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  1. 75gmck25

    Intake Manifold Install

    I put the engine at TDC and then pulled my distributor cap off to ensure it was pointing at #1 (left all the wires on the cap). Then I used a small paint brush to put a white line on the distributor to show exactly where the rotor was pointing. Makes it all much simpler when you reinstall...
  2. 75gmck25

    What zero lash on the lifter rod should feel like?

    I have also seen suggestions that jiggling the rod up and down is easier to feel the zero point. When you go up and down it’s a simple go/no go choice (does it move). When you spin the rod you need to calibrate the “feel” of your fingertips to know how hard it is to rotate. YMMV.
  3. 75gmck25

    Am I missing brackets?

    The original compressors are generally not very reliable. You might look for a kit to convert to a new Sanden. I know they have kits to convert the big boat anchor A6 compressor, so I assume you can also convert from the smaller compressor. I used a Sanden on my ‘75, but found a local shop...
  4. 75gmck25

    Did speakers come default or was that an added option

    On a ‘77 (like the OP) I don’t think they had the option yet for dash corner speakers. My ‘75 definitely does not have cutouts for them.
  5. 75gmck25

    Charcoal Canister Line Routing Question

    I have a similar situation with my ‘75 GMC, which originally had a Quadrajet with a dedicated port for the canister venting. I don’t know how that port worked (e.g., when it pulled vacuum), but the documentation is clear that it was for the vacuum canister. With my newer carb I installed a T in...
  6. 75gmck25

    1977 k20 build

    Stock gearing for a K20 should be 4.10. Are you sure the transfer case is really in High? Shifter alignment can be way off, so maybe it’s actually in low range. 4.56 was also an option, but I think it was used mostly in the K30s. TH350 was stock in many of these trucks and it will hold up...
  7. 75gmck25

    Help me understand 5.0 disparities

    The Ford 302 is in the same family as the 221/260/289. The 260 and 289 were used in the Falcon Sprint and the Mustang, and there were several performance variations, including the high performance 289 used by Shelby in the Cobra two-seater and the Shelby 350 Mustang. That engine family got...
  8. 75gmck25

    Turn signal not working left side

    Most likely to be a bad ground at the tail light. Take both rear housings out, locate the ground wires, and sand the body to bare metal where it screws in. Then ensure the screw tighten up. There is also a larger gauge white ground wire for the rear wiring harness, usually grounded to the...
  9. 75gmck25

    Dual gas tank set-up idea.

    For your year truck, that should be the right valve. The issue I have is that my ‘75 has an older 6 port valve that is no longer available. If I swap in a newer design 6 port valve I have to do quite a bit of rewiring, and I probably need a new dash switch. However, so far my old valve is...
  10. 75gmck25

    Dual gas tank set-up idea.

    The stock dual tank setup is not that complicated. However, it uses a lot of rubber hoses, which have deteriorated from ethanol fuel, and the older 6 port valves are no longer sold anywhere. I still have a working older 6 port valve (with a single power lead), and I’m lucky that it works...
  11. 75gmck25

    Dual gas tank set-up idea.

    Makes we wonder how they did a frame off “restoration” but didn’t get the fuel right. Your scheme might work, but why jury-rig and re-invent the wheel. - Get one tank working properly with your pump and a return line and make sure it draws down the tank to near empty. Pump should be mounted...
  12. 75gmck25

    Carb not getting fuel

    I usually just dump a capful of fuel into the carburetor throat, using the plastic cap from my tire foam or any other one handy. That provides enough fuel to get it to fire, and once you have some rpm the fuel pump will push fuel into the float bowl. In summer weather it should fire right up.
  13. 75gmck25

    Did speakers come default or was that an added option

    AFAIK, no trucks had a radio stock (always an option), but all had the holes punched in the top of the dash for speakers.
  14. 75gmck25

    Where does negative battery cable ground wire attach?

    The battery ground wire on my ‘75 is bolted to a hole in the top of the alternator bracket. Easy to reach and definitely well grounded to the engine. I also have a ground strap from the top of the frame near the fuel pump over to the block, and a ground from the back passenger side corner of...
  15. 75gmck25

    Suburban 56" Leaf Spring Options

    I’m not a Suburban owner, but I think Any 56” squarebody spring should fit. You might look for aftermarket springs that are listed as soft-ride. However, you might also need to then add an overload spring for those times you fill the suburban up with 8 people and their luggage.
  16. 75gmck25

    Blue Print or GM Performance

    Intake is covered in splashed oil on the inside when running, so no point getting too excited about getting it squeaky clean. Just check that the pluggs are sealed tight. The BP350CTCD engine spec says it uses H8002K heads, which are a 64cc head with performance equivalent to a Vortec head...
  17. 75gmck25

    Vacuum for 1979 GMC

    You can probably use either vacuum port, and it originally used the timed port. However, I find it best to time and tune with distributor vacuum disconnected and plugged, and then reconnect to manifold vacuum when I’m done. This bumps up idle timing a little and makes it run smoother.
  18. 75gmck25

    Fuel Pump?

    I found that my rubber lines had exterior cracks and were breaking down inside, and it seemed that the pump might be sucking air instead of fuel. I replaced all the rubber lines with newer ones that are more ethanol resistant. There are a lot of short rubber lines on a squarebody with dual...
  19. 75gmck25

    240 vs 260 temperature gauge

    Simple answer - maybe. What is the source for the new gauge? GM changed the gauges over the years, and each year or range of years uses a slightly different sending unit. For example, my ‘75 sending unit would be very unlikely to provide an accurate reading of temp on your truck. Take a...
  20. 75gmck25

    Sniper Coolant Temperature Probe Location?

    Stock location for the dash gauge temp sensor is in the drivers side head where you found it, and it should be a green wire. It all looks correct. Some older iron heads had a 3/8” tapped hole, but newer 350 engines are usually 1/2”. My aftermarket aluminum heads have a 3/8” hole. There is...
  21. 75gmck25

    Vac Advance - Yes or No?

    Vacuum advance is mainly there to get better gas mileage at cruise on the highway. It usually has minimal effect on acceleration and general performance. You are giving up cruising speed gas mileage, but that’s your choice.
  22. 75gmck25

    Temp gauge problem

    It runs through a protective sleeve where it’s next to the exhaust manifold and the sending units in the head. If the sleeve is missing it may burn through the insulation and ground on the manifold.
  23. 75gmck25

    79 c20 tire size help

    245/75R16, load range E are very close to the original diameter and load rating for a 8400 lb and up GVW truck. It’s also common to use 235/85R16E, which are slightly taller. 185/75R16 would be very small for a 3/4 ton SRW truck.
  24. 75gmck25

    Fuse blows when fan speed on high

    On my ‘75 the high fan speed uses a separate 30 amp fuse. It is in a wire running across the firewall from the power junction near the brake booster over to the blower relay on the A/C plenum. This is the stock setup. Maybe a newer truck is wired differently. The original barrel-style fuse...
  25. 75gmck25

    Blows Hot Air When Off?

    Based on my experience, it’s hard to get relatively cool fresh air. It just seems to pick up heat regardless of what you try to fix. I tried a vacuum-operated heater bypass valve - stopped water flow and helped cool it down a little, but water in heater core was still warm. Also remove the...

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