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  1. 75gmck25

    Replacing The Quadrajet

    I think Edelbrock also sells an adapter so that you install a 1406 or an AVS2 carburetor on a stock spread bore intake.
  2. 75gmck25

    Pollack Tank Selector with AN Fittings

    On most trucks the primary tank sending unit wire is tan (pink when faded), and the aux tank wire is tan / with white stripe. The dash switches between the two wires to change the gauge reading between tanks.
  3. 75gmck25

    What is this thang on my 84' Silverado?

    They are fusible links, and they are sized four wire gauge numbers higher than the wire they protect. For example, to protect a 10 gauge wire you use a 14 gauge fusible link. Older ones are marked with wire gauge numbers (10, 12, etc.) and newer ones have metric marking (2.0mm, 3.0mm).
  4. 75gmck25

    Pollack Valve Wire

    Is your ‘85 truck a mixture of old and new, because the single wire Pollak tank valve was only used on earlier trucks. Your ‘85 should have a six wire valve. Also, the picture seems to be of the fuel sending unit, not a tank switching valve.
  5. 75gmck25

    Flipping bbc intake gasket leaks

    Not sure about a BBC, but on an SBC those on the end are blind holes, so it is possible to have the bolt bottom out before it’s snugged the intake down fully. I had to swap in 1/4” shorter bolts when I went from the SBC stock cast iron intake to an aluminum intake because the flange was...
  6. 75gmck25

    LS or 454

    Do you plan to do all the work yourself, or pay someone else? The 454 was a common option in the squarebody trucks. If you are patient about checking junkyards and reading online articles, you can find all you need to know about the 454 conversion, and you may even keep it on a reasonable...
  7. 75gmck25

    Hide engine wiring

    GM used plastic split loom at the factory, and it works well to hide all the wiring colors and keep wires together. They also sell clips/retainers that clip around the loom and have a nub that pops into a hole (maybe 1/4”) drilled in sheet metal, so it holds the loom in place. It’s not very...
  8. 75gmck25

    defrost not working

    All the doors for plenum air flow use vacuum actuators. Only the heater blend door is cable operated by the heat slider control. Engine vacuum is provided by a line that runs from the engine compartment, through the firewall and to the dash control. Moving the control switches engine vacuum...
  9. 75gmck25

    Which cam for a carbed 350 vortec?

    Another important item to check - is this really a ‘96 and up Vortec roller engine? Get the casting numbers off the heads, and also check for the roller block spider in the lifter valley. GM put the Vortec logo on many products, even a 6 cylinder engine, so make sure you have a genuine Vortec...
  10. 75gmck25

    Which cam for a carbed 350 vortec?

    Vortec heads have good flow and compression, so they respond well to a more agressive cam . The original cams are quite moderate (196/206 @ .050, etc.), so for a street vehicle it usually works well to upgrade to a cam that has up about 214-218 @ .050 duration. This duration used to be called...
  11. 75gmck25

    Ignition switch rod came loose

    When I took mine apart I found that the rack had cracked and was flexing, and the rod had way too much play for the switch to operate correctly. The rack is made of cheap pot metal and not very durable. Rack and gear mechanism is cheap to buy, but time consuming to replace because it’s deep in...
  12. 75gmck25

    Bench Seat Identification

    I may be confused because my ‘75 does not have the original seat. The trim pieces may have come with higher trim level packages, not on later seats.
  13. 75gmck25

    Bench Seat Identification

    The plastic side trim pieces tell me it’s from a much later truck than your ‘75. Early trucks (at least through the early 80’s) had a visible metal bracket connecting the seat cushion to the back, and it did not have a plastic trim covering.
  14. 75gmck25

    1980 Scottsdale C30 3 fuel doors but just 1 tank? adding a tank or 2 and in tank fuel pumps

    Based on several other performance sites I read, the Edelbrock Performer RPM dual plane is a good mid-range choice for most street builds. It’s a medium rise (I think) and provides a few more HP than the cheaper base Edelbrock Performer. They also sell an Air Gap version to keep the mixture...
  15. 75gmck25

    Tie Rod Ends Interfere with Wheel Weights

    Instead of a shop that only does what the machine says, look for a tire shop that caters to performance cars or off-road tires, and have them do the balancing. Some wide/large performance tires are very hard to balance, and the owners may also want it to appear absolutely show-car quality from...
  16. 75gmck25

    Are these modern carburetors a big improvement?

    One way to get carburetor working a little better is to install a wideband AFR gauge and use it to monitor the mixture. Then adjust and set it to keep it closer to the best AFR, which will vary based on the operating conditions at the time. For example, idle AFR might work best at near 14.7...
  17. 75gmck25

    Are these modern carburetors a big improvement?

    Cylinder wear issues have been significantly reduced because most modern EFI systems keep AFR within very close limits. Modern carburetors are now usually better at keeping the mixture correct, but they still rely mostly on mechanical linkage and vacuum. They can often been tuned to have a...
  18. 75gmck25

    Where can I find this battery tray?

    Another option - My ‘75 Camper Special has a factory auxiliary battery tray on the driver’s side in the engine compartment. IIRC, it’s the same tray as the main battery, but the support under it is a little different. Camper Special wiring included a relay that allowed the alternator to...
  19. 75gmck25

    Vacuum lines for hvac system

    FYI - Dorman sells the GM hard plastic vacuum line in small rolls. You can join/splice hard line using short pieces of rubber vacuum line. The original hard vacuum line should have a colored stripe that matches the colors in the repair manual. This makes it easier for figure out which line...
  20. 75gmck25

    Converting from dual saddle tanks to a single fuel tank

    Unless you just like a challenge, or this is part of a bigger EFI conversion project, using the original dual saddle tanks, with a mechanical pump, and bringing them back to life is the simplest and cheapest way to go. Nearly all the parts are available from either junkyard or as new parts, and...
  21. 75gmck25

    Vacuum lines for hvac system

    This is a picture of the hvac on my ‘75 GMC. - The flat round canister up next to the a/c plenum is the vacuum reservoir for the hvac controls, and it has a rubber vacuum line running from it over (down low) to manifold vacuum. - There is also a small diameter hard plastic vacuum line coming...
  22. 75gmck25

    1979 k20 blower motor

    As Ricko1966 explained, the lower speeds go through the resistor pack and the fuse in the fuse panel, but high speed uses the blower relay, and it’s powered through a separate fuse and power feed. You need to troubleshoot high speed and lower speeds separately. To troubleshoot high speed you...
  23. 75gmck25

    Timing at 25 degrees advanced - harmonic balancer slipped?

    It’s going to be hard if you can’t verify TDC. There are are at least two different timing pointers used on the SBC (12 o’clock and 2 o’clock), and the original pointer is tack welded to the timing cover. Someone may have swapped the timing cover or the balancer and now they don’t match. I’ve...
  24. 75gmck25

    Convert to 350 vortec

    Pull the valve covers and get the casting numbers off the heads. That is key info you need . If they turn out to be L31 Vortec heads, then pull the intake manifold off and also verify whether it has a roller cam spider.
  25. 75gmck25

    Heater blower motor battery drain

    On an A/C truck there is a wire with a 30 amp inline fuse, running from the junction block near the brake booster over to the blower motor relay on the plenum. When the blower is on high, it’s powered through that fuse, not the fuse in the fuse box. I don’t know if a non-A/C truck has that...

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