M20 Need Clarification - Chevelle Tech
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post #1 of 15 (permalink) Old Apr 30th, 10, 2:21 PM Thread Starter
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M20 Need Clarification

Hi Guys,

I have a M20

ID: P9C04A (Muncie - 1969 - March - 4th - M20)

Vin: 19B366327 ?

Main Body # 3925660 1968 - 1970

Tailhouse # 384629 ?

Input Shaft: 10 Tooth and 2 Rings

Output Shaft: 27 Tooth

When I look at "Identifying Muncie 4 Speeds II" info, I don't see "10 Tooth and 2 rings" for the input shaft and "27 Tooth output shaft" combined together under "Input Shaft Tooth and Spline Count Related to Year" section. What am I missing here? I've counted the output shaft 3 or 4 times and I come up with 27 Tooth. Am I interpreting the ID info incorectly? Is the Tooth count different than Spline Count? I have this trany on a work bench so it's easy to see all identifying info and get the tooth count.

Any additional help with ID, Vin or what vehicle you may think this came out of originally would also be great. It was in my 69' when I got it but the VIN on the trans does not match my VIN.

Thanks for any help.

Brian


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post #2 of 15 (permalink) Old Apr 30th, 10, 2:51 PM
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Re: M20 Need Clarification

Quote:
Originally Posted by fastss396man View Post
Hi Guys,

I have a M20

ID: P9C04A (Muncie - 1969 - March - 4th - M20)

Vin: 19B366327 ?

Main Body # 3925660 1968 - 1970

Tailhouse # 384629 ?

Input Shaft: 10 Tooth and 2 Rings

Output Shaft: 27 Tooth

When I look at "Identifying Muncie 4 Speeds II" info, I don't see "10 Tooth and 2 rings" for the input shaft and "27 Tooth output shaft" combined together under "Input Shaft Tooth and Spline Count Related to Year" section. What am I missing here? I've counted the output shaft 3 or 4 times and I come up with 27 Tooth. Am I interpreting the ID info incorectly? Is the Tooth count different than Spline Count? I have this trany on a work bench so it's easy to see all identifying info and get the tooth count.

Any additional help with ID, Vin or what vehicle you may think this came out of originally would also be great. It was in my 69' when I got it but the VIN on the trans does not match my VIN.

Thanks for any help.

Brian
Brian. Don't know what site you're looking at "Identifying Muncie 4 Speeds II" but I show the 66-70 M20 with a 10-spline (not 10-tooth) and 2-ring input shaft - http://chevellestuff.com/qd/muncie.htm. The 10-spline unit should have a 21-tooth count.


This photo is to show the M20/M21 vs M22 gear cut angle but these are the 'tooth count' referred to.


The input shaft spline.

Transmission appears to have been installed on a 1969 (9) Baltimore-built (B) Chevelle (sequence starting with 300001) and 366327 is late March - last GM reported sequence for March at Baltimore was 367113.

TC Gold #92 ~ August 1998
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post #3 of 15 (permalink) Old Apr 30th, 10, 3:24 PM Thread Starter
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Re: M20 Need Clarification

Dale,

Thanks for the link. The info I had on file was from May of 03'. Must have been some bad info. Reading the info available at the link you supplied clarified my concerns.

Have a great weekend.

Brian


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post #4 of 15 (permalink) Old Apr 30th, 10, 6:53 PM
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Re: M20 Need Clarification

That link has some mis-information also... Crash
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post #5 of 15 (permalink) Old Apr 30th, 10, 7:00 PM
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Re: M20 Need Clarification

Quote:
Originally Posted by crashent View Post
That link has some mis-information also... Crash
Would you kindly tell us what is incorrect in the link Dale provided?

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post #6 of 15 (permalink) Old Apr 30th, 10, 10:25 PM
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Re: M20 Need Clarification

Quote:
Originally Posted by crashent View Post
That link has some mis-information also... Crash
Yes, I'd be interested to know as well. I care more about being right. Either email or PM me with specifics if you will. Thanks!

TC Gold #92 ~ August 1998
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post #7 of 15 (permalink) Old May 1st, 10, 11:32 AM
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Re: M20 Need Clarification

From the top of the page...

3885010 casting was used 1966-67 NOT 1965-67

M-22 production started in 1965 NOT 1967
1965-1970 M-22 used 10 spline inputs
1970 LS-6 and 1971-74 M-22 used 26 spline inputs

CASTING NUMBERS

3839606 main case was NOT used in 1963...
Early 1964 only

3846429 thin rib tail housing was NOT used in 1963...
Early 1964 only

9779246 tail housing was used 1964-68 in Pontiacs & Olds

3846429 regular rib tail housing was used 1964 thru the end of the 1970 model year...

All the dates are model year, because Muncie are date as model year, NOT calender year like blocks, heads, exhaust manifolds, ect...

This same mis-information is on almost every Muncie web page I've seen, which leads me to believe a lot of people cut and paste without checking the accuracy of the information...

Hope this helps... Crash
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post #8 of 15 (permalink) Old May 1st, 10, 1:08 PM
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Re: M20 Need Clarification

M22 production did indeed begin in 1965, my error and I should have known better since the M22 as offered in 1966 Chevelles.

I did get most of this information from these two pages, http://www.5speeds.com/muncie2.htm and http://www.5speeds.com/casting.html so if they're wrong then I'm wrong but I'm certainly willing to make corrections.

As some of your information seems to be in conflict with them (and all I wish to know is what's correct, not who's correct), please excuse me if I ask a few questions.

