hunting truck questions

[jarhead76]

i have 76 K20 camper special with a 350 and a 700r4 trans. i would like to use this truck for my camping and hunting adventures but she rapes me on gas in the ball park of 8- 10 MPG's and 4 wheel drive is even worse.  i hoping to get a little more mileage out of her but still keep the power. now the transmission is staring to slip a bit in reverse and park is shot to heck so its time to change the any way. is there a better transmission for what i would like to do. also i am going to need a new carburetor soon what would be the right one to do the job.

[Irish_Alley]

didnt know 76 came with a 700r4. i would keep the/a 700r4 if thats what you have. if you switch trans then you have to think about transfer case and drive shafts. if you do want to swap you have to think about how you drive it. i love stick shifts but they arnt really good for highway unless you get a od unit like nv4500. but they can be a little pricy then again you have to think about changing the transfer case to the passengers side or puting in a different front axle and again drive shafts

[Jason S]

Are you sure you have a 700R4 overdrive transmission? That transmission would've been swapped in at some point. 

As a direct comparison, my '73 GMC K2500 gets 10 mpg (on gasoline) with a TH350 (no overdrive) and 4.10 gears... 

[jarhead76]

yes its a 700r4 it was pulled out of a blazer by the previous owner some years back.

[werewolfx13]

In most cases, a 700r4 is going to be best bang for your buck for mileage/useable strength in these trucks. My recommendation is as follows:
Rebuild the 700r4, there are tons of guides to building them for extra strength
Get a rebuilt q-jet carb, or have yours rebuilt. Mileage and driveability is generally better with a well tuned qjet, at a wider variety of conditions.
Go with 3.42 or 3.72 gears in the front and rear ends
Is the transfer case an np208? it should be, given that its behind a 700r4, but if its not, swap to one. They're not as strong as a 203 or 205, but besides the fact they're a boatload lighter, with less rotating mass, they do better on mileage and are strong enough to be used, just not completely thrashed on.
Stick with a reasonable tire size, 265/75r16 is a fair balance between ground clearance (adequate for most logging roads, etc) and rotating mass. Something with a lower rolling resistance will boost your mileage, especially on the highway, but will be a tradeoff in traction.

With a properly tuned carbed 350, proper gear ratio, and a 700r4 you should be seeing about 14 mpg on the highway. I slap the snot out of the loud pedal on a regular basis, have the heaviest (in terms of weight) transfer case these trucks ever came with (np203), which is a full time case, and a non OD transmission, with 4.11 gears, mismatched tires with horrendous rolling resistance, an out of tune 305, and a 6.5'x 8'  wood floor flatbed with two 4' steel underbody toolboxes on top of the bed stuffed with 200 ft of cutting torch hose, two sets of regulators (one single stage, one two stage), 3 different torches, a basic hand tool set, various welding/cutting tools, plus my 40 lb horizontal LP tank for my cutting torch, "K" oxygen bottle, #4.5 acetylene bottle, a 600# capacity steel dolly, and a cooler that at any given point has about 20 lbs of ice, 20 lbs of water, and 20 lbs of beverages in it...And still get 4-8 mpg. If you're getting 8-10 with that transmission, you're getting hurt by the tuning and slipping trans, or someone filled your right shoe with concrete while you weren't looking.

This is mostly my opinion, as such is worth varying amounts depending on who you ask, but most people are cheap and wont pay me anything for it...thats my story and I'm sticking to it. 

[jarhead76]

thanks for the info.
i guess my next question would be how do i tell what transfer case do i have.  also she has a 14bolt rear end so how would i figure out what gears i have. 

[werewolfx13]

Theres a metal tag on the transfer case, I'm a few too many into my barley pop to remember with clarity where the tag is. If its missing, you can also tell by the case composition. np203 is chain driven, all cast iron case with an aluminum chain cover. Np205 is an all cast iron gear to gear case with a cast iron cover plate. Np208 is an all aluminum chain driven case. Np203's are MASSIVE. the chain housing is overwhelmingly large compared to an np208.

As far as rear end gears, the only definite way is to pop the cover and rotate the gears. The ratio is stamped on the ring gear. Also, you can count the teeth on the ring and on the pinion and figure it up that way.

[jarhead76]

i figured that was the case with the gears well its time to change the gear oil anyway.

[jarhead76]

its a Np203 T case.  I think I'm going to keep the T case, rebuild the trans, she needs a tuneup. that leaves me with what corroborator would be best werewolf said a q-jet. what would be a good one to use the most bang for the buck as it were.

[Irish_Alley]

for a stock/near stock motor you dont need over 600cfm if you want aftermarket. but a quad can flow i think up to 800 cfm so i would stick with it, you will never need that much and your just waisting your money. buy a rebuild kit idk for $20-$30? check the bushings on the butterfly for and leaks this is a common problem which will cause a vacuum leak and high idle

[jarhead76]

i am missing one of the butterfly valves the front one. i was told t was for the cold start. but I'm not sure. some one replaced the old 454 it came with and dropped in a 350 and did a piss poor job of it. would i be able to get a new one in a rebuild kit or would it be a full replacement thing and if Im lucky pull a part.

[Irish_Alley]

the butterfly wouldnt be in any rebuild kit that i know of. not even sure if they see just the butterfly. is the rod still in place? you could also go to a junkyard and get a carb. you might have to rebuild it but i dont see one costing more than $20. then a rebuild kit for another 20. so you will be way less than a new carb would cost

[werewolfx13]

Sure its not the choke plate you're missing? The butterfly valves are in the bottom of the carb, only way to see them is to look past the choke plate and down the primaries/secondaries...or remove the carb.

[Irish_Alley]

im thinking its the choke plate also. some remove it cause they are having problems with how its working and figure it will run better without

[jaredts]

Just find a quadrajet from a truck or van in a junkyard and rebuild it.  Just make sure not to get a computer controlled quadrajet.  I'm happy with my Edelbrock 1406 however, and it is very popular.  I don't think I'm losing significant mpg's, but I don't really check it either.  I just know it seems decent for a truck.