1975 GMC 6500 dump truck with 366ci gas big block

[Verticaltrx]

Just a comment from the cheap seats. This is an interesting forum to follow. On one side 650 foot pounds of torque aren't enough for a 3/4 ton diesel p/u. On the other, members see the merits of a vintage dump truck powered by en engine that today would be considered patheitc & weak for even a compact P/U. It makes you wonder how our parents & grandparents accomplished so much with the equipment they had at their disposal. I'm not trying to pick a fight, just amazed how capable our trucks, tractors, powertools etc.. have become

Comparing any 3/4 ton pickup regardless of engine size to a MDT is an apples to oranges comparison. These old trucks with the 350's in them were geared very deep and are putting way more torque to the axle than even the newest light duty diesel trucks. They wont top a hill as fast, but they will take off from a steep stoplight grossing 30K much easier. Our '75 C60 has a 350, sm465 and two speed Eaton (8.85 lo, 6.65 hi ratio) and on the low side of first gear you're sending over 20,000lb-ft of torque to the axle shafts. In comparison my fathers new 6.7 cummins 6speed 3500 dodge is only putting 12,800lb-ft to the axle shafts. Granted the C60 does have taller tires, the overall ratio is still better.


As to the OP's question, I would get the truck. Our '75 C60 (same truck basically) looks like **** but it sure gets a lot of work done. The only real downfall is the hydraulic brake system. While I don't agree they are exponentially expensive to work on they do have some downfalls. Also, there were several different types of systems on these trucks, but I haven't seen many with hydroboost as someone stated. Ours is a vacuum boost setup and it slowly 'burns' brake fluid. This was a common problem and chevy even put a sticker over the master cylinder that says to check the brake fluid every 30days. Not a big problem, but something to remember to check. We go through a small bottle of brake fluid every couple months. Overall a very solid old truck though, it will do 60mph on the highway against the governor, but a full load slows it down a good bit (32K gross). Gets about 6mpg empty, 4mpg loaded heavy.

 

[franklinute]

I have put many miles on a delivery truck with that setup. 366 or 427 engine 5speed tranny and 2 speed rear end. Usually 2 50 gallon gas tanks. In my experience these truck got 6-6.5 mpg loaded or not on the highway. We have owned several of these with over 200,000 miles. Engines are good and reliable. The middle cylinders tended to run a little rich so we inspected the plugs every 6 months. As said before at this age check the brake lines for any corrosion. I know of a local farmer who carried fertilizer and had a brake line rupture due to corrosion. The hand/parking brake needs to be in good shape. Other than that you have found a gem for around the farm short haul type of work.

 

[Dargo]

I crawled over it, under it, through it etc. and the following is a complete list of anything I could find. There was a small puddle under the hydraulic hoist cylinder about 3" in diameter. This is after the truck has sat in the same place for about 6 months. The brake lines on it have been replaced within the last 5 years. I forgot to look in his logbook for the date. The left front wheel and right rear wheel seem to have wheel cylinders that are weeping; not just moist, but not what I'd call a "leak". Right rear tail light didn't work. Front brake pads looked fine, but I believe the rear brake pads would need to be replaced soon. Wipers looked to be dry rotted.

Otherwise, no rust anywhere, the bed was in exceptional shape. The only time he hauled rip-rap in it, he had them put about 6" of sand in the bottom of the bed first. Bed floor is original with no holes or even many ripples between supports. Entire truck has been media blasted and painted with some durable enamel paint because it apparently was the same color truck as one of his competitor's. It has never been in a wreck and has never sat outside since he bought it new. I do have room in my 80X120 barn, so if I buy it, it will continue to be stored indoors. Tread on all 4 rear tires are "okay"; not great, but not bald and they all match. Front tires look good. Most surprising was that I couldn't find any oil leaks from the engine or transmission and neither have ever had any work done on them. Exhaust is about 15 years old, but doesn't look to be ready to rust through anywhere. All shifts were fine, including rear axle, and seemed to stop fine. Has ugly white mud flaps on a green and white truck with a black bed.

I still made no decision and plan to test it tomorrow when he gets a load of #11 gravel for his driveway and see how it handles a load and how the dump works under a load. It has the big hump in the front of the bed with a 3 stage cylinder rather than some scissor type lifts I've seen.

 

[scoutcub]

I crawled over it, under it, through it etc. and the following is a complete list of anything I could find. There was a small puddle under the hydraulic hoist cylinder about 3" in diameter. This is after the truck has sat in the same place for about 6 months. The brake lines on it have been replaced within the last 5 years. I forgot to look in his logbook for the date. The left front wheel and right rear wheel seem to have wheel cylinders that are weeping; not just moist, but not what I'd call a "leak". Right rear tail light didn't work. Front brake pads looked fine, but I believe the rear brake pads would need to be replaced soon. Wipers looked to be dry rotted.

