68 rear end cover & spring

[Nick P.]

Hello

The stamp on my differential is 1AU1 9 68w, which i believe is Jan. 9 68.Would a cover with L 14 7, which I believe is dec. 14 67 be correct?My cover presently has a heavy duty unit and I've found one with this date.Also should my spring be 2.25",and when did the springs increase to 2.5"?

[Wayne M.]

L-14-7 = 1977, not 1967 ....

I assume we're talking about a # 3781375 diff cover. Dating (near the filler plug flange) didn't start until sometime in 1969 [I believe Joe L. has said his original-owner '69 does not have a date]. Not certain, but the wider spring was introduced about the 1976 -77 era

[Wayne M.]

L-14-7 = 1977, not 1967 ....

I assume we're talking about a # 3781375 diff cover. Dating (near the filler plug flange) didn't start until sometime in 1969 [I believe Joe L. has said his original-owner '69 does not have a date]. Not certain, but the wider spring was introduced about the 1976 -77 era

[Joe L.]

Re: 68 rear end cover & spring

Nick-----

The cover would be a very acceptable date for your differential unit.

All 1963-77 Corvettes use a 2-1/4" wide spring. After 1977, both 2-1/4" and 2-1/2" were used depending upon application.

[Joe L.]

Re: 68 rear end cover & spring

Nick-----

The cover would be a very acceptable date for your differential unit.

All 1963-77 Corvettes use a 2-1/4" wide spring. After 1977, both 2-1/4" and 2-1/2" were used depending upon application.

[Dick W.]

Re: 68 rear end cover & spring

I do not believe that it is possible to judge this date code installed on the car while it is sitting on the ground. Would have to have some nano robotic judges. Even shorter than Carlton

[Dick W.]

Re: 68 rear end cover & spring

I do not believe that it is possible to judge this date code installed on the car while it is sitting on the ground. Would have to have some nano robotic judges. Even shorter than Carlton

[Joe L.]

Re: L-14-7 = 1977, not 1967 ....

Wayne and Nick-----

Yes, I used to think that the 3871375 cover dating did not begin until very late 1969 and my September, 1969-built car has a cover with no dates. However, now I'm not so sure that some covers might not have been dated prior to that. Nick's situation helps to confuse me. Here's why: the GM casting #3871374 cover was last used in PRODUCTION for the 1977 model year. So, none of these covers were ever used on a car after August, 1977.

The covers remained available in SERVICE for awhile, although I would expect that the SERVICE inventory was manufactured prior to the end of the use for PRODUCTION. After the SERVICE inventory was depleted, the 78-79 cover, GM #464909 (casting 464910), became the SERVICE cover for all 63+ Corvettes.

This cover is dated December 1967 or 1977. If it does denote 1977, then it must be that the cover was still being manufactured after its PRODUCTION use ended. This is possible but, I think, unlikely.

So, I really don't know what the deal is here. Maybe the best thing for Nick to do would be to look for an undated cover. There should be plenty of them around. That is, if he still thinks that dates for this piece are important. As Dick mentioned, they can't really be seen on the judging field.

[Joe L.]

Re: L-14-7 = 1977, not 1967 ....

Wayne and Nick-----

Yes, I used to think that the 3871375 cover dating did not begin until very late 1969 and my September, 1969-built car has a cover with no dates. However, now I'm not so sure that some covers might not have been dated prior to that. Nick's situation helps to confuse me. Here's why: the GM casting #3871374 cover was last used in PRODUCTION for the 1977 model year. So, none of these covers were ever used on a car after August, 1977.

The covers remained available in SERVICE for awhile, although I would expect that the SERVICE inventory was manufactured prior to the end of the use for PRODUCTION. After the SERVICE inventory was depleted, the 78-79 cover, GM #464909 (casting 464910), became the SERVICE cover for all 63+ Corvettes.

This cover is dated December 1967 or 1977. If it does denote 1977, then it must be that the cover was still being manufactured after its PRODUCTION use ended. This is possible but, I think, unlikely.

So, I really don't know what the deal is here. Maybe the best thing for Nick to do would be to look for an undated cover. There should be plenty of them around. That is, if he still thinks that dates for this piece are important. As Dick mentioned, they can't really be seen on the judging field.

[Donald T.]

Re: L-14-7 = 1977, not 1967 ....

Not sure how plentiful undated 375 rear covers are. I've been watching ebay for months and haven't seen one. My 4th edition 65 JG states that rear covers were dated in 65. Of course the JG may not be correct. I finally gave up and got a HD rear cover from Muskegon Brake. My project for today is to install it. Heated garage but man that concrete floor is cold!!!

[Donald T.]

Re: L-14-7 = 1977, not 1967 ....

Not sure how plentiful undated 375 rear covers are. I've been watching ebay for months and haven't seen one. My 4th edition 65 JG states that rear covers were dated in 65. Of course the JG may not be correct. I finally gave up and got a HD rear cover from Muskegon Brake. My project for today is to install it. Heated garage but man that concrete floor is cold!!!

[Wayne M.]

Easy to mis-read '65 JG ...

I've got 3rd ed., and unless it's been re-worded in the 5th ed., The "Reference:" paragraph (written in italics) says ... "The casting number is 3871375, which is located on the rear of the COVER." (caps are mine)

Next sentence (which should at LEAST be in another paragraph) reads: "The casting date is located just below the driver side output flange." This sentence is now referring to the CARRIER, not the COVER.

I hope this phraseology has not resulted in many swap-outs of original rear differential covers. Would be interested to hear if '66/'67 tech manuals read the same.

[Wayne M.]

Easy to mis-read '65 JG ...

I've got 3rd ed., and unless it's been re-worded in the 5th ed., The "Reference:" paragraph (written in italics) says ... "The casting number is 3871375, which is located on the rear of the COVER." (caps are mine)

Next sentence (which should at LEAST be in another paragraph) reads: "The casting date is located just below the driver side output flange." This sentence is now referring to the CARRIER, not the COVER.

I hope this phraseology has not resulted in many swap-outs of original rear differential covers. Would be interested to hear if '66/'67 tech manuals read the same.

[Donald T.]

Re: Easy to mis-read '65 JG ...

Wayne, I'm working off the 4th ed. so I can't speak to the 5th. The verbiage in the 4th is the same as you describe. Perhaps the 5th edition has updated that section. Anyway I just completed the installation of a replacement rear cover. I gave up on trying to find an undated 375. Can't really see the difference when the spare tire assembly is installed anyway

[Donald T.]

Re: Easy to mis-read '65 JG ...

Wayne, I'm working off the 4th ed. so I can't speak to the 5th. The verbiage in the 4th is the same as you describe. Perhaps the 5th edition has updated that section. Anyway I just completed the installation of a replacement rear cover. I gave up on trying to find an undated 375. Can't really see the difference when the spare tire assembly is installed anyway