Some questions about a 1988 GMC C7 .

So...

Here is a video of the old thing running. Right after we put the diesel tank back on (cleaned, de-rusted, primed and painted, along with its mounting brackets and straps)... along with new rubber sections of fuel line and a fuel filter.



Luckily... the only trick we did was to fill the new filter with fuel... no other special fuel system bleeding. Better to be lucky than good. Cleaning up the tank and filter (the filter hadn't been changed in years, by the looks of it)... cleaned up the emissions a ton. When it was driven into the yard, by the person that I bought it from, it smoked like a forest fire...

Anyway. Here are some remaining "quirks"...

First some info.

Detroit 8.2L diesel

GVWR is 27028lbs
Was originally a dump.
About half of the dump truck mechanicals are there... but it's converted to a flatbed stake, at the moment. (although... whoever converted it didn't think about clearance for the rear tires; when you drop the bed down without the rail that the dump bed pivots on, on top of the chassis frame rails...)

9 x 20 tires, fronts say that they are rated at 80PSI single or 70PSI dual. (They came to me with about 40PSI... I have them at 70PSI at the moment).

I'm still learning about how to manage the duals. The extension on the driver's side, inside dual appears to have been knocked out of place. It's stuck back out of position, instead of poking through the outside rim. I bought a couple of parts for the inflation gun on the compressor in my shop... I haven't put them together and tried to get at that extension yet. I'm curious about this, because I road tested it (it's registered and insured... I have the 10 day temporary inspection to work with)... and it acts as if a tire has either a flat spot from being parked... or it's out of balance... or underinflated. Hard to describe... but... I'm familiar with tractors; if you park a tractor overnight on a cold night... the tires take a set; and the whole machine does a little "limp" or rocking action from side to side... until the tire warms up and gets back to round. This got MUCH better when I adjusted the pressure on the fronts... I'm wondering if there is a little bit of problem left with the rears.

About that road test. It seems that somebody disengaged the axle shift. It's always in low axle, regardless of what I do with the button on the shifting lever. I can probably just follow the linkage for that and check to see where it goes.

The brakes work great, and the pressure system appears to work fine. I'm an engineer and a farmer, not a diesel mechanic or truck driver; so I haven't done a "leakdown test"... yet... but it holds. I will do a leakdown test soon...

It actually holds "too well", because the parking brakes don't activate, even when I pull the button to engage. There must be a solenoid somewhere... or a valve.... any hints where to look would be appreciated.

The dashboard is a random blinking lights show, no fuel gauge (the sending unit is fine and connected, we checked that, when we did the tank and ohmed it out...)

I was looking for a fuse panel to start pulling dashboard fuses; but I didn't find a panel... what I found is a system of terminal blocks on the engine side of the firewall just forward of the steering wheel. I'm wondering if this vehicle uses inline fuses?

Any hints on where I could find a general wiring diagram? I'm an electronics engineer, and I have a pretty well stocked "lab" in my garage with soldering and terminating tools/equipment... I don't mind re-making wires or even harnesses... I just need some sort of general reference...

I apologize in advance if this novice-type of questioning isn't welcome here where real diesel mechanics work... I'm not trying to take work away from y'all... this is going to be a farm truck... I just want it safe and functional, as much as possible.

Thanks!

 

I posted some initial questions about this a couple of months ago. If anybody is curious about the delays? Took two months and four days to process a title/registration request with the post-COVID NYS DMV.

 

Thanks, that gives me at least a foothold of looking at the axle shift. To be honest, I'm not sure if I care. But, even if I don't need the axle shift, I want to know why it isn't working... Sort of like the dashboard. The overheating dummy light comes on at random times, along with its alarm beeper. I now know that the engine isn't overheating... it's a wiring/dashboard issue. So, even though I haven't fixed it yet, I know that it isn't any emergency...

 

And yes... to the dumping flatbed. When I saw this for sale along the side of the road, that's what I thought.... dumping flatbed. What could be more handy than taking some construction debris to the landfill and pulling a dump lever? A friend of mine said... "get a dump trailer".... yeah... and with the 18" dump height... you need a quarter mile to dump a twenty foot load... no thanks...

I'm actually pricing the steel to make this a dump again... for what I bought it for, I have some wiggle room.

 

To each their own... but when the deck is 18" off the ground, the pile can only be so high... and even nearly vertical... It takes a long runway to dump a full load. Unless you can get past vertical and flip right over... (which is what agricultural silage dump wagons do.. they hinge at the top.

But anyway. If you already have a pickup. A dump trailer is a great option.

I don't have a pickup... I went straight to the big, old truck.

 

So, here are some pictures of the brake systems around the rear axle...

 

Some pictures of the rear rim.