Factory Manual Overdrive Transmission - What can you tell me about it?

[70chevroletCST]

Hey you! Yeah, you! I'm talking to the 67-72 Chevy expert. I've just discovered an interesting option that I'd never heard about. Factory manual 3-speed with Overdrive. Option M10. I did search for old posts but only found a little information. So really what I'm looking for is just whatever you can tell about it. How many years it was offered? What engines could be combined with it? How many trucks were produced with it?? Anything else?

This truck came across Facebook Marketplace a couple days, lasting only 4 hours before sold.. If only I had caught it sooner. I would've LOVED to have it. The best deals always go fast. Take a close look at that SPID. My interest wasn't contained to just the overdrive. Factory tachometer, paint stripe instead of upper trim, and positraction rear end. Certainly looks to have been special ordered rather than a standard dealership lot model.

Thanks in advance to anyone who replies!
Thanks to the Admins for keeping this great forum site alive!

1969 Chevrolet CST/10 Short bed

[1970cstblazer]

That is an oddly optioned truck for sure. That would have been a great one to scoop up. Original paint too..

https://67-72chevytrucks.com/vboard/...&highlight=m10

https://67-72chevytrucks.com/vboard/...ight=overdrive

https://67-72chevytrucks.com/vboard/...d.php?t=562546

https://67-72chevytrucks.com/vboard/...ight=overdrive

[Accelo]

4:11 times the over drive ratio is a 2.87 equivalent differential ratio.
I have driven them and they are nice.

Kind of like driving a power-glide transmission on the highway.
You floor the throttle and it kicks down to direct drive and when you let up it shift back into OD.
The bad news is there is no compression braking while in OD. The vehicle just over-runs. GM did this to keep the cost down.
Also notice the system grounds out the ignition (points) for part of a second to keep the over-drive from shifting under load.
Cheers

[dagnabbitt]

There's one in my town, it is also a 1969 three on the tree. Very cool indeed.

[70chevroletCST]

Thank you all for the replies and information. The shared links too!

Seems like a pretty neat system. Maybe I'll get a chance to try one out myself someday.

[71 super]

I bought this truck. It is an interesting truck for sure, cranks right up and things work as they should. It needs a lot of work, but it is going to be a cool truck when restored back. The only thing missing is the brackets for the power steering pump, everything else is there.

[70chevroletCST]

Originally Posted by 71 super

I bought this truck. It is an interesting truck for sure, cranks right up and things work as they should. It needs a lot of work, but it is going to be a cool truck when restored back. The only thing missing is the brackets for the power steering pump, everything else is there.

That's awesome! I didn't even think about the new owner coming across this post.
What are your plans for the truck? Also, did it come with the doors it was missing in the pics?

[71 super]

Yes it has both doors, the passenger side is pretty bad. Currently my plans are on hold as I had knee replacement yesterday, however it will be a stock restore that will likely be my sons first truck.I would much rather start him with a 250 than 396/402. We will see how he does over next three years.

[70chevroletCST]

Wow, you got a complete truck for a great price then! (Even if it needs some rust work etc.) I think that truck is a prime candidate for factory stock type of restoration. It is different enough where it would stand out more like it is rather than if you slap a 350 and an auto trans in it. Very neat factory combination. Hope to see you post some progress pics as you go along.

If for some reason you find this project needing to find a new home, please reach out to me. I'd be very grateful to have first crack at taking it off your hands. (I can PM you my name and number if needed)

Hoping for a quick recovery for your knee surgery! A couple family members of mine had replacements this year. Tough road for a while, but seems to be well worth it in the end.

[Palf70Step]

from what I emember th overdrive ones are not synchronized gears other than that, it is a good unit.

[RichardJ]

The '67 and earlier 3 spd with 4 bolt side cover has a non-syncro 1st gear. The '68 and newer Sag 3 spd with 7 bolt cover is synchronized. The Sag 3 spd and the sag 4 spd are very similar and the overdrive from the 3 spd Sag will bolt to the sag 4 spd with little to no modifications.

I've never done it, but have read about it on this forum several times.

The second link, 70tsblazer posted above mentioned the 4 spd + overdrive.
https://67-72chevytrucks.com/vboard/...ight=overdrive

frankslagoon even posted this picture. of one he built.

Years ago I replaced my '67 3 spd with a SM465. The car 4 spd Sag trans are not hard to find, but the late overdrive unit are nearly non-existent.

[Already Gone]

Bought this one with 307 and O/D about 10 years ago and flipped it pretty quick, but kicking my ass now.

[MikeB]

Originally Posted by Already Gone

Bought this one with 307 and O/D about 10 years ago and flipped it pretty quick, but kicking my ass now.

V-8 and manual trans. That's very cool!

My 69 was 307 and TH350, but with no A/C, power steering, or power brakes.

[70chevroletCST]

Originally Posted by Already Gone

Bought this one with 307 and O/D about 10 years ago and flipped it pretty quick, but kicking my ass now.

Awesome, I think I had read somewhere it could come with the small V8 option, and this is the proof. Looks like that was one heck of a truck overall. I think we all have stories of trucks that should've been kept around. Especially now since the market for these has jumped!

[70chevroletCST]

Originally Posted by RichardJ

The '67 and earlier 3 spd with 4 bolt side cover has a non-syncro 1st gear. The '68 and newer Sag 3 spd with 7 bolt cover is synchronized. The Sag 3 spd and the sag 4 spd are very similar and the overdrive from the 3 spd Sag will bolt to the sag 4 spd with little to no modifications.

