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  1. 75gmck25

    heater fan - always on?

    There was a heater shutoff valve on some vehicles, but I’ve never figured out which ones. I found a two port vacuum-operated heater bypass valve several years ago. With vacuum applied, the heater water flow went from the engine to the valve, made a u-turn and went right back to the radiator...
  2. 75gmck25

    Heater / Defroster Options

    What capability do you want to add? Basic defrost and heat usually works well in all the trucks if the system is working properly. Then I think some non-A/C trucks have a dash vent option to give you better warm weather venting. However, I’ve never actually looked at a non-A/C truck with dash...
  3. 75gmck25

    Sending unit 4 tubes

    Depending on the year of the truck and the canister they used, there are also some vacuum lines and switches for the tank vent system. Basically they need to allow it to vent the tank by connecting to the carburetor, but only under certain conditions. If the venting was constant it would be...
  4. 75gmck25

    74 C10 rear end interchange

    All of the 1/2 ton square-body rear axles should bolt right in, but the driveshaft yoke may be different. Not a problem if you have a local place that can change it if necessary.
  5. 75gmck25

    Larger steel wheels

    Wheel Vintiques has a lot of classic wheels. I’d just take a look through what they offer.
  6. 75gmck25

    Temp gauge not reading

    Bottom line - based on Rockauto site, the TS76 sending unit or equivalent is probably the one you need, unless your cluster is '79 or older. With the older cluster, try the TS6 or TS6T. One aspect of my '75 is that it only shows 1/4, 1/2, 3/4 scale in the gauge, so I have no idea what exact...
  7. 75gmck25

    Debugging my AC problems

    If your compressor is working, and if you can find a shop that will recharge the system for a reasonable price, most other parts are relatively affordable to fix. Is the system still R12, or has or been converted to R134a? Many shops got rid of their R12 equipment and refrigerant years ago...
  8. 75gmck25

    1985 305 keeps dying after a few seconds

    Disconnect and plug the fuel line so you have no gas coming into the carburetor. Then start it up and see if it smooths out and runs until the float bowl is empty. If it seems to idle and run fine, then it’s definitely a problem with the float, needle/seat, etc.
  9. 75gmck25

    Temp gauge not reading

    Temperature sending unit resistance and the matching gauge has changed over the years on a squarebody. For example, if you have an '82 gauge and a '75 sending unit, it will not read correctly because the resistance of the sending unit does not match the gauge. However, it will usually still...
  10. 75gmck25

    Truck cranks and starts and dies immediately

    The wiring colors at your starter are not original. - red wires appear correct, but there should be a fusible link in the small red wire (maybe it’s just not in the picture). This is constant power to the fuse block. - yellow wire should be on the R terminal if you have points, and it’s only...
  11. 75gmck25

    Firewall mounted terminals

    Main power (large gauge red cable) runs from the battery positive to the starter. The starter terminal then has a 10 gauge wire that runs from there up to that distribution block on the firewall. From there you have a power wire running over to the fuse panel, and on most trucks a wire with a...
  12. 75gmck25

    Speedo working but Odometer not working

    The mechanism for the odometer is pretty simple, but relies several internal parts moving reliably. My guess is that a tab broke off internally, and the only good fix is a new speedometer. The oil pressure gauge is mechanical, but usually works fine. You can get a tach conversion kit that...
  13. 75gmck25

    Engine install

    I installed mine with the exhaust manifolds already bolted on. It worked fine, but it was a PIA to jockey it around to line up and reach the motor mount bolts. In hind sight, I would bolt the exhaust manifolds on after installation.
  14. 75gmck25

    Black wire connected to indicator lamp

    It may be the black cluster ground wire. On older trucks it was grounded to a post on the top of the emergency brake, but I think newer trucks have some type of ground bus up above the pedals. I assume that the ground bus has posts or spade terminals and the ground wire(s) go on them...
  15. 75gmck25

    Bench seatback foam from LMC - anyone else installed it?

    I ordered the 73-80 bench seam foam and tan seat cover from LMC, and today I started stripping down the seatback. When I unboxed the foam I found that the foam for the seatback was three pieces - the main cushion and an add-on piece for each end. Called LMC and they said that the added...
  16. 75gmck25

    Hello from Virginia

    I tried to get regular Virginia inspection on my '75 K25. The first thing he did was look under the hood (visual emissions equipment inspection) and say "it doesn't look like it's all original", and one park light also looks like it has a crack, so it won't pass regular inspection. I think he...
  17. 75gmck25

    TH350 transmission

    Checking it with a tach is the best start. These trucks echo like tin cans, so noise from the engine is amplified. When I replaced cab bushings I also found that my cab was resting down on the transfer case, so all the drivetrain noise was transmitted directly up to the cab. My K25 has about...
  18. 75gmck25

    8' bed question

    IIRC, the only unique bed feature of my ‘75 Camper Special was two cutouts in the front panel. The ElimiPitch camper brackets bolt to the back of the cab, and stick through those holes in the front panel and into the bed. Shock absorbers then bolt to the brackets and to the camper. The...
  19. 75gmck25

    Get a Clean Look and Strong Support with Luverne® 6" O-Mega II™ Side Bars I Free Shipping

    Am I missing something? According to the search function on their site, this vendor does not make a running board or any other product for a squarebody.
  20. 75gmck25

    Old school garage door opener remote

    If you are able to swap in a few pieces from a newer vehicle there may be a simpler solution. Ford used to offer a universal door remote (at least in 2000) that was built in to the visor, and it could operate three devices. I think GM put in their similar system in using buttons in the...
  21. 75gmck25

    K5 almost killed me brakes to the floor

    If the linkage is all intact, my best (somewhat educated) guess is that the piston seal inside the master cylinder has torn or otherwise failed. However, the pedal will usually still return up, so check the external mechanical linkage and the rod first.
  22. 75gmck25

    Did this K20 come factory with catalytic converter?

    If you search this site and any hotrodders site you will find many folks who are trying to figure out if they just bought a 305 or 350 SBC. Unless the inspector is willing to crawl into the back of the engine and inspect the pad with the engine casting number, there is nobody I know who could...
  23. 75gmck25

    Removing instrument panel - dealing with the oil pressure line

    They sell deodorizer and spray for cleaning and getting rid of the smell from cat urine, but I don’t know if it’s also effective for mice. If you’ve ever rented or bought a house where cats peed on things, you know why you need special cleaners.
  24. 75gmck25

    Debugging my AC problems

    The vacuum module on the controls diverts vacuum to the right vacuum motors so you get air flow to defrost, heat, vent, A/C. The A/C compressor will work without vacuum to the controls, but the default air flow will be about 1/2 to floor and 1/2 to the defroster. Original refrigerant was R12...
  25. 75gmck25

    Did this K20 come factory with catalytic converter?

    You need to find a more experienced emissions station, and one that will actually look up and show you the data instead of using words like “always”. Most younger (and older) guys have no real knowledge what specific emissions was installed on a nearly 40 year old truck, so having them rely on...

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