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  1. 75gmck25

    Need advice on what to do.

    It is challenging to find a shop that wants to take on a small body repair job for a reasonable price. Big companies make most of their money from insurance repairs, and they have consistent business. Then there are the custom body work companies that want to do a complete restoration...
  2. 75gmck25

    Disconnected fuel line in engine bay

    As fuel is drawn out of the tank through the fuel line to the carburetor, air has to enter the tank to replace the fuel. And when the fuel expands during a warm day, you need to allow air to escape from the tank. The vent line and charcoal canister allows the air to go in and out of the gas...
  3. 75gmck25

    1979 454 C10, Factory Air

    The downside I found with the A6 is that all the ones at a reasonable price were rebuilt, and the first two I tried developed “Black Death” inside after a short time, which filled the system with black granules. I’m also not too crazy about the size and weight of the brackets used to mount...
  4. 75gmck25

    The old Fuel Gauge saga!

    Do you have only one tank and one in-tank fuel pump, with no 6 port fuel solenoid for two tanks?
  5. 75gmck25

    1979 454 C10, Factory Air

    No, but why do you ask? I’m not sure whether it’s good or bad if you think I am AI! I’ve been fixing and tweaking the A/C on my ‘75 K25 since about 2002, so it’s a long painful history. The latest set of brackets I’m using for the Sanden compressor are made by Alan Grove (purchased from...
  6. 75gmck25

    NP203 Oil Change

    That is definitely how your drain an NP203. Then fill with 30 weight oil until it dribbles out the fill port. Some guys tilt the truck on ramps and try to get a little extra oil in to help lubricate the chain, but I’ve never tried it. If it’s a converted NP203 you are supposed to run it in...
  7. 75gmck25

    1977 K20 audio

    The brand is Retrosound, and there are several models. I used one of their radios, a stereo center dash speaker (not much separation of left and right), and added 6x9s in the door. In hindsight, I should have just used the brackets and cab corner speakers instead of butchering the doors.
  8. 75gmck25

    1979 454 C10, Factory Air

    It takes a little searching, but there are kits to adapt and replace the old compressor and lines with newer compressors (usually Sanden). For example, the Pro6ten is an R134a Sanden compressor packaged as an exact bolt-in replacement for the A6. Some HVAC sites also sell adapters to bolt onto...
  9. 75gmck25

    73 K20 parking brake cable routing and hardware

    Most parts were missing when I got my ‘75 K25, but I used the setup pictured in the last post and bought the brake cable form LMC. I bought round rod stock from Lowe’s and fabricated the loops that hold the front corners of the cable out to the side. My frame already had holes in the right...
  10. 75gmck25

    Kind of a strange cooling system issue

    I suggest trying a Robert Shaw high flow thermostat from Summit. I have been using the 195 degree RS high flow thermostat for years and it has been very reliable. One additional note. I recently replaced it with a new one because my engine was not reaching full temperature of about 195. I...
  11. 75gmck25

    Signs of a failing proportioning valve

    I have a 3/4 ton K25 with 14 bolt FF rear axle, so pulling drums to inspect rear brakes is not easy. If I leave the parking brake set for anything more than a few hours, the rear shoes seem to take a set against the drums, and there is a significant clunk as they break loose. I usually have to...
  12. 75gmck25

    all time 4 wheel drive

    I have a 14 bolt FF with G80 locking differential, and I know how to shift my truck to 4 Loc. No problem with driving in mud and snow. You just have to understand how the drivetrain works.
  13. 75gmck25

    all time 4 wheel drive

    Definitely not an ‘85 truck. If they mixed and matched between years and did not notify DMV it may be difficult to get a valid title. Older trucks had a shorter VIN, it was not displayed in a window in the dash bezel, and they usually can’t be easily verified as valid with newer online VIN...
  14. 75gmck25

    Where's the resistor in the coil pink wire from ignition switch?

    If you are talking about the resistor for the ignition, it was only used to reduce the running voltage for points ignition. It is not needed with electronic ignition. If you see something inserted in your ‘87 harness it’s more likely to be a diode to prevent power feedback from one component...
  15. 75gmck25

    Wiring mystery

    The wires from the starter to the junction block have fusible links. A fusible link that is overloaded may burn out inside, but the burn is nearly invisible from the outside (maybe a bubble in the insulation). Or it may partially burn, leaving only a few strands of wire connected inside. I...
  16. 75gmck25

    Instrument cluster ground 87

    A 1980 is probably like my ‘75, where there is a single black panel ground wire connected to a post on the emergency brake bracket. However, by 1980 they also had power windows and locks, so they may also ground to the same post. Later trucks eventually added a specific grounding bar with...
  17. 75gmck25

    Question about checking current flow to the choke.

    My ‘75 K25 has a mechanical oil pressure gauge, so no oil pressure sending unit. When I converted to an electric choke I tapped into a key-on circuit that was there for the dual battery charging relay. I think some folks also use one of the wires powering their wipers. The choke does not...
  18. 75gmck25

    Fitech force fuel pump

    Please excuse, my long explanation, but I’ve been looking at EFI and gathering info on this topic for a while. The high pressure pumps used with EFI are relatively expensive, and GM chose to use in-tank units when they switched to EFI. They are designed to be fully supplied with fuel at all...
  19. 75gmck25

    Fitech force fuel pump

    If you have dual tanks, this type of FiTech pump/ surge tank is the cheapest solution. You just feed the stock mechanical pump output to the surge tank input, and then the high pressure pump feeds the EFI. Cheaper than having to buy two in-tank EFI pumps and installing a 6 port dual tank...
  20. 75gmck25

    Jimmy Tailgate Band What's it worth?

    I don’t know about the Jimmy, but for the pickups the tailgates and the center panel changed significantly from 73-80. You may have to revise your listing and figure out the exact year of your panel. The original tailgate on my ‘75 K25 had the embossed GMC logo centered on the bare tailgate...
  21. 75gmck25

    AC Vacuum Supply Adapter

    Search the Dorman catalog online for various vacuum line adapters, and then see if a local store (Autozone, etc.) carries it in stock. I also bought a hand vacuum pump and it came with about 10-12 different hose adapters. https://www.dormanproducts.com/...
  22. 75gmck25

    Need help finding short for electrical ground

    Trust me - check the main dash ground first. If missing, it will definitely affect dash indicator lights and other functions. It’s a 10 second check to make by looking up under the dash, and may save you time later.
  23. 75gmck25

    Need help finding short for electrical ground

    Ground for the dash lights is a black wire connected to a post on the top of the emergency brake pedal, which then grounds by being bolted to the body. Symptoms sound like it is not connected, or you painted something that should have been left bare metal.
  24. 75gmck25

    Removing fuel tanks

    I’ve had both tanks off my K25 to replace sending units, and if the tank is relatively empty it’s not a bad job. - Disconnect the ground wire from the frame, and loosen up (but leave the nuts on) all the bolts that attach the L brackets to the frame. Also take the screws out that hold the...
  25. 75gmck25

    Cruise Control Servo

    I think these GM cruise control servos are nearly universal across GM vehicles, so it might be easier to just find one in the junkyard that works better. Even aftermarket should work fine (they were a common dealer added option), but it might have a different shape or mounting points.

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