Just picked up this 1978, 4sp, radio delete, 305 2bbl

[O. D. Showtime]

Welcome to the site! Good looking wagon!

 

[pagrunt]

M20 was used for all GM made wide ratio 4 speeds since the intro of the Muncie & the Saginaw. M21 was close ration, M22 was close ratio-heavy duty, Muncie only. Not sure of the early '60's T10, but late '70's T10 was M24. They were the close ratio replacement of the M21, M20 then was the Saginaw. MM4 was a merchandising RPO for all manual 4 speeds.

 

[Ribbedroof]

yes and no, it is an rpo code, which gm used to specify a particular component based on the car and year. for example, an lt1 eng in 71 is not the same as in 93 or in 2018.

My point exactly, the RPO code has nothing to do with the actual hard part over the long haul, but by nature of the parts used during that time frame does specify a particular unit. Before Muncies, they were T10s, and after Muncies they were Saginaws (M20) or B/W Super T10s (M21)...both designators also used for Muncies. People just got accustomed to referring to stuff by the RPO during the muscle era.

that may be correct for a g body. but his is an A body. in my 79 service manual, the 4speed manual is listed as the m-20 option.
joe

GM's sales/ordering documents used MM4 for the 1979 model year onward...service manuals are often "retreads" of the previous year's manual, with additions for newly-introduced components.

The whole A body G body designation change was not very well thought out, but I don't think GM really was concerned with what would happen in the future.

So concludes my 2 cent's worth 🙂

I'm a slow typer, you beat me

 

[grandamman]

Does it have a factory tach?
Did the Chevy factory 4 speed come with a 2 barrel?

 

[MrSony]

Awesome.

 

[abadwillys]

Nice wagon, the 4 speed is cool
I dont think its a factory 4 speed, could have been a 3 speed tho
the factory mounted a sheet metal "hump" towards the left side of the tunnel providing shifter clearance, it will be spot welded/seam sealed to the floor, you can either check it from underneath or take out a sill plate, lift the carpet up and feel in there with your hand.

fwiw my wagon was a factory 3 speed, i have long since removed the "hump" and sheet metal'd it over, but my clutch pedal is still in the car

 

[Texas82GP]

Welcome to the site from Houston. That's a cool car. It presents well in the pictures. I'll bet it's fun to drive. Enjoy!

 

[aj1434]

Does it have a factory tach?
Did the Chevy factory 4 speed come with a 2 barrel?

Yes, mine has a factory Tach and has a 2bbl, really a weird car, bare bones other than for some reason It has factory air. Its radio delete crank windows, hell the back door windows dont even open or even have cranks.

 

[aj1434]

Welcome to the site from Houston. That's a cool car. It presents well in the pictures. I'll bet it's fun to drive. Enjoy!

Thanks for the compliment, It is fun to drive, It does show well but I do have to replace the rusted out hood and was thinking of putting a steel cowl hood on. Gotta fix a little area on the tailgate where there is a dent. The rest of the body seems rust free.

 

[aj1434]

Nice wagon, the 4 speed is cool
I dont think its a factory 4 speed, could have been a 3 speed tho
the factory mounted a sheet metal "hump" towards the left side of the tunnel providing shifter clearance, it will be spot welded/seam sealed to the floor, you can either check it from underneath or take out a sill plate, lift the carpet up and feel in there with your hand.

fwiw my wagon was a factory 3 speed, i have long since removed the "hump" and sheet metal'd it over, but my clutch pedal is still in the car

I am hoping it is a factory 4 speed, from what I know, they did make some and I hope mine is one of them. Just hard to verify without a build sheet.