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  1. 75gmck25

    Oil Leak Into Cab

    ‘86 has an electric sending unit, so no oil leak into the cab is possible. Up until about ‘76 they used a mechanical oil pressure gauge with an oil line into the cab. Did someone swap your gauge cluster?
  2. 75gmck25

    Question about converting to a roller cam

    I made the conversion on my Gen 1 SBC, so I’m not sure how similar it is for the 454. I bought a Howard’s conversion cam and lifters, and both are completely different than any stock roller setup. I then bought a Cloyes timing cover with an adjustable cam button. I could have used a...
  3. 75gmck25

    no power on ac wire to compressor

    Power runs from the dash switch, to the thermostatic switch (low temp probe that goes into the evaporator), then through the discharge pressure cutout switch (which you apparently found) to the compressor. - If the pressure is too low in the system, the low pressure switch turns it off. This...
  4. 75gmck25

    Another exhaust options thread - what should I do?

    Glass pack or straight through is just a type of low restriction muffler. It will usually have a straight through perforated pipe down the middle (you can look right through it) for low restriction, and there will be fiberglass packing around the pipe. The perforations and packing are...
  5. 75gmck25

    Hey...what's the big idea..??

    The original Quadrajet on my ‘75 is one of the older models, and due to some of its issues I didn’t even try to rebuild it. However, I’m now using a Quadrajet pulled from an ‘85 C30, and based on the numbers it is a 1980 or later version. It’s probably one of the last models with no electric...
  6. 75gmck25

    Vacuum diagram

    Cruise control uses a vacuum servo to pull the throttle, and it's usually mounted on the driver's side fender well. There is a cable that runs from there to the carburetor and it connects in parallel with the cable from the accelerator. On my '75 the back of the cruise control servo points...
  7. 75gmck25

    Vacuum diagram

    With a diesel, don’t you need to have a vacuum pump? Or am I getting confused (again)?
  8. 75gmck25

    Another exhaust options thread - what should I do?

    I used a 2 1/4” dual kit from Summit, an h-pipe, and Magnaflow mufflers. It has a low performance sound at idle and low rpm, and then gets throatier and louder if you hit the throttle hard. It’s never real loud, but you can definitely tell there is a V8 behind it.
  9. 75gmck25

    Heat box swap

    My K25 came from family in North Dakota, and I’m now in Virginia. I have never suffered from a lack of heat in the truck. What temp thermostat do you use? I have a 195 degree thermostat (stock for my engine) and it usually keeps the engine at about 190 in the winter. I don’t block off the...
  10. 75gmck25

    Factory smoke

    Hooked cables up backwards on my ‘75 (why did GM factory use black cables for both?), and all it did was burn the fusible link that is connected to the junction on the firewall next to the brake booster. It all worked fine once I replaced the link and corrected the cable polarity. Mine was...
  11. 75gmck25

    temp sensor

    The hole in the block of that ‘81 engine should be 1/2”, and sensors come in 3/8” and 1/2” threads. Looks like an adapter bushing was used to make a 3/8” sensor work. Many aftermarket mechanical gauge kits include the adapter bushing.
  12. 75gmck25

    Just advice please

    I have done many hillbilly repairs, but it was to my vehicle and I understood the trade-offs. Usually it was an interim fix until I could do the job right. However, I don’t want to take on someone else’s hillbilly repair because I don’t know how many shortcuts they took, or where the risks are.
  13. 75gmck25

    Just advice please

    When you estimate the value of the of the squarebody, you should be very pessimistic - it is a truck with an engine that runs badly, and therefore it needs a new engine. If it was simple and easy to fix, why hasn’t the PO already fixed it? If it turns out better than that, and the fix is...
  14. 75gmck25

    Temp gauge says overheating but the truck is 195°

    Exactly which sensor did you buy? The sensor resistance profile changed over the years, and usually the one the parts guy pulls up for older trucks is not correct. It took me a while to find one that worked well with my ‘75, and it’s got the correct 1/2” threads. The TS6T has the nailhead...
  15. 75gmck25

    Valve cover bolts won't stay snug.

    Stamped steel covers should have small steel load spreaders, which are also usually arched a little to create a spring effect as you tighten them down. That should help. Rubber gaskets with metal reinforcement usually work well, but they are quite expensive. I used them with my aluminum valve...
  16. 75gmck25

    Charcoal canister delete?

    My ‘75 truck originally had a dedicated purge line port on the Quadrajet, and I assume it worked. However, I now have a Quadrajet on there from an ‘85 C30. I first just T’d the purge line into the PCV line, but that means I have introduced more air all the time. Now, for my FYI for those who...
  17. 75gmck25

    Gauge cluster

    The clusters changed slightly over the years, so you need to know the year of the replacement cluster to get a good idea of whether it will work. As it evolved, GM also changed the pinouts on that big connector, so even if it fits it might not make the right connections. For example, my ‘75...
  18. 75gmck25

    Stock radio mounting

    The two shafts are mounted into the metal dash. There is also a factory rear metal support/strap that extends down to the bottom of the metal dash, secured with a screw on the lower edge of the dash. Most radios have a threaded bolt sticking out the back of the radio, specifically for a...
  19. 75gmck25

    ‘83 K5/ SBC 350 Swap/ new/old oil sending unit differences/dash gauge/Autometer gauge?

    If you look on eBay you will see many choices, mostly marketed for the oil line on a Turbo. Just make sure it has the right threads. They used to stock the Dorman brand in most parts stores, but it’s not there lately. The Dorman version is 3 parts, using a brass tube to connect down to the...
  20. 75gmck25

    ‘83 K5/ SBC 350 Swap/ new/old oil sending unit differences/dash gauge/Autometer gauge?

    You can put a T in the port/line where it connects near the distributor, but now you have multiple connections that can leak. I would make sure the senders are well supported, so vibration doesn’t cause anything to loosen up.
  21. 75gmck25

    Speedometer refuses to work. Any help is appreciated

    You should be able use a drill to spin the transmission end, and it will make the speedometer read. If that works, then it’s the transmission connection you need to work on.
  22. 75gmck25

    Stuck O2 Sensor

    Start out with PB blaster or penetrating oil. Did you buy an O2 sensor wrench? They are designed to fit over the sensor and give you max mechanical advantage to get it off. You should be able to find one at NAPA or other parts store, or get it quick from Amazon.
  23. 75gmck25

    Squarebody chassis swap build help: Were there any exterior differences between 81-87, 2wd/4wd and weight classes (c10, k30, etc)

    I have read in other posts that there are frame differences in the one ton trucks. I know the rear shock mounts are definitely different on a one ton, and others have said the frame is thicker in certain areas. However, I couldn't put my finger on any specific documents to verify.
  24. 75gmck25

    Definitive interchangeable parts thread 73-87(91) (non-drivetrain)

    The logo on the early tailgates was centered, so the GMC embossed on my ‘75 is in the center of the sheetmetal. Later on they switched to putting the GMC logo on one side, and Chevrolet on the opposite side. Not sure when that change started.
  25. 75gmck25

    Rim compatibility

    If you just need a spare, and don’t plan to use it in a tire rotation, you can also use a 16” wheel and tire. 16” 8 lug rims are extremely common in the junkyard, and you just need to use a tire with the same diameter for a spare. My truck originally had 16.5” split rims (hard to find a tire...

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