Since the M22 was introduced in 1965, what main case casting was used for 1965 since you indicate 3885010 was used in 1966-67 only?

Approximately when in 1970 did the 10 spline input get replaced with the 26 spline input since both are stated for 1970? Or was the 10 spline input used with all non-LS6 1970 Chevelles and the 26 spline used only with LS6 1970 Chevelles?

What main case casting and tail housing casting was used in 1963 if not 3846429?

I think the date issue is described correctly in the paragraph
Quote:
In 1967 and 1968, the date code got a year designator and a letter designator for the month such as P8A01, meaning 1968 (8), January (A) 1st (01). Note that a Muncie dated with a September to December build date was actually built the prior calendar year. An example would be the date code P8T13, meaning 1968 (8), December (T), 13th. The transmission was assembled December 13, 1967 for the 1968 model year.
This is meant to explain the year designation in a date code is the model year, not the calendar year - emphasis added here for clarity.

Do you have a suggestion for a better way to describe it?

As always, input and corrections are welcomed. I'm not a Muncie guru or specialist by any means and (generally) take other sites at their word unless I know it from other research to be false. I doubt if there are any "official" GM or Muncie documents on things like casting numbers and data are arrived at through years of looking at original stuff and I trust experts in areas like this for correct information.

Appreciate the help!

TC Gold #92 ~ August 1998
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post #9 of 15 (permalink) Old May 1st, 10, 2:59 PM Thread Starter
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Re: M20 Need Clarification

Dale and Crash,

This (http://www.5speeds.com/muncie2.htm) web site is where I was getting my original info too, which was a bit confusing. Part of my problem was confusing the input and output shafts "visible" tooth count vs the spline count inside the trans not visible unless I open up the trans.

Thanks for the continued discussion to clarify any other discrepincies.

Brian


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post #10 of 15 (permalink) Old May 1st, 10, 3:53 PM
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Re: M20 Need Clarification

Dale, I think they still used the 3851325 case in 1965.

Here is some Muncie casting number information that I am almost positive is correct.
http://www.camaros.org/trans.shtml

Over the years I have seen a few 1970 Muncies with 26 spline inputs. I do remember that one was an M22 and one was an M21. But I can't say for sure if they were original or not. And I don't remember the partial VINs.

Colvin's books are good - but I have found minor discrepancies over the years. I can't say for sure if his Muncie information is all correct or not. But he also shows the 3851325 case in 1965.

Red 1967 Chevelle SS 396, 4 speed, 3.31 12 bolt posi, black bench seat interior, Bolero Red - long term restoration project
68 Camaro SS - 468 BBC, 781 heads, RPM Air Gap intake, Lakewood bellhousing, M21, BO coded 12 bolt - but 3.31 posi now. Old drag car, back on the street.

Last edited by bcmiller; May 1st, 10 at 6:28 PM.
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post #11 of 15 (permalink) Old May 1st, 10, 7:13 PM
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Re: M20 Need Clarification

Thanks, Byron. The 3851325 casting is shown for 63-65 for the M20 & M21 but for the M22 the Camaro.org site shows "removed." And therein lies the question, what was the casting for a 65 M22 if the 66-67 were different? I realize the thread was started with M20 questions but it was pointed out the M22 data is incorrect and that's what I'm trying to verify.

Camaros.org also notes the 70 M22 with casting 3925661 was used with a 10 spline input shaft and an asterisk note that, "Colvin reports that 454 Chevelle M22 in 1970 used the 1971-74 splines." Looking at Colvin's book, it states on page 237, "The second change was the addition of a fine-spline output shaft for Chevelle M22 applications. (All other transmission assemblies used a course [should be coarse] spline output shaft.) This dictated the use of a new extension housing, which was specific to the Chevelle M22 applications for the 1970 model year." The section goes on to say, "The 1971 model year marked the last of the major changes to the Muncie 4-speed. On all transmissions the input and output shafts were changed from coarse spline to fine spline."

Nothing is said about the input shaft being 10 or 26 spline in 1970, only the output shaft. In Camaro.org's defense I assume the M22 was a 454-only option so why bother to list it twice - once for 1970 with a 10 spline input shaft and a second time for 1971-1974 with a 26 spline input shaft and both with the same maincast number of 3925661?

In Colvin's table of the M22 (page 246) the maincase is still listed at #3925661 and the same main case for M20 & M21 as well on camaros.org.

TC Gold #92 ~ August 1998
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post #12 of 15 (permalink) Old May 1st, 10, 7:50 PM
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Re: M20 Need Clarification

Dale, since this was not directly related to the original post, I sent you a PM.

What CRG means by "removed" is better explained by Colvin. In 1965 the M22 case used was a 3851325 case machined out to use the 1 inch cluster pin. Then the casting number was ground off - or removed.

Bryon

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Last edited by bcmiller; May 1st, 10 at 8:28 PM.
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post #13 of 15 (permalink) Old May 1st, 10, 7:57 PM
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Re: M20 Need Clarification

No M22 in 67 Chevelles


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post #14 of 15 (permalink) Old May 1st, 10, 8:23 PM
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Re: M20 Need Clarification

Quote:
Originally Posted by 66 MYSTERY CHEVELLE View Post
No M22 in 67 Chevelles
I believe you are correct. Colvin says M22 used for Corvette only in 1967, with an unknown number produced. Part number on tag used is a rare one - 3879993.

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post #15 of 15 (permalink) Old May 1st, 10, 9:00 PM
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Re: M20 Need Clarification

Thanks for believing in me


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