Transmissions

[macdodd]

Ok,,,,so I'm thinking about putting another trans in my truck. Its got a 350/305 heads. Its got a 3 speed auto, older trans. in it now. Want something with a overdrive,,,better milege, better road speed. So what are the suggestions? Its a '69 c-10.

[hugger6933]

700R4 would probably be the most popular choice. It was found behind motors in a bunch of the Generals stuff from 82 to 94 in everything from S10's to Corvettes and also in the 1/2 ton truck, blazer, suburban and so on.
The 700 takes the same drive yoke that the TH 350 does and the 3 speed I think and also the 2 speed power glide trans. the Trans is longer and will require the crossmember to be moved and the drive shaft shortened. Jim

[leftybass209]

No offense to you, but this topic is covered pretty regularly. If you use the search function you'll find a lot of great information on manual and automatic overdrives. Your basic options for auto are 700r4, 2004r, 4l60e, and 4l80e. There's differences in all of them.

[macdodd]

No offense taken,,,,I'm new at this,,,,just bought the truck the first of the year,,,,so any suggestions help,,,,

[macdodd]

Chatted with a guy that does rear ends for older trucks. He said if the 3 speed auto thats in it isn't broke don't fix it,,,,LOL. He's gonna pull the cover and check the gears and we'll go from there. At 50mph,,,I'm running @2200 rpms.

[MAC71]

I have used a 700R4 in my 71 C10 for 18 years, hot rod with it(mid 13's in the 1/4) towed with it and it has 300,000 miles on it. It works!
That being said its not stock and it is a 30 spline, not a 27. Also I have a 3.73 gear but you would not want any thing lower than a 3.55 gear. If you have 3.07 gears your going to lug the engine even at 70 mph. The big negative is there is a big spred between 1st and 2nd gear, but first gear is so low it makes anything a tire smoker and makes it easy to get a heavy trailer moving.
At 70mph I am at 2100 rpm.
You did not state the transmission you currently have but its most likely a th350, but if its a th400 and you need the strength but really want the over drive you could add a gear venders overdrive. That is cheaper and easier than a 4L80.
At 70 my truck gets 17 mpg in over drive in 3rd it gets 11 mpg.