Correct numbers for '66 427/390 tranny?

[Tony S.]

I'm trying to discover the correct part numbers for the four speed transmission used on a late 1966 427/390 L36. Can someone tell me the correct numbers for the maincase, side cover and tail housing?

Thanks.
Tony

[Ridge K.]

Re: Correct numbers for '66 427/390 tranny?

[Joseph T.]

Re: Correct numbers for '66 427/390 tranny?

Anthony,
The following is on my 1966 427/390 HP serial # 23,05X (June Car) w/M21 Transmission.
1) Transmission Maincase 3885010
2) Part Number Tag on Cover 3880855
3) Tailshaft 3857584
I hope this information helps you.

[Tony S.]

Re: Correct numbers for '66 427/390 tranny?

Thanks guys. I appreciate the help! I did an archive search before I posted, but the search terms I used didn't give me all of the answers that I was looking for and my 1966 JG doesn't give that info as does the '65 and '67 books.

Best,
Tony

[Joe L.]

Re: Correct numbers for '66 427/390 tranny?

Thanks guys. I appreciate the help! I did an archive search before I posted, but the search terms I used didn't give me all of the answers that I was looking for and my 1966 JG doesn't give that info as does the '65 and '67 books.

Best,
Tony

Tony-----


Your main case and extension housing casting numbers would be the same as Joseph's. The side cover casting should be 3884685.

The transmission part number tag (attached to one of the bolts on the sidecover) would also be the same as Joseph mentioned IF your car also has an M-21 (not all L-36 were so-equipped) AND you have the same rear gear ratio as Joseph's car. Otherwise, a different number would be on that tag.

[Wayne M.]

Re: Correct numbers for '66 427/390 tranny?

Tony-----


The transmission part number tag (attached to one of the bolts on the sidecover) would also be the same as Joseph mentioned IF your car also has an M-21 (not all L-36 were so-equipped) AND you have the same rear gear ratio as Joseph's car. Otherwise, a different number would be on that tag.

Tony -- another casting # to check; the front bearing retainer 3851326.

Joe L. and Tony -- If this tranny has the smaller diameter 8-tooth steel speedo drive gear (on the output shaft), it will probably have sidecover steel tag # 3880853, used on close ratio transmissions that call for plastic speedo driven gears green (22 teeth = 3.70) or yellow (24 teeth = 4.11).

I suspect that Joseph T's tag # 3880855 would be found on a close ratio trans that originally had a 3.08 through 3.55 differential.

[Joseph T.]

Re: Correct numbers for '66 427/390 tranny?

Wayne, My original side case tag was #3880853 and I do have an M21 Close Ratio Trans. with 3:70 Rear end ratio. I was told that this tag was specified for a 327/350 HP (L79) Option.So of course, before the judging process, I replaced it with the specified tag # 3880855. Time to re-install my original Tag.

[Joe L.]

Re: Correct numbers for '66 427/390 tranny?

Wayne, My original side case tag was #3880853 and I do have an M21 Close Ratio Trans. with 3:70 Rear end ratio. I was told that this tag was specified for a 327/350 HP (L79) Option.So of course, before the judging process, I replaced it with the specified tag # 3880855. Time to re-install my original Tag.

Joseph-----


There were many more transmission part numbers than were shown in the AIM's for those years showing part numbers. Also, the reference to engine applications in the AIM, while correct, is NOT ENTIRELY correct or, more specifically, NOT completely inclusive.

The only difference between part numbers for any Muncie variant (i.e. M-20, M-21, M-22) related to the installed speedometer DRIVE and DRIVEN gears. That's it. Otherwise, any given Muncie variant was the same for any given model year (or, range of model years).

The transmission part number GM #3880853 was used for 1966 L-79. That's why it's shown in the AIM for L-79. This is because the L-79 was only equipped with M-21 transmission and the STANDARD rear gear ratio was 3.70:1. So, what is shown in the AIM is the transmission part number for L-79 with STANDARD rear gear ratio (and, possibly, 4.11:1 optional ratio).

The transmission part number shown for M-21 with L-36 is GM #3880855. That's the correct part number for the M-21 with L-36 BUT ONLY IF the rear gear ratio is the STANDARD ratio for that combination of 3.36:1 (and, possibly, the optional 3.08:1 axle ratio).

