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  1. 75gmck25

    Convert to 350 vortec

    GM confused us all by using the Vortec name multiple times. As already mentioned, a ‘91 would be a throttle body injection (TBI) engine, and it may have the word Vortec on the valve cover. The L31 Vortec engine, with Vortec 64cc heads did not come out until about ‘96.
  2. 75gmck25

    Converting from dual saddle tanks to a single fuel tank

    Duplicate
  3. 75gmck25

    Converting from dual saddle tanks to a single fuel tank

    I’ve never looked at a short bed, so how much space do you have back behind the axle where a long bed mounts the spare tire? On a long bed you can mount a single tank in fhe spare tire area, using a Suburban tank. I think were 3 tank sizes on the Suburban, but I’m not sure the large 40 gallon...
  4. 75gmck25

    New hydraulic roller bbc break in

    I installed a GM 350/290 HP crate when I lived in San Antonio, and IIRC it was broken in with straight 30 weight and an additive they recommended. Then I switched to the high ZDDP Mobil 1 and ran that with the stock lifters for several years. Later I installed a Howard’s roller cam conversion...
  5. 75gmck25

    Fuse box

    There are extra metal tabs inside the fuse panel next to some of the fuses, and that’s type off connector (the blue, I think) can be used to plug into the panel and power accessories. The larger red connector looks more like the engine compartment (distributor, etc) or under-dash connectors.
  6. 75gmck25

    Need help fixing ac on 82 c10

    That part of the A/C control may be a little different from year to year, so it usually needs to match your truck year (82?). It also has a part number on one side, printed in black. I’m not sure if a single year may have had different part number for this part.
  7. 75gmck25

    Heads and manifolds

    The GM crate will have a mild cam with duration about 195/202 degrees @ .050. It also has low compression heads (maybe 8.2) that don’t flow that well. Typical upgrades - Good dual plane intake (Edelbrock performer, performer rpm, or equivalent is least expensive) - advance the base timing to...
  8. 75gmck25

    Horn blares when my ac high low fan switch comes on

    Door switch wiring is white, and the switches ground the wiring when the door is open. Orange wires are the constant power feed to the interior lights, cigarette lighter, etc. Horn wiring runs to a horn relay under the dash. IIRC, it is not plugged into the fuse panel, but is a separate relay...
  9. 75gmck25

    How do I test mechanical fuel pump

    My ‘75 350 has a three port fuel pump with a return to the tanks. I have replaced the fuel pump twice (one leaked) over the years, and found the Autozone pumps worked fine. Some Autozone stores do not stock the correct 3 line pump, so I had to get it from one of their bigger regional stores...
  10. 75gmck25

    Stock 400 small bock with bigger cam

    Stock heads are low compression and low flow, so they don’t play well with an aggressive duration cam. The 350/290 hp GM crate is a good example, where they use a 222/222 @ .050 cam to get the engine HP up from the cam used in the base 350/250 HP crate. It works, but loses low end torque, and...
  11. 75gmck25

    Temp Gauge Is Not Working

    The temp gauge circuit is very simple. - 12 volts applied to one gauge terminal when ignition is on - other gauge terminal connects through cluster wiring to the green sending unit wire in the engine compartment, which is clipped on to the sending unit terminal - sending unit is a resistor...
  12. 75gmck25

    Transmission tunnel heat shield

    Also check to see if your cab bushings are collapsed. When I replaced my cab bushings I was initially really confused because the cab got so much quieter. Finally figured out that with the old bushings and two people in the cab, the cab body was sitting right on top of the transmission and...
  13. 75gmck25

    New hydraulic roller bbc break in

    15w50 or 20w50 are not the same as straight 50 weight oil, so I would not expect that weight to cause any issues. However, I would probably just stick with something like 10w30 or 10w40 full synthetic.
  14. 75gmck25

    What at these metal components on gauge cluster?

    Gauge with the missing metal tab is the voltmeter, and IIRC it only needs power and ground. All the illumination light bulbs are the same, and then there are also bulbs for left and right turn signal, brake warning light, and the high beam indicator. I replaced all of mine with dimmable...
  15. 75gmck25

    1985 C-30 454 Vaccuum line to AC/Heater Control

    That is called hard/rigid vacuum line, and it is sold in two sizes. You can easily splice it with short sections of rubber line. This is one example https://www.dormanproducts.com/p-6924-47417.aspx . They used to stock it along with the other Dorman products, but I haven’t looked for it...
  16. 75gmck25

    Vacuum operated heater air conditioner controls

    The small diameter line goes through firewall, across the back of the dash, and then provides the vacuum source for the A/C controls. As you move the dash selector switch, it switches vacuum to the four (?) vacuum motors that operate the HVAC. If you look at an original GM HVAC diagram it will...
  17. 75gmck25

    Quadrajet adjustment mixture adjustment screws

    Double D mixture adjustment tool works on the original mixture screws, or many carburetor parts stores will sell you new mixture screws with a standard flat tip screw head.
  18. 75gmck25

    Fuel delivery troubleshooting

    On a dual tank truck there are multiple short rubber fuel hoses. They are old, and may have cracks or holes in them. Modern fuel with ethanol makes them deteriorate even faster