our [dilapitated] truck

[magnethead]

We own a 1977 GMC C-30 Camper Special 2wd, and need help. Lots of it. And Then some.

It has the 454 motor with TH400 and 4.10 gears for climbing steep slopes. We have installed headers and replaced the entire audio system. We've sandblasted and primered the bed (you should have seen it..even primered it looks 100 times better), put tiniting on the rear windows, and put seat covers on the seats.

Those are the good things. Here's the bad things:

5-7 MPG
Body cancer under drivers door
cracked right side fender
bent hood
no battery retainer (bunjie cord holds it, its about to break)
weighs 7000 pounds
drivers mirror is missing bolt / mirror is on verge of flying off
axle was run for 500 miles without any lubricant
rear drums need replacement
no OD
no headliner
AC/heater doesn't work
many things i'm forgetting

The guy we bought it off of back in the mid 80's used it to pull a race car cross country, and we used it to take our race car (loaded trailer weighed as much as the truck) up and down the west coast. In 1995 we moved out here to texas and took it down to ennis and sanger dragways a few times before selling the race car and trailer. We still use it as a farm truck and tow our boat with it, along with trips to home depot about once a month or so. With all this, the odometer has rolled over twice (maybe 3 times, nobody knows for sure), and the whole truck is wore out.

oh, and yes it has a quadrajet (or quadrajunk as i've heard it called)
Here are a few pics

[SCOTI]

It just needs some TLC.

[bigblock73]

Looks pretty solid to me. I hope to own a 73-87 dually someday, they are great tow/work rigs.

5-7 mpg sucks, but once you get it tuned up and running right, you should at least get 10 I would assume. Also, you could put a Gear Vendors under/over drive system on it and have six speeds and get better mpg!

[784X4GUY]

I knew a guy back home in Indiana who had I believe it was that same year. And he cleaned the body up. Shaved the door handles and drip rails painted it purple and Lowered it and put a 468 BBC in it. That thing was bad it would smoke them duals with ease. I loved the look of that truck. But anyways good luck with yours man...Later Mike

[TrainD5115]

I had problems with my camper style mirrors too. Ended up scrapping the original screws in favor of bolts with a washer and nut on the inside of the door. You have to remove the door panel for this but it beats having to tighten screws every couple of days. The battery tray is easily replaceable too as long as the surrounding metal is in tact. I am only getting about 8 mpg out of my 350/350 combo with the quadrajet 4bbl. and while this sucks and would love to have overdrive its a little out of my price range right now. I guess if we were really concerned with fuel mileage we would all drive Geo metros right. Good luck on your up grades.

Train

[magnethead]

if we had the money, the very first mod would be swap the TH400 in favor of a 4L80E, since it's the direct OD replacement. Only modification would be the wiring..thanks to the people at GM, thats the easy part, providing the 4L80E has automatic overdrive, not manual.

BB73- lots on info on your site, thats how i wound up here!

I can tell the engine is wore the smack out, but it runs. It's got a cooler for everything, The radiator spans the whole width of grille from headlight to headlight and we put transmission and oil coolers on it.

They sure are good towers, that racecar we towed, the trailer when loaded weighed 8000 pounds (1000 more than the truck) and we took it up the grapevine in california once at 55 mph.

the GVWR is 10,000 pounds, the truck weighs 7000- we cal haul a ton and a half in the bed...don't think thats been done to it yet, but running that dana 70 without oil (it had a pinion seal leaking and we didnt know it) for as far and long as we did is sure showing, that axle whines when it gets into the higher speeds.

Does anybody know what gear design it has? Straight teeth or the more modern curved teeth? I've been told both ways.

I don't know what all we can do on our budget to gain mileage, but i was tolds the '77 dually 454 came with 8:1 and 10:1 compression from the factory. The entire motor is stock other than the oil cooler and headers, and the stock exhaust past the headers (1.25" pipe, 2" tips??). It has the stock convertor (2300?), and we've replaced the distributor, plugs, and plug wires as normal maintainence. We're thinking about a custom cold air intake from under the bumper so the motor doesn't breate that hot air in off the block.