The transmission used for a 1966 with M-21, L-36, and 3.70:1 rear gear ratio would be EXACTLY the same as that used for M-21, L-79, and 3.70:1 rear gear ratio or GM #3880853.

[Tony S.]

Re: Correct numbers for '66 427/390 tranny?

Hi Joe. I looked up some info in Noland Adams' book, and he shows the '66 L36/M21 having a side cover number of 3880855.

Your thoughts?
Tony

[Wayne M.]

Re: Correct numbers for '66 427/390 tranny?

Hi Joe. I looked up some info in Noland Adams' book, and he shows the '66 L36/M21 having a side cover number of 3880855.

Your thoughts?
Tony

Tony -- I see what you mention in Noland's Vol 2, pg 363. However, as Joe L. has explained, that steel tag # is only appropriate for the STANDARD (or economy) ratio [or any other ratio between 3.08 and 3.55 in the powertrain charts, in the case of '66 427's].

Problem here (and it may have begun with Noland) is that the repro catalogs (Long Island, etc.) have tried to associate a trans tag to a specific engine, whereas it should be linked to 1.) wide ratio, or 2.) close ratio, a)final drives of 3.08 to 3.55, b) final drive ratios of 3.70 and 4.11, or c) final drive ratio of 4.56.

Does't matter what engine, except that choice is limited by the order form / power train charts.

In theory, the L36 could have the same WIDE ratio 4-spd. trans as the base engine 327, as horrifying as that may be to those hoping to verify their rat motor by the trans tag .

[Tony S.]

Re: Correct numbers for '66 427/390 tranny?

Wayne. Just so I'm clear then, what is your opinion as to the correct side cover part number for a '66 L36 car with M21? The '66 JG is NO HELP.

Thanks.
Tony

[John H.]

Re: Correct numbers for '66 427/390 tranny?

Tony -

3880855, per the second-to-last paragraph of Joe's post #8, if you have a 3.08 or 3.36 axle.

[Wayne M.]

Re: Correct numbers for '66 427/390 tranny?

Wayne. Just so I'm clear then, what is your opinion as to the correct side cover part number for a '66 L36 car with M21? The '66 JG is NO HELP.

Thanks.
Tony

Tony -- all '66-7 side COVERS had CASTING #3884685, as does this one on trans from '66 Corvette # 14095.

[ADMINISTRATOR -- I tried to load a pic that I had already used in a previous post and it will not allow the same pic for a different thread --- WHY ?]

But the steel tag attached to the lower forward sidecover bolt will be stamped 3880855 if ratio 3.08 - 3.55, and 3880853 if 3.70 or 4.11.

[Joe L.]

Re: Correct numbers for '66 427/390 tranny?

Hi Joe. I looked up some info in Noland Adams' book, and he shows the '66 L36/M21 having a side cover number of 3880855.

Your thoughts?
Tony

Tony-----


Are you talking about the side cover CASTING number or the transmission assembly PART NUMBER TAG which is attached to one of the side cover bolts?

If it's the CASTING number, that would be GM #3884685 for a 1966 Muncie. If it's the transmission assembly PART NUMBER TAG, that would be 3880855 IF it's an L-36 with M-21 and STANDARD rear gear ratio of 3.36:1 (or, possibly, the optional ratio of 3.08:1)

[Michael H.]

Re: Correct numbers for '66 427/390 tranny?

Tony -- all '66-7 side COVERS had CASTING #3884685, as does this one on trans from '66 Corvette # 14095.

[ADMINISTRATOR -- I tried to load a pic that I had already used in a previous post and it will not allow the same pic for a different thread --- WHY ?]

But the steel tag attached to the lower forward sidecover bolt will be stamped 3880855 if ratio 3.08 - 3.55, and 3880853 if 3.70 or 4.11.

Joe and Wayne are correct. There was an extensive discussion right here on this topic a few years ago and the reason why there seems to be no listing for the M21 with 427/390 HP and 3.70 is that there was an error in the AIM AND the 66 parts book.
According to the 66 AIM, there is no such thing as a 427 390 HP with M21 and 3.70 diff. but we know that's not the case.
The transmission for that application is the exact same as a 350 HP 327 with 3.70 diff, just as Joe mentioned.
My 66 is a 427 with M21 and 3.70 and the tag shows a 3880853.