Where is the cast date code on C3 differential
I have another open post looking for trans and differential info, but I was wondering where the cast date is on the differential housing? Is it easy to get at and read?
Thanks,
Joe
Thanks,
Joe
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Re: Where is the cast date code on C3 differential
It's right here on my 69. The pic was taken from where the battery would be if the body was on. -
Re: Where is the cast date code on C3 differential
Greg, Thanks, I will have to get it back into the air to see that.
JoeComment
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Re: Where is the cast date code on C3 differential
Greg, Thanks I got it G 3 8. I would assume that to be July 3rd, 1968, except for the stamping on the bottom O A W 1 9 8 E 3, I belive the first digit to be an O, but might be a C, but it looks like the line connects. Can you decode that? I checked the tire rotation/gear ratio and I believe the gears to be 3.08. I am now pretty sure this is not the original differential and the car has a 7 leaf rear spring with no rear stabilizer. The car has the original 350/350 engine and trans (I now believe it to be an M20).
Thoughts?Comment
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Re: Where is the cast date code on C3 differential
Assuming the "O" in "OAW198E3" is a "C", which is what it probably is, that denotes a CAW rear, meaning 3:08 Positraction big block rearend. I'm pretty sure that rear swaybars weren't an option on small block cars, only big blocks. Look and see where each halfshaft U-joint is on the rear diff's side yokes; Big Block & LT-1 rears have caps with straight bolts holding the u-joints in the yoke. Small block cars all had plain u-bolts holding them on. I'm guessing at the date here....198E3 would be, I GUESS, January (1) 9th day (9) 1968 (8) Eaton Axle Plant (E) 3rd shift (3)......my guess is, if you know your motor/trans are original, somebody probably dumped the clutch at 7 grand, grenaded the original rearend and grabbed the one you have as a donor, or warranty replacement did you a favor and gave you a BB rearend, etc.....or make sure you don't have a small block combo in a big block car!Comment
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Re: Where is the cast date code on C3 differential
Jeremy, Thanks. I am 100% on the small block. The engine stamp and the tranny stampings match vin and the cast dates are correct also. So, I think I have a 3.08 big block diff, but I did not check to see if it was a positraction rearend. My book indicates that you could get the sway bars with the F41 suspension option, but since I have zero paperwork with the vehicle I have to assume the rear end has been changed. The stamping is strange though because the housing cast date is july 3rd, which is before jan 9th. I cover has a stamping of 464910, which I have been told was used in 1978.
Still more confusion.Comment
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Re: Where is the cast date code on C3 differential
The rear assembly stamping uses a julian calendar date. Should be the 198 th calendar day, Eaton plant, 3rd shift.Comment
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Re: Where is the cast date code on C3 differential
Dump the clutch at 4500....if you have one tire smoking, you have an open rearend LOL!!! Honestly, at least from what I've had and seen, rearends get replaced nearly as much as engines in these cars, especially the higher horse cars. I had a '70 LT-1 that had a '74 rearend in it, replaced by the dealer it came from. I'm sure a LOT of others have similar stories. As far as judging, you're screwed because of the big block caps on the outer yokes-dead giveaway that it was replaced, as the only small block cars that had those were LT-1's, from '70-'72. Judges can't see the diff code, but the can see the caps and the casting date. But if you're not doing the judging thing.....have fun seeing if you have Posi or not!!!!!
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Re: Where is the cast date code on C3 differential
The caps on the inboard yokes also came on ALL M40 Corvettes. I really wish people would stop calling them big block rear ends. There are probably more small blocks with caps on the side yokes than big blocks.TerryComment
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Re: Where is the cast date code on C3 differential
Sorry....I just figured since the lad stated he thought he had an M20, the idea of the car being an M40 auto was moot, so I guess I kinda disregarded it. I will humbly accept the official NCRS punishment of forty lashes to the back with a parking brake cable, and a driveshaft to the head for that mistake.....I'll take one for the team! LET THIS BE A LESSON FOR THE REST OF YOU!!!!
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Re: Where is the cast date code on C3 differential
Thanks everyone. From all of this, I know I have a 3.08 gear ratio, yet to spin the tires and check if it is posi. I still do not know what the date code really is, maybe 68, maybe 78 or julian date of 198th day, but what yr? Again the casting is G 3 8. Also all the talk of caps vs u bolts, well I have u bolts, not caps as someone earlier stated, although the other part of the stamping makes the diff appear to be from a big block car. I do have a 7 leaf rear sping, with no stabilizer. The half shafts are 2 1/2" dia.
I am not going to have the car judged, just attempting to document what I have and get a few items that are either broken or missing put back into operation.
The item that started my 2 posts was my speedo is reading low. I wanted to know which speedo gear I needed. The previous owner told me the car had an M21 with a 3.70 posi, which I now know to be incorrect.
Anything else I should know?Comment
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Re: Where is the cast date code on C3 differential
No lashes Jeremy -- I'm just venting.
I can only speak for 1968-1972 regarding the heavy duty differential with M40. I don't know about the other M40 applications.TerryComment
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Re: Where is the cast date code on C3 differential
A lot of the rear ends were changed in rebuilding. You should probably check the rear by counting the revolutions of the drive shaft and not go by the stamping on the rear.Comment
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Re: Where is the cast date code on C3 differential
Bob,
Thanks, earlier in my post I mentioned that I did that. I checked it 3 times. For 1 tire revolution I get just over 3 revolutions of the drive shaft. So, that is why I believe it to be a 3.08.
I will take a pic of the stamping next time I get the car in the air and post it and see what everyone thinks.
This all leads back to my other post as I am trying to get me speedo to indicate the correct speed.
JoeComment
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