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Free C20, best tranmission setup

Bowtiek10

Bowtiek10

1/2 ton status
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I'm in a position to get a free 76 C20 Camper Special. Its in Ok shape, been sitting/mired for some time now. It was parked because the th400 needs rebuilt. The 350 has good compression still. I would use the truck as a beater/workhorse for work on the house or things of that nature.

Problem is: 4.56 gears.

So, whats the best bet to get this thing as a workhorse that can be driven at highway speeds. I was thinking a 4l80E retrofit with a transmission tuner, or just do a cheap rebuild/shift kit on the th400 and potentially a regear to a 3.73 down the road.

What would you guys with experience do with a truck like this?
 
some highway use but mostly around town to me = th400 and 33" tires on them 4.56 gears . at 70 mph its 3400 rpm . 3.73 is 2800 rpm

i run my k30 with 4.10 and 33" tall tires and am o.k. with some highway . i would prefer the overdrive but didnt do it on this truck .
 
Agreed, honestly answer how much highway use. I would think a 14bff gear change would be cheaper than going 4L80, controller, driveshaft. IF you can rebuild the 400, kits are only a couple hundred, and a new gearset 3-400?
 
Thanks for the replies.

Where I live in Colorado, you pretty much have to get on the highway 25 miles in each direction to get major stuff. I don't need a rocketship, so 70-80 MPH is perfect. I think setting up with taller tires is a good thought for sure, although I don't want to pay through the nose to get this thing going. I'd prefer to just throw road tires on it, not to expect to drive it in the winter here (it will need tires). What do rebuilds usually run with a shift kit? I don't like to rebuild transmissions/transfer cases. Also what would a gear change run? Preferably posi
 
I would say you could get the trans done for 5-700 if you took it out, gear change probably a bit more if diff is in good shape, posi/locker depends on what’s in it now, I’m assuming it’s a 14BFF?
 
76zimmer said:
I would say you could get the trans done for 5-700 if you took it out, gear change probably a bit more if diff is in good shape, posi/locker depends on what’s in it now, I’m assuming it’s a 14BFF?
Click to expand...

14BFF Yes. 3.73 posi would be my preferred setup with your average-joe 31in road tires. I would like to pull a little flatbed bumper pull with it too on occasion
 
@Wes Harden has a good idea there. I believe that the carrier split is between 4:10 and 4:56, so you could get into and axle with the proper carrier to install 3:73 gears without buying the posi at the same time if you wanted to.
Just an idea.
 
It's possible you could get a 4.10 carrier and maybe even a set of used gears from someone on here even maybe.. that'd probably be the cheapest route. Should be someone on here that at least has the carrier. Then do some cheap 3.73s from amazon.
 
I know a guy who has a '63 K20 GMC Stepside with 4:56 oem gearing and a SM420 4 speed...and a 327...

He doesn't drive it much on highways,but to get to some truck shows he would have to go 60+ miles ,and feared it would toss a rod it revved so high trying to keep up with traffic at 65+ mph..

To reduce its rpms on the highway,he just put 4 of those military 37" Goodyears on it and he says it'll cruise at 65 now without sounding like it's screaming like before..he did have to tweak the front fenders at the bottom lip to fit them,the rear they cleared fine with no mods..
Bigger tires are poor man's overdrive!..
 
look for a k20 14bff complete, chances are it will be 4.10 or lower numerically, and have a G80 gov lock, these are ok in the 14 bolt. I bet the whole axle can found under 300. rebuild the 400 and put 33+ tires on rear
 
1980's diesel powered 3/4 tons like mine often had the highest gearing,I have seen some in salvage yards in the past that had 3:23 and 3:42 ratio 8 lug rears..mine might be one of those 2 ratios,it'll hit almost 60 in second gear when it hits the governor and you wouldn't be able to do that with 3:73's or 4:10's..
 
This may have to go on the backburner for a while, picked up an 03 cummins 6 speed as the workhorse for 2600.
 
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