not as good as the late 69-79 cases. The clutches are the much better solid steels. The spiders are the weaker 10-18's.
Thread Starter
Racer
Joined: Jan 2008
Posts: 291
Likes: 17
From: Woodinville Wa
You are right in 69 I paided $1800 for my 63.Thank for the information on the 67 diff at least I feel a little better.I just rebuilt the trailing arms,replaced the strut assembly and install a new stock leaf.I was going to pull the diff out ,but that will be another time.It seems to be working OK ,but I will keep a eye on it.Thanks again for all the information that I have gotten on this forum.....Vince
Le Mans Master
Joined: Feb 2000
Posts: 7,032
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From: Newburgh NY
Gary pretty muched summed it up for you but below is a pic of an original 63 case and stamp. Two things to note that if you wanted to get an original 63 case (I got one for another 63 from Ikerds) and put a newer Eaton Posi unit in this can be done. I did it with mine as the whole posi unit was in pieces when I pulled it apart.
Also note that if you plan to get the car judged at anytime, they ussually don't even get under there and check the numbers although it's in the judging guide. In many cases, when judged, the car is not even on a lift.
But, if you just plan to continue to drive and enjoy the car as you have for 40 years!!! leave it alone because what you have is good to go!
Also note that if you plan to get the car judged at anytime, they ussually don't even get under there and check the numbers although it's in the judging guide. In many cases, when judged, the car is not even on a lift.
But, if you just plan to continue to drive and enjoy the car as you have for 40 years!!!
leave it alone because what you have is good to go!
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Le Mans Master
Joined: Feb 2000
Posts: 7,032
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From: Newburgh NY
As far as your 67 goes, as someone else noted, if it is actually "AO", then it would have originally been a 3.70 if no one changed gears in it.
You can figure it out by marking the driveshaft and a spot on the tire and turning the wheel (in neutral with car jacked in the air, on JACKSTANDS) and watching how many revolutions the driveshaft does. Or figure out how many RPMS at what MPH in what Gear the car does.
Race Director
Joined: Jul 2005
Posts: 13,685
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1963 and early '64 diffs mount to the frame with two bolts that thread into the mount from opposite sides. Late '64 - up diffs use one long bolt and a nut.
Dick Guldstrand didn't believe me when I told him about the two bolts on my '64 (#1653). He did after pulling it to change replace my Posi with a heavy-duty Tom's unit! Guess the mounting was a running change that didn't coincide with the model year.
Dick Guldstrand didn't believe me when I told him about the two bolts on my '64 (#1653). He did after pulling it to change replace my Posi with a heavy-duty Tom's unit! Guess the mounting was a running change that didn't coincide with the model year.