72 Manual tranny question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gman · 09-02-2003, 11:32 PM

Help!

Got a couple questions that hopefully someone can help with. I have the original 4 spd manual tranny that my understanding is an SM465. What does the SM stand for? Also, someone told me that it is a Muncie 4 spd................as in a M20, M21 or M22. Is that correct? I don't think so. Which is it?........Any help appreciated.

1969 GMC · 09-02-2003, 11:50 PM

You're right, that tranny should be the SM465. The easiest way to tell is if it has reverse down to the passenger side. I am also curious to know what SM stands for.
On my option sheet, the RPO code for my transmission (SM465) is M20. I am confused by this, I thought the M20, 21, and 22 were car trannies. Maybe someone else can shed some light on this subject.

gman · 09-03-2003, 12:05 AM

yeah, its down and to the right. I believe my option sheet says that too but its not here with me to verify that.

**Yukon Jack** · 09-03-2003, 09:41 AM

Don't ask me why but most of us refer to that tranny as the SM465 when it is actually the CH465. I don't know what the CH stands for. It is listed in the Chevrolet Restoration packet as the Chevrolet CH465. I have never heard of the SM420 being called an CH420.

**kwmech** · 09-03-2003, 03:22 PM

I always thought it was saginaw muncie

jcueckert13 · 09-03-2003, 06:23 PM

the sm 420 was only used untill 1967 and it is a muncie

1969 GMC · 09-03-2003, 10:58 PM

i must disagree, the sm420 was used up until 1969. that is the year they switched to the sm465.

**'68OrangeSunshine** · 09-04-2003, 06:27 AM

SynchroMesh is what the SM stands for. The last year for U.S. production SM 420s was 1967. They continued making trucks with the 420 in Canada until they ran out. Muncie is a town in Indiana where they make transmissions for GM. Saginaw is a town in Michigan where GM also has a tranny plant. Both of these plants made more than one style of 4-speed and/or 3-speed, thus the confusion.I believe the RPO code on my '68 C/10's glovebox states "M20."
I used to think this was the famed "Muncie Rockcrusher," because I have gone out in the boonies and literally crushed rocks with it. I had a difference of opinion with some musclecar dude, who was sure the "Rockcrusher Muncie" was a car tranny so-called because it sounded like a box of rocks. I guess it all depends on if you're sitting around drinking beers with car guys or truckers.

09-02-2003, 11:32 PM	#1
gman Registered User Join Date: Nov 2000 Location: Ogden, Utah Posts: 290	72 Manual tranny question Help! Got a couple questions that hopefully someone can help with. I have the original 4 spd manual tranny that my understanding is an SM465. What does the SM stand for? Also, someone told me that it is a Muncie 4 spd................as in a M20, M21 or M22. Is that correct? I don't think so. Which is it?........Any help appreciated. __________________ 72 Chevy SWB Custom Deluxe K10, 350/SM465, PS, PB, Fact. Air 2000 Harley...Wide Glide

09-02-2003, 11:50 PM	#2
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	You're right, that tranny should be the SM465. The easiest way to tell is if it has reverse down to the passenger side. I am also curious to know what SM stands for. On my option sheet, the RPO code for my transmission (SM465) is M20. I am confused by this, I thought the M20, 21, and 22 were car trannies. Maybe someone else can shed some light on this subject. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

09-03-2003, 12:05 AM	#3
gman Registered User Join Date: Nov 2000 Location: Ogden, Utah Posts: 290	yeah, its down and to the right. I believe my option sheet says that too but its not here with me to verify that. __________________ 72 Chevy SWB Custom Deluxe K10, 350/SM465, PS, PB, Fact. Air 2000 Harley...Wide Glide

09-03-2003, 09:41 AM	#4
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,689	Don't ask me why but most of us refer to that tranny as the SM465 when it is actually the CH465. I don't know what the CH stands for. It is listed in the Chevrolet Restoration packet as the Chevrolet CH465. I have never heard of the SM420 being called an CH420. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

09-03-2003, 06:23 PM	#6
jcueckert13 Registered User Join Date: Apr 2003 Location: Edgewood New Mexico Posts: 2,088	the sm 420 was only used untill 1967 and it is a muncie __________________ 1990 subaru legcy (daily driver) 1987 Toyota 4runner (weekend toy) 1968 C30 flatbed dually 1970 C10 longbed stepside (in pieces) 1976 Dodge Dart 1963 Dodge Dart

09-03-2003, 03:22 PM	#5
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,717	I always thought it was saginaw muncie

09-03-2003, 10:58 PM	#7
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	i must disagree, the sm420 was used up until 1969. that is the year they switched to the sm465. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

09-04-2003, 06:27 AM	#8
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,622	SynchroMesh SynchroMesh is what the SM stands for. The last year for U.S. production SM 420s was 1967. They continued making trucks with the 420 in Canada until they ran out. Muncie is a town in Indiana where they make transmissions for GM. Saginaw is a town in Michigan where GM also has a tranny plant. Both of these plants made more than one style of 4-speed and/or 3-speed, thus the confusion.I believe the RPO code on my '68 C/10's glovebox states "M20." I used to think this was the famed "Muncie Rockcrusher," because I have gone out in the boonies and literally crushed rocks with it. I had a difference of opinion with some musclecar dude, who was sure the "Rockcrusher Muncie" was a car tranny so-called because it sounded like a box of rocks. I guess it all depends on if you're sitting around drinking beers with car guys or truckers. Last edited by '68OrangeSunshine; 09-04-2003 at 06:45 AM.



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