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identify 3 Speed Manual Transmission

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identify 3 Speed Manual Transmission

65C10Fleetside 65C10Fleetside
New User | Posts: 5 | Joined: 08/09
Posted: 08/25/09
07:04 PM

requesting info on my 3 Speed Trans. Column shifter installed in my 1965 C10 Fleetside with 292cid. here are numbers I think are correct. hard to read while installed. number on main unit: GM 21 3788188, number on tail: 3731811 or 3731911, number on 4 bolt side cover: GM 1181L8 or 11618L8. not sure if letter is L or not? side cover has 4 bolts, tail has 5 bolts. both shift levers on left side of unit, no levers on right. speedo cable connects on left of tail. i am also thinking about installing a different Trans, what would be an economical swap?  

chrischevy75 chrischevy75
New User | Posts: 21 | Joined: 10/09
Posted: 12/02/09
01:45 PM

Depends if you want to keep the same motor in the truck, and what you plan on using it for. I have a '73 chevy with a 4speed manual tranny and 250 inline 6. The truck used to be a 3 speed, but because of the engine's relatively low horse power, the swap was made. My other '75 chevy has a 3 speed, but a 350 V-8, which has plenty of power, and is more economical (fuel wise) than if it had a 4 speed. 4-5 speed swaps though will require you to cut out a section of the floor to accomodate the larger transmission.One cool tip though is that if you keep the same gearing in the diferential, no matter what the gearing will be faster. As for the id numbers, I'm sorry I can't be of any help.  
'73 C-10/ 250 L6, 4 speed
'75 C-10/ 350, 3 speed`
`91 Silverado 1500 4x4/305tbi auto

PackRatWrecker PackRatWrecker
Enthusiast | Posts: 262 | Joined: 09/08
Posted: 12/02/09
08:25 PM

Sounds like you have an SM318.  Not bad, for what it was, small, light, etc.  Not good for any kind of performance application.  1st gear ring blows up rather easily.

Swapping in a Saginaw 3 or 4 speed is a good idea.  A little linkage massaging & shortening the driveline, should be all the major issues.  Look for one with 3 lines around the input shaft.  That is the wide ratio unit with a 3.50 1st gear.  
1949 Chevy 1 1/2ton, home-built hydraulic wrecker.  Rustoleum industrial black, with flames.  Flamethrowers out 5" dual stacks.
1962 Chevy C-20, 402BB, 4-speed, 3.90 positrack. Hauls my camper.... among other things.
Kaiser M35A Deuce, 4x4 4 wheel steering *work in progress*

65C10Fleetside 65C10Fleetside
New User | Posts: 5 | Joined: 08/09
Posted: 12/23/09
09:59 PM

Thanks you guys for the input. I will be keeping the 292cid, currently adding long headers, Clifford water heated intake and just purchased Holly 390 cfm carb. converting to manual choke. Truck will be daily driver with light towing. undecided on direction to auto or manual trans. rear end has 3.73 gearing, 41 tooth Ring. requesting info on posi setup.