66 Muncie differences 3880853/3880855

[John H.]

Re: 66 Muncie differences 3880853/3880855

The only thing that differentiated one Muncie from another (within the M20 family or within the M21 family) to get a different part number (tag) was the installed DRIVE gear ("large" or "small", depending on intended axle ratio spread). The adapter and DRIVEN gear were installed at the car assembly plant, to match the axle ratio.

[Ronald L.]

Re: 66 Muncie differences 3880853/3880855

John,

That is exactly what I recall, seems strange they did not write those pages and release the part numbers as just one M21 and a list of drive gears depending upon usage; ditto for the M20 and M22.

The conflict remains, L36 and 3.70 gear, use a 853 or 855?

All depends on the page in the AIM you look at or do you have better insight into this?

[Michael H.]

Re: 66 Muncie differences 3880853/3880855

John,

That is exactly what I recall, seems strange they did not write those pages and release the part numbers as just one M21 and a list of drive gears depending upon usage; ditto for the M20 and M22.

The conflict remains, L36 and 3.70 gear, use a 853 or 855?

All depends on the page in the AIM you look at or do you have better insight into this?

There was an in depth discussion on this topic about two years ago. The errors are in the AIM and a 1966 printing of the parts book.
Search the archives for the part numbers 3880853 and/or 3880855.

[Joe L.]

Re: 66 Muncie differences 3880853/3880855

The only thing that differentiated one Muncie from another (within the M20 family or within the M21 family) to get a different part number (tag) was the installed DRIVE gear ("large" or "small", depending on intended axle ratio spread). The adapter and DRIVEN gear were installed at the car assembly plant, to match the axle ratio.

John------


In that case, I don't understand why there were more than 3 part numbers (or, 6 if M-22 was included).

The M-20 would have only required 1 DRIVE gear (and, 1 part number) since it was never available with anything numerically higher than 3.55:1. The M-21 would have required both DRIVE gears (and, 2 part numbers) depending upon rear axle ratio. The M-22 would have required both DRIVE gears and a special DRIVE gear for 4.56:1 (and 3 part numbers).

[Wayne M.]

Re: 66 Muncie differences 3880853/3880855

John------


In that case, I don't understand why there were more than 3 part numbers (or, 6 if M-22 was included).

The M-20 would have only required 1 DRIVE gear (and, 1 part number) since it was never available with anything numerically higher than 3.55:1. The M-21 would have required both DRIVE gears (and, 2 part numbers) depending upon rear axle ratio. The M-22 would have required both DRIVE gears and a special DRIVE gear for 4.56:1 (and 3 part numbers).

I agree, Joe; given the info on the power train charts and the 1966 Corvette dealer order form. There are many part numbers in Ronald's '66 AIM tables that don't make sense, and they may just be errors as Michael Hanson has mentioned.

To answer Ronald -- L36 with 3.70 takes the '853' tag; the reason the UPC M20/21/22 table shows '855' is because the power train chart shows 3.36 axle as the 'General Purpose' (standard) ratio for the close ratio 4-speed trans. The 3.70 is the 'Mountain' ratio for the 390hp with the close ratio trans. Likewise for the L72; standard axle was 3.55, with 3.36 also available under the '855' trans tag, and 3.70 and 4.11 available with the '853' trans. In 1966 you needed to order the L88 to get a 4.56 axle from the factory.

[Joe L.]

Re: 66 Muncie differences 3880853/3880855

I agree, Joe; given the info on the power train charts and the 1966 Corvette dealer order form. There are many part numbers in Ronald's '66 AIM tables that don't make sense, and they may just be errors as Michael Hanson has mentioned.

To answer Ronald -- L36 with 3.70 takes the '853' tag; the reason the UPC M20/21/22 table shows '855' is because the power train chart shows 3.36 axle as the 'General Purpose' (standard) ratio for the close ratio 4-speed trans. The 3.70 is the 'Mountain' ratio for the 390hp with the close ratio trans. Likewise for the L72; standard axle was 3.55, with 3.36 also available under the '855' trans tag, and 3.70 and 4.11 available with the '853' trans. In 1966 you needed to order the L88 to get a 4.56 axle from the factory.

Wayne-----


As I recall, in previous discussions regarding transmissions some apparently original metal part number tags were found on cars that did not match any of the part numbers shown in the AIM or otherwise. These numbers were all very close to the numbers that are shown in the AIM leading one to believe they were part of the same "series" of transmission part numbers originally installed in the cars.

[Ronald L.]

Re: 66 Muncie differences 3880853/3880855

I went back and read under 4 different threads what you guys were writing 3 to 7 years ago...

Can't say that any sheds more light on the situation than this thread. Joe - do you have the powertrain chart that would put this all on paper?

[Wayne M.]

Re: 66 Muncie differences 3880853/3880855

. ..... - do you have the powertrain chart that would put this all on paper?

Ronald -- P.T. chart is found in the NCRS pocket guide (Corvette Specifications Guide, Volume One, by John Amgwert). Maybe the company store has it.

[Michael H.]

Re: 66 Muncie differences 3880853/3880855

I went back and read under 4 different threads what you guys were writing 3 to 7 years ago...

Can't say that any sheds more light on the situation than this thread. Joe - do you have the powertrain chart that would put this all on paper?

Look in your 66 AIM in the optional 4-speed transmission section M20/M21. Compare that information to that found on the G81 positraction differential section. The numbers for the M21/3.70 do not agree.

On the G81 page, the transmission shown for 3.70/4.11 is a 3880853 to be used with L36/L72. No mention of L79.

On the M21 page, the same 3880853 with 3.70/4.11 is shown as used with L79 only.
There is a different part number, 3880855, for L36/L72 with 3.70/4.11. That makes no sense. Should be the exact same transmission used with L79 with 3.70/4.11.

If I remember correctly, there are more errors on the AIM sheets and also some errors on the AMA spec sheets.

A 1966 printing of the parts book also calls for the 3880853 for L36/L72 with 3.70/4.11.

[Michael H.]

Re: 66 Muncie differences 3880853/3880855

- do you have the powertrain chart that would put this all on paper?

Here are the M21 and G81 AIM charts.

[Ronald L.]

Re: 66 Muncie differences 3880853/3880855

These are the pages I reference above instead of posting a JPG with the scanner broken right now, I was looking for more of a sales option chart from the day that would show what came with what.

That would be neat to have a part book from 66 too!

[Jack P.]

Re: 66 Muncie differences 3880853/3880855

These are the pages I reference above instead of posting a JPG with the scanner broken right now, I was looking for more of a sales option chart from the day that would show what came with what.

That would be neat to have a part book from 66 too!

Hope this helps, from 53-69 GM parts book






Jack

[John H.]

Re: 66 Muncie differences 3880853/3880855

I was looking for more of a sales option chart from the day that would show what came with what.

The 1953-1967 NCRS Pocket Spec Guide has the '66 Powertrain Chart that shows all the available engine/transmission/axle ratio combinations.

[Ronald L.]

Re: 66 Muncie differences 3880853/3880855

I found that simple chart at corvette.net, great reference.

[John R.]

Re: 66 Muncie differences 3880853/3880855

Ron, was just reading this post. I have a very original L36 with AZ code rear, 3.55, and a 3880853 tranny tag(orig). 82k mile car.