Original 1967 M21 Muncie restoration
I.m offering these photos for information purposes. I would love hearing any commentary for judges, or those experienced with Muncie four speeds. All observations and thoughts appreciated.
I just got my M21 Muncie rebuilt from my 45,000 mile 1967 L68 400hp 427 barn-find. Fellow NCRS member and occasional visitor to this site Scott Pfuehler restored/rebuilt this Muncie for me.
Scott has been rebuilding these for longer than he can probably remember, so I take his internal evaluations and conclusions as textbook. In Scott's opinion, even though my Corvette is about 98% original, my Muncie had been apart before at least once. It is definitely the original M21 four speed that came in my car (factory VIN stamped), but there is always the possibility that some bolts, etc. ....had been changed out at it's last servicing.
I am the fifth owner of this Corvette, but owner number four bought it somewhere around December 1973, or early 1974. He put in on blocks in his barn around 1977 or 1978. It sat in the barn until I purchased it in 2006.
I have tracked down owners number 3 and 2, but not the first owner. I do know that the first owner used the Corvette strictly for drag racing for an unknown period of time (my guess, two to five years, based on the low mileage on the car). When found, the Corvette was wearing vintage aluminum wheels, headers, the TI replaced with a dual point dist., and had been running seven inch slicks. The car was factory built with soft-top only, but an auxiliary hardtop was installed with the soft top frame removed. (For anyone who has never gone thru the traps at 120mph, a convertible top fluttering int he wind is a little un-nerving.) The car was ordered with a 4:11 positraction. It had a Hurst shifter installed.
The rebuild found that the internal parts were in overall excellent and unworn condition, except for synchronizers and 3rd and 4th gears showing chips on teeth (my guess, high RPM shifts halfway down the drag strip). My VIN: 140XX (assembled around March 18th,, 1967).
Main case casting number: 3885010 One ring in the input shaft (M21). The transmission still had the broadcast code tag attached to a side cover bolt. The casting number side of the main case has to cast in codes (molds perhaps) R-1, and 7-1. The Muncie assembly code is P7C07, with an additional partial "7" after the last seven (bounce perhaps). The VIN stamping is correct, and begins with "7S".
The tail housing is casting number 3857584, with the characteristic double circles with a line thru them. One circle has a "C M" in the upper part, and a "2 2" in the lower. The second circle (status?) has two dots in the top, and a "2" below. The top three tail hosuing bolts are marked "S B C". and then two lower with "G", and one with the three outward lines (grade three).
The side cover is casting 3884685, and has seven bolts marked "S B C". The side cover has the same two characteristic circles with a line thru them. One has a "C M" on the top, and a "4-1" below. The second has two dots on the top, and a "1 1" below.
The drain plug has either a "M", or a "W" with a line below.
The restored appearance of the aluminum castings is due to my having them re-skinned (yes, I know this term isn';t correct, but the use of the term helps in understanding the issue, in my opinion).
The aluminum castings were in superb condition (no real denting, or scratches as you can see), but heavy staining from grease leakage sitting on them for 43 years or so.
All bolts were natural. They were wire brushed and lightly coated with oil. All threads were fortunately, in perfect condition.
Once again, comments including critical commentary is welcome and appreciated. Sorry if too long winded in my description. Ridge.
I just got my M21 Muncie rebuilt from my 45,000 mile 1967 L68 400hp 427 barn-find. Fellow NCRS member and occasional visitor to this site Scott Pfuehler restored/rebuilt this Muncie for me.
Scott has been rebuilding these for longer than he can probably remember, so I take his internal evaluations and conclusions as textbook. In Scott's opinion, even though my Corvette is about 98% original, my Muncie had been apart before at least once. It is definitely the original M21 four speed that came in my car (factory VIN stamped), but there is always the possibility that some bolts, etc. ....had been changed out at it's last servicing.
I am the fifth owner of this Corvette, but owner number four bought it somewhere around December 1973, or early 1974. He put in on blocks in his barn around 1977 or 1978. It sat in the barn until I purchased it in 2006.
I have tracked down owners number 3 and 2, but not the first owner. I do know that the first owner used the Corvette strictly for drag racing for an unknown period of time (my guess, two to five years, based on the low mileage on the car). When found, the Corvette was wearing vintage aluminum wheels, headers, the TI replaced with a dual point dist., and had been running seven inch slicks. The car was factory built with soft-top only, but an auxiliary hardtop was installed with the soft top frame removed. (For anyone who has never gone thru the traps at 120mph, a convertible top fluttering int he wind is a little un-nerving.) The car was ordered with a 4:11 positraction. It had a Hurst shifter installed.
The rebuild found that the internal parts were in overall excellent and unworn condition, except for synchronizers and 3rd and 4th gears showing chips on teeth (my guess, high RPM shifts halfway down the drag strip). My VIN: 140XX (assembled around March 18th,, 1967).
Main case casting number: 3885010 One ring in the input shaft (M21). The transmission still had the broadcast code tag attached to a side cover bolt. The casting number side of the main case has to cast in codes (molds perhaps) R-1, and 7-1. The Muncie assembly code is P7C07, with an additional partial "7" after the last seven (bounce perhaps). The VIN stamping is correct, and begins with "7S".
The tail housing is casting number 3857584, with the characteristic double circles with a line thru them. One circle has a "C M" in the upper part, and a "2 2" in the lower. The second circle (status?) has two dots in the top, and a "2" below. The top three tail hosuing bolts are marked "S B C". and then two lower with "G", and one with the three outward lines (grade three).
The side cover is casting 3884685, and has seven bolts marked "S B C". The side cover has the same two characteristic circles with a line thru them. One has a "C M" on the top, and a "4-1" below. The second has two dots on the top, and a "1 1" below.
The drain plug has either a "M", or a "W" with a line below.
The restored appearance of the aluminum castings is due to my having them re-skinned (yes, I know this term isn';t correct, but the use of the term helps in understanding the issue, in my opinion).
The aluminum castings were in superb condition (no real denting, or scratches as you can see), but heavy staining from grease leakage sitting on them for 43 years or so.
All bolts were natural. They were wire brushed and lightly coated with oil. All threads were fortunately, in perfect condition.
Once again, comments including critical commentary is welcome and appreciated. Sorry if too long winded in my description. Ridge.
. My thoughts on what you've speculated as a "bounce" in the assembly date code. I've seen this before, 3 variations so far, all in the '66-7 "010" case era. Thumbnail pic below is another mark, and I've seen a 3-sided square (half height) that leads some eBay sellers to interpret as a "C" and claim M22 
. IMO, it's an identifier, either for the shift or the assembler himself. This one's on a 1966 tranny.
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