What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Manual Tranny Differences

2High4U

2High4U

1/2 ton status
Joined
Aug 20, 2005
Posts
542
Reaction score
0
Location
Felton Pennsylvania
I was wondering what the difference was from a sm465 and a m20 does anyone know?

sm - saginaw
m - muncie

is the difference just gear ratios cause iirc they look identicle
 
Apparently M20 is just a generic 4 speed manual trans RPO designation, like G80 could be posi, gov-lock, etc.

The M20 in cars is a wide ratio 4 speed (Camaro's, firebirds, etc) and was the companion to the M21/22 trannies. M20 in the trucks IS the 465, although I believe "SM465" is a misnomer. You won't see that in any GM literature. "C465" is what I believe to be correct, to be picky.
 
M20s, M21s, and M22s are passenger car trannys.

you may be getting the "M20" mixed up with the SM420, which looks very similar to an SM465 IIRC. the SM420 was the standard trans before the SM465.

and i believe the "SM" stands for Saginaw Muncie. i could be wrong there though.
 
The reason that i was wondering is because my grandfather has a 87 chevy dumptruck and it has a M20 in it. I thought that since it was a dump truck the tranny would be a more heavy duty manual.
 
beater_k20 said:
M20s, M21s, and M22s are passenger car trannys.

you may be getting the "M20" mixed up with the SM420, which looks very similar to an SM465 IIRC. the SM420 was the standard trans before the SM465.
Click to expand...

No, the problem is that M20, M21 and M22 are all RPO's, not tranny names. You could have the M20 RPO in a Camaro or a truck. Neither of which would be the same transmission. M20 even in Camaro's only designated 4 speed manual, you could get a Saginaw or Muncie trans with that RPO, it depended on the engine to which the car got.

465 is the actual transmission designation, like 700-R4.
 
actually, we're both incorrect, to a point.

M20s, M21s, and M22s are Muncie model numbers for different transmissions.

Muncie 4-speeds were produced in two different ratios wide ratio (M-20) and close-ratio (M-21). An extra heavy duty close-ratio version (M-22) was also offered on many of the big-block high-performance models.
Click to expand...
http://www.yearone.com/updatedsinglepages/Id_info/muncie.asp

however, option code M20 is for a 117mm 6.55 1st gear 4 speed... sounds like a 465 to me.
 
beater_k20 said:
actually, we're both incorrect, to a point.

M20s, M21s, and M22s are Muncie model numbers for different transmissions.

http://www.yearone.com/updatedsinglepages/Id_info/muncie.asp

however, option code M20 is for a 117mm 6.55 1st gear 4 speed... sounds like a 465 to me.
Click to expand...


Not to drag this out, but I will anyways. :)

I don't see anywhere that says *Muncie* gave it's transmissions the M20 designation.

You do however, see that GM called the 465 a 465, but the *RPO* is still M20. 350, 400, 700R4 all use an RPO code that has no basis in what Hydra-matic called them.

M20 could be had in a car, it could be in a truck. M20 in a '73-91 truck is nothing like the M20 in a 1968 Camaro, whether it be a Saginaw or a Muncie.

While a Muncie M20 may be well known in common automotive vernacular, it's usage has no technical basis. If I started saying my truck had an M20 (which is the correct RPO) people would ask how or why I put a car trans in there. :)
 
I'm not sure where I picked uit up... I'm quite certain the 'SM' designation refers to "Syncro-Mesh".
 
Maybe only GM knows for sure??

Many of my parts catalogs for bearings and seals,and one of my older GM parts books refers to what we call an "SM465",...as something else!

According to them,it is in reality,a "CH465"!!..
They also mention a "M420" "Muncie" 4 spd (in the truck book)...

...and also a NP435 "Close Ratio" New Process 4 spd ..only seen one of those mated to a 4x4 T-case..saw one in an 82 K10 with a 6.2!-and it was an OVERDRIVE!:eek1:

Another baffling listing under 1/2-1 ton 4wd trucks is a "Clark 5 Spd" !!!!!
I've yet to see one mated to ANY transfer case yet!--but have seen plenty of them in C60-C80 series School Busses and dump trucks.....

Anyone else ever seen one??..closest I came was a friends 1961 C20 Suburban Carryall..it had a 235 -6 with a factory Clark 5 spd tranny!..also had torsion bar front suspension(2wd!)..its THE only "light" truck I've ever seen with one from the factory...:eek1:

I have no clue if "CH" means "Chevrolet"??. so would a GMC have a "GM465"??

At any rate,I doubt "SM" means "Synchro-Mesh"..seeing fisrt gear has straight cut non syncro gears,as already mentioned by Atho..

Ahh..the wonderful world of confusing parts book listings.:what: :screwy: :dunno: :surepal:
...its a miracle anyone gets the right part even 20% of the time..:p: ..
 
Hmm a friends of mine has a 76 c60 its a huge stake body looks almost like a tractor trailer with the 20 inch spoke rims and two speed rear he was going to sell it to me for 500 but I didnt have room for something that huge.

Anyways to get to the point it had what i thought was a sm465 im not really sure to this day what is in it but it had the same gear pattern and stuff along with a button to change the gear ratio in the rear end.

never seen anything like that before changing the gear in the rear by pushing a button!:eek1:
 
yup --2 speed rear ends!..

Many of the larger 1-1/2-2 ton trucks and Busses had those 2 speed rear axles..a small electric motor with a worm gear (almost identical to a power window motor) was used to "shift" them!..the shift button was mounted on the shifter just under the shift knob,or stuck out of its center!..one of the ramp trucks we had at the junkyard had that in it..(an older "cab over" Ford F-8000 series..looked like an old home heating oil delivery truck cab)...


Now if GM (or any other manufacturer) had the insight to produce a FRONT axle with the 2 speed setup just like the rears,and put them in a 4x4,wouldn't THAT be the berries??--sorta like a "Dana 90" instead of a D60!--with 2 speeds!:D ...

A "K60" 4x4 !!.:bow: .with the 427 "tall deck" BB motor,and a Clark 5 speed!..or maybe even a "brownie" auxillary tranny behind the Clark!--I've seen C-60's with a 3 or 4 speed BEHIND the "main" tranny (Usually a Clark 5 spd!)..

Bet THAT would do some crawlin and pulling..I think the 2 speed rears had like 7.17's in the "low" ratio!...:eek1: --the "high" range was mostly so you could go 60mph or so, without the motor going 8 grand...:crazy:
 
yeah having a 2 speed front and rear axle would deff be cool they would have to switch at the same time tho or kaboom
 
diesel4me said:
...and also a NP435 "Close Ratio" New Process 4 spd ..only seen one of those mated to a 4x4 T-case..saw one in an 82 K10 with a 6.2!-and it was an OVERDRIVE!
Click to expand...

Its an NP trans, but not a 435... its the rpo MY6 or 89mm side-loader 3-spd + OD trans. Better known as an A833 or NP440 in the Dodge world.


Another baffling listing under 1/2-1 ton 4wd trucks is a "Clark 5 Spd" !!!!! I've yet to see one mated to ANY transfer case yet... closest I came was a friends 1961 C20 Suburban Carryall..it had a 235 -6 with a factory Clark 5 spd tranny!....its THE only "light" truck I've ever seen with one from the factory...
Click to expand...

IH offered a 5-speed in their light trucks also. Mind you, most were direct-5th, and 4x4s of that era would have used a divorce case - GM thru '66, and IH right through to '75 I believe.

At any rate,I doubt "SM" means "Synchro-Mesh"..
Click to expand...

I'm just throwing it out there as a possibility :o. There was the SM318/SM326/SM330 3-spds in addition to the 420.

Supposing 'Saginaw-Muncie' is correct... does that imply the such a model of trans could have been produced at either plant? And suggests the M20/21/22 were built exclusively at the Muncie plant?

Perhaps the 'CH' means 'Cleveland-Hydramatic'? It does seem odd for a manual trans to be produced in an engine assembly or auto transmission plant. Hmmm.... :thinking:
 
You must log in or register to reply here.

Latest Posts

Top Bottom