Thank you for the information!

[1970cstblazer]

Wow, Black on red/307/3ott/OD/CST/Tach/Speedminder!
Darn rare combo!

[Palf70Step]

i guess I am confused a litle . The OD one I had was not an add on, it was a 3-spd OD tranny. I didn't realize there was a style the could be added on from the factory.

[RichardJ]

>>it was a 3-spd OD tranny.<< ??

Do you mean a 3 spd + OD or are you thinking of a 4 spd with a 4th od ratio.
Mopar converted their A833 4 spd to a overdrive trans by switching 3rd and 4th gears. Direct drive through the trans was selected as 3rd. The original 3rd gears were cut as overdrive instead of underdrive and was selected as 4th gear.
Dodge used this OD A833 in their cars and trucks starting in 1975 and Chevy trucks used it '80-'86.

[MikeB]

Originally Posted by RichardJ

Mopar converted their A833 4 spd to a overdrive trans by switching 3rd and 4th gears.

I have a buddy with that 4-speed OD trans in a 73 Cuda that came from the factory with a 3-speed. He had a few problems initially, but got help and parts from a company on the east coast that specialized in Mopar transmissions.
There used to be a company that did the same thing with Muncie 4-speeds, but I can't remember their name.

I do know that AutoGear sells a "ultra-wide ratio" Muncie replacement trans (or just the gear set) with a 2.98 1st gear that allows you to run a 3.23 or 3.08 axle w/o a lot of clutch slipping in 1st. Ratios are 2.98/2.04/1.46/1.00. Even a 2.73 axle should work in a light vehicle with 26"-27" tires.

[Palf70Step]

Originally Posted by RichardJ

>>it was a 3-spd OD tranny.<< ??

Do you mean a 3 spd + OD or are you thinking of a 4 spd with a 4th od ratio.
Mopar converted their A833 4 spd to a overdrive trans by switching 3rd and 4th gears. Direct drive through the trans was selected as 3rd. The original 3rd gears were cut as overdrive instead of underdrive and was selected as 4th gear.
Dodge used this OD A833 in their cars and trucks starting in 1975 and Chevy trucks used it '80-'86.

No it wasn't that one. I knew about them in square body trucks. I remember one in ihe late 50s cars that was a normal 3 speed with a cable pull to engage the OD. I had a 69 that had something that seemed to be same. It was not a saginaw with an addon OD. it was all in one. And non synchtro gears. Some one before my uncle may have taken an older tranny aNd put it place if the normal 3 speed. It was in a 250 6 truck

[Keith Seymore]

Originally Posted by richardj

dodge used this od a833 in their cars and trucks starting in 1975 and chevy trucks used it '80-'86.

- '87.



k

[Accelo]

One can find the transmissions but the rest of the parts are difficult.
I did save this from years ago. Maybe it will help someone with the wiring someday?

[pjmoreland]

I used to have a '67 shortbed C10 that I bought from the original owner who ordered it from the factory that way. It had a 250 I6 engine, a three-on-the-tree manual transmission, 4.11 rear end with posi, a one-piece driveshaft and an overdrive unit that was attached to the tail of the transmission. He had removed the stock throttle-mounted shift solenoid switch, and had replaced with a toggle switch on the dash. There was a mechanical cable tee handle on the lower edge of the dash labeled OVERDRIVE that had to be pushed in. This would put the transmission in a freewheeling mode where the engine could idle down while coasting down the road in gear. To engage the overdrive, I'd rev the engine up, flip the toggle switch, let off the gas, and as the engine started idling down, there would be a satisfying clunk as the overdrive engaged as the correct RPM was reached. I'd have to remember to disengage overdrive before coming to a stop, or else I'd have a really tall first gear plus overdrive when starting up again.

[MikeB]

Had a buddy way back in the day with a 57 Ford with a 312, 3 speed manual, and OD. I still remember flying down the highway with OD engaged and the engine turning just a few hundred RPM above idle. Letting off the gas pedal would then cause the engine to fall back to idle speed. It was a strange sensation for me, a guy with a 57 Chevy with conventional 3-speed trans, and a 283 wailing at 70mph.

Many years later my family truckster was a Volvo station wagon with 4-speed manual and OD. That one had thumb switch on the gearshift knob that I would click to the OD-ON position. I'd then let off the gas pedal and push in the clutch pedal half-way, which would engage the OD.

I found out recently that the Volvo OD unit was made by a company called GKN. Turns out the modern Gear Vendor units are produced under a license from GKN. Small world!

[BanjoDude]

Originally Posted by MikeB

Had a buddy way back in the day with a 57 Ford with a 312, 3 speed manual, and OD. I still remember flying down the highway with OD engaged and the engine turning just a few hundred RPM above idle. Letting off the gas pedal would then cause the engine to fall back to idle speed. It was a strange sensation for me, a guy with a 57 Chevy with conventional 3-speed trans, and a 283 wailing at 70mph.

Many years later my family truckster was a Volvo station wagon with 4-speed manual and OD. That one had thumb switch on the gearshift knob that I would click to the OD-ON position. I'd then let off the gas pedal and push in the clutch pedal half-way, which would engage the OD.

I found out recently that the Volvo OD unit was made by a company called GKN. Turns out the modern Gear Vendor units are produced under a license from GKN. Small world!

That's really interesting. I'm restoring a 73 Triumph GT6 that has a Laycock overdrive which can be engaged in both 3rd and 4th gear. It has that identical switch.