Otherwise, no rust anywhere, the bed was in exceptional shape. The only time he hauled rip-rap in it, he had them put about 6" of sand in the bottom of the bed first. Bed floor is original with no holes or even many ripples between supports. Entire truck has been media blasted and painted with some durable enamel paint because it apparently was the same color truck as one of his competitor's. It has never been in a wreck and has never sat outside since he bought it new. I do have room in my 80X120 barn, so if I buy it, it will continue to be stored indoors. Tread on all 4 rear tires are "okay"; not great, but not bald and they all match. Front tires look good. Most surprising was that I couldn't find any oil leaks from the engine or transmission and neither have ever had any work done on them. Exhaust is about 15 years old, but doesn't look to be ready to rust through anywhere. All shifts were fine, including rear axle, and seemed to stop fine. Has ugly white mud flaps on a green and white truck with a black bed.

I still made no decision and plan to test it tomorrow when he gets a load of #11 gravel for his driveway and see how it handles a load and how the dump works under a load. It has the big hump in the front of the bed with a 3 stage cylinder rather than some scissor type lifts I've seen.

Definitely sounds good for a 36 yr old vehicle, and a testament to how this guy takes care of his stuff! Be interesting to see how it "pulls" I bet it will be like a tank with that gearing.

 

[Mace Canute]

I'd buy that truck in a heartbeat.

 

[crazyal]

It has the big hump in the front of the bed with a 3 stage cylinder rather than some scissor type lifts I've seen.

Mine has the scissor lift but it puts a lot of stress on the dump frame. Fine for a new truck but not so much when they get old. I had to replace one of the rails for the dump frame that mount to the truck frame.

Chances are the hydraulic pump is mounted to the transmission. If it is it makes gate spreading a little difficult since when you push the clutch in the pump stops. You'll learn to raise the bed and get ready to push the clutch in quickly, put it in gear, and start moving once gravel starts coming out. When you go to get gravel you may want to see how your friend does it.

Too bad you were closer and looking for a project. I have an old 4wd fire truck with about 20K miles on it. I've used the cab and motor for my dump truck but I still have both axles and the divorced transfer case (they are hydraulic brakes while my dump is air). I would love to see a nice truck get converted to 4wd.

 

[capt_met]

i say buy it fast. these trucks in very good condition easily bring $3500. i have a 79 chevy C65. it has the same 366 with split rearend. none of the repairs including brakes have been very expensive. in fact i have found parts very reasonable from NAPA. they are basic trucks but in many ways much better than newer ones. not as pretty but the mail gets delivered. the 366 is a beast of a gas engine. high torque for a gas engine and with the gearing you will have no problems. i tow heavy equipment with mine and it does fine, generally able to keep up with traffic. long grades are not a problem either as long as your not in a hurry. empty i get around 6 mpg and get up 65 easily. loaded it is getting paid so i don't worry about the milage. this truck has earned it's keep and i'll run it till the wheels fall off.

 

[Dargo]

Too bad you were closer and looking for a project. I have an old 4wd fire truck with about 20K miles on it. I've used the cab and motor for my dump truck but I still have both axles and the divorced transfer case (they are hydraulic brakes while my dump is air). I would love to see a nice truck get converted to 4wd.

It's funny you say that. One of the first things I'll have to do is weld some bid D rings on the front and back. Since I'll be using it off road almost all the time, I figure I'll get it stuck with a bit of frequency. At least that's what happened with my last 2 dumps I ran off road a lot. Having 4 wheel drive and an air locker in all the axles would be the ticket for me.

 

[Dargo]

i say buy it fast. these trucks in very good condition easily bring $3500. i have a 79 chevy C65. it has the same 366 with split rearend. none of the repairs including brakes have been very expensive. in fact i have found parts very reasonable from NAPA. they are basic trucks but in many ways much better than newer ones. not as pretty but the mail gets delivered. the 366 is a beast of a gas engine. high torque for a gas engine and with the gearing you will have no problems. i tow heavy equipment with mine and it does fine, generally able to keep up with traffic. long grades are not a problem either as long as your not in a hurry. empty i get around 6 mpg and get up 65 easily. loaded it is getting paid so i don't worry about the milage. this truck has earned it's keep and i'll run it till the wheels fall off.

Thanks for the reply. I've been a gearhead my whole life, but not much so with dump trucks. I really am unfamiliar with the 366. I assumed it would suck on fuel. My wife always complains that our RV sucks on fuel. Well, I sort of expected that with the Cat C9 in the back pushing what amounts to about 3 4X8 sheets of flat front through the air. I can get up to about 10 mpg with the coach if I'm only running 60 mph and doing 1200 to 1400 RPM. As long as the old 366 has a good rep for being a good engine, that's all I'm concerned about. If it's similar to the 427, and I've just heard that and don't know for a fact, that would be good since they have proven to be workhorses.

What's so funny is that it's not much money, relatively speaking, yet I seem to be looking at this more than I've looked at vehicles costing 20X as much. LOL

 

[Hooked_on_HP]

What's so funny is that it's not much money, relatively speaking, yet I seem to be looking at this more than I've looked at vehicles costing 20X as much. LOL

This means you really don't need it. You want it because it is a great deal but common sence is winning out.
Bill