Also, the wood grain plastic dash is starting to come apart, and there is a nice pretty bundle of wires that hang right above the gas and brake pedals... and we have no clue where it came from.

[magnethead]

if it wasnt as cold as it is out, i'd get newer pics (those are well over a year old)

[SanitysBane]

get a good after market intake, and a good header back exhaust, and tune the carb up really good, u should be able to get 10 out of easily. we tuned up a 73 to get 17 towing our race car, trailer(4000-5000) and about 1,000 pounds of tools and crap in the bed, with the ac blowing.

[magnethead]

I think we bought a carb rebuild kit and rebuilt the carb in 2000, it was either for my moms camaro or the truck (we only have 2 vechicles with those ancient things called carburetors), so it was most likely for the truck. A new intake is out of the question, we dont have an extra 300+ bucks for one of those.

The stock exhaust isnt very restrictive-it's mostly just a straight pipe to the muffler and back to the axle, where it has that hump as usual, then it's straight again to the side dump. I don't remember if it has a crossover pipe, but theres no catylitic, so the only restriction can be the mufflers (which OEM mufflers are pretty notorious for backpressure), considering the exhaust only has 3 bends.

There is a little bit of blue smoke that comes out on startup (indicating blow-by) but none that can be seen when it runs warm (as the piston rings expand).

[Prerunner1982]

the pipes maybe straight but the 1.25" causes enough restriction on its own.... 2.5" duals would work nicely.

[SanitysBane]

for a big block i would run 3 inch dauls, personally, and a new intake manifold can be had for about 197.95 from summit racing, thats the Weiand Stealth.

[magnethead]

just went out and measured...exhaust is 2" pipes with 2.5" tips. attached are some updated photos i just took. EDIT: Yes it's Dual Exhaust

note the body cancer and mirror.

(the line on the hood is a shadow, not paint)

[magnethead]

i just saw something- on the emblem (you can see it in the last pic) it says 35..so is it a C35 or C30? I never noticed that.....

[MylilBowTie]

might be a replacement fender or something. GM does the one up thing like C15 C25 C35 S15 things like that chevy does C10 c20 C30 S10. But there might be a little play in between the two. Just what I have picked up on. With GMs more upscale promotion over a chevy they want bigger (higher) number series I guess.

4L80E is longer than a th400 (4in tailshaft) that is the shortest besides th400 for a 4x4. HD 4L80E is 31 15/16 long (5 15/16 inch tailshaft), Normal 4L80E is 32 11/16 long (6 11/16 inch tailshaft), Longest 4L80E is 33 inches (7in tailshaft). TH400 shortail (4in) is 28 3/8s, Th400 9inch tailshaft 33 27/32, Th400 long tailshaft (13 inche tailshaft) is 37 7/8.

4L80E is about a 3500 (round about figure) investment. By the time you get the transmission, transmission controller, oil cooler, driveshaft length setup.

On the gas mileage I get about 11.7 355 "rv" cam 4bbl, th400, 3.08 gears and 29.5 in tall tires in a half ton 2wd.

[magnethead]

well it's a GMC, so it'd be a C35, not C30?

[magnethead]

oh btw something else i just found out: it has hydroboost and a pretty large brake booster...

something i've been thinking was swaping the big, heavy, wore out rear drums for 11" discs (16" rims - caliper spacing = 11") so it'll really have responsive braking (something you need on a 7000 pound truck). And it has trailer brakes installed already if we ever have a heavy trailer that can't keep up.

[cliffsta]

bah 10 MPG with a big honker like that, that would be something. I'm getting 11-13 with a 305 and Th350 with 2.56 rear gear. Could be that clogged up cat, or the ancient carb...but enough of my gripin'.
Good solid truck bud, mucho potential, you will go far

[magnethead]

so it's got dual 2" pipes, quadrajunk, hedman headers, no smog equipment, oil cooler, trans cooler, full width radiator, a pair of 20 gallon tanks, and the fuel gauge reads 1/8-1/4 tank off (we've never ran it empty except once when we caught it sputtering and switched tanks and floored it). What can be done to increase mileage using standard tools and very little investment? We run it on 87 octane and use a mix of 10w-40 and 10w-30 non synthetic at the same time for oil (we have the depot put in 40 and we top off with 30). Once we get further on a gallon, hopefully we'll be saving enough gas money it'll start adding up. Gear vendors wants 2400 + installation for an overdrive unit, certainly not cheap.

How much can these save individually and as a group?

Cold air tube to bumper
rebuilt/tuned carburetor
electric fans
hi-flow mufflers
aluminum rims (steel ones are rusting anyways)(weight saving)


math indicates it's spinning at about 2700 RPM at 60 mph

[MylilBowTie]

Cold air intake wouldn't hurt, depending on how cold it get in your area.

An out of tune worn out quadrajet can use up a lot of gas as opposed to one that is tuned and working correctly. They can be rebuilt, its a pain though for me anyway but not that hard. Only problem is if the quadrajets throttle bores are worn out and things like that even with a good rebuild its not up to specs. They can have bushings installed to get it back in spec. Warpage is also another problem with them, depending on the life its seen (over torqued).

Electric fans wouldn't hurt but I don't really see any gas mileage gained by it.

Mufflers wouldn't hurt that will gain you a little something.

Rims are more of a want to item than cost vs gas mileage, weight savings doesn't hurt but the cost of 6 rims and tires do.

I don't remember the size tire you have on the truck but if possible you could get a taller tire that will lower the rpm some but not a lot.

I would do a compression check of the engine, vacuum gauge to read the level and any fluctuations in it, possibly adjust the valve lash, check for old rotted vacuum lines, things like that.

[Grim Reaper]

Rockers are about $17 each from J.C. Whitney. Plenty of fenders available. Should be able to get a rust free for under $50.
The reason the front fenders rust out at the bottom is crap like leaves and pine needles get in the cowl area at the base of the wind shield. rain washes it into the fenders and it collects there.

You MPG sounds about right for a Dually. The stock 454 DOES NOT like running faster then 3k. They start sucking gas big time. A OD tranny will get you up to around 12. If you can keep the RPMs at 2500-2700 RPM is where it will get the best MPG. My 88 fuel injected 454 Burb will get 11.5 EMPTY at 75mph with no OD and 3.73 gear turning about 3100 RPM. I can tow 7,000 LB set the cruise at 2600-2700 RPM (65) and it will get 10.5. 454 stock is a low RPM motor. Get a 4L80 or a Gear vender's or similar OD. and that will help bring up the MPG.

Looks like a good truck that just needs a little TLC and some rockers to me.

[crossy]

I'm betting with the BB and 4.10's she'll still smoke-em, Pictures appreciated:-)

I'm also betting we can help with the heat/A-C dliema as it is REAL common for the blower stich to melt on the back side on the models equipped with A/c because of the amperage that goes through it . It is usually a simple fix.
DAVE

[magnethead]

well the problem with the AC/heat is more complex wiith that. the ducts are messed up, and what's mostly the problem is the air duct controller- the flapper in the ducts sticks. We tried moving it to be on heat and it worked fine, but when we moved the switch to A/C, the flap moved to the middle, so we had both goin simultaneously...

it just needs the entire duct and switch system removed and replaced with OEM parts.

[crossy]

there is a little plastic piece of crap on the one door that the linkage hooks to that is not available from anyone that I could find . That door controlled wher the air went ,so I reinforced with a small metal strap over the top of it to make it work. Also the ducts have foam insulation between each duct , that foam breaks down and lets all the air out behind the dash. I used cheap self sticking hardware store foam to restore the tight fit between ducts and the 75 really blew air out where it was supposed to after that. DAVE

[magnethead]

thanks for the heads up. I'll have to climb under the dash and figure what does what.

I'll get some pics of the interior things in a bit.

[MylilBowTie]

Its easier to open the glove box, take all the stuff in it out, then remove the glove box. Everything is right there.