Transmission Swap Options

[r32skyliner]

Hello folks.  I have a 73 Cheyenne with a 350 and either the THM350 or 400.  Not sure but I know it's a 3spd.  It's going to be my son's first vehicle and I want to swap the tranny to a 4spd so it's not costing him his paycheck in gas.  Do you guys have any suggestions on what to go with?  From what I have read, the truck also came from the factory with a 700r4.  I've also read that the 700r4's came in 27 and 30 spline versions.  Any suggestions on another tranny like the 4l60/80 maybe?  I'm an aircraft mechanic by trade so I can turn a wrench but I'm still in the learning stages on vehicles.  Thanks...

[zieg85]

Welcome first of all from NW Indiana.  A 700R4 would be a good choice for an upgrade but probably won't be much of a difference in gas mileage to really be worth the upgrade unless your current transmission is on its way out.  If the transmission is in good shape, tune the truck and run it the way it is, check mileage and we can go from there.  A well tuned easy driven 350 with a TH350 and normal gears should get 10-15 mph.  An overdrive isn't going to help the around the town much and may only give 1-2 more on the highway.   How is the truck going to be driven?  Mostly highway or city?  What does it fair now?  Is it a 4x4 or not, 1/2 ton or 3/4 ton?

[Blazin]

Welcopme from New Hampshaa. X2 on what zieg said.
The little bit you might gain would be allot of time, and effort spent for little return. Would take quite a while to pay for itself. Also as zieg said the only place you would notice is in longer distance, or highway driving. Any 16 year old I know may be behind the wheel the better part of their waking hours, but useually its running around to buddies houses, after school stuff, or to a job.

Couple things I would look into is what does it have for rearend gears now?
If they are on the low side like 3:73 or something in that area. I would try a little taller tire. You could go to a 265/75, or 265/85 tire. This would raise the overall gear ratio a bit, and probaly not make the slow speed, or out of the stop light power suffer much at all. This to would probably not gain you alot per gallon. On the other hand the small gain you might see would pay back alot quicker than swapping a differnt transmission in. Plus the wheel openings of these truck are begging for bigger rubber, it would be an asthetics gain as well. Maybe even some nice wheels too?

[bake74]

     Welcome from California.  Basically as stated before.  The standard will net a couple miles per gallon as long as your son can keep his foot out of it. (in my experience, teenagers, especially males like to go fast )  There is all the parts that you have to collect to swap from auto to standard.
      A 4le60/80 also will need wiring and the cpm controls to go along with it.  In that case I say wait till it needs a engine or trans and do both together. 

[Blazin]

I think he is thinking 4 speed automatic?

[1979C20]

     Welcome from California.  Basically as stated before.  The standard will net a couple miles per gallon as long as your son can keep his foot out of it. (in my experience, teenagers, especially males like to go fast )  There is all the parts that you have to collect to swap from auto to standard.
      A 4le60/80 also will need wiring and the cpm controls to go along with it.  In that case I say wait till it needs a engine or trans and do both together.

I think he is thinking 4 speed automatic?

Hello folks.  I have a 73 Cheyenne with a 350 and either the THM350 or 400.  Not sure but I know it's a 3spd.  It's going to be my son's first vehicle and I want to swap the tranny to a 4spd so it's not costing him his paycheck in gas.  Do you guys have any suggestions on what to go with?  From what I have read, the truck also came from the factory with a 700r4.  I've also read that the 700r4's came in 27 and 30 spline versions.  Any suggestions on another tranny like the 4l60/80 maybe?  I'm an aircraft mechanic by trade so I can turn a wrench but I'm still in the learning stages on vehicles.  Thanks...

He talked about the 700r4, but im not sure if he was wanting to swap one of them in, or an SM465

[Dr_Snooz]

I would start by looking at the rear end ratio. It's much easier and cheaper to swap out a diff than to swap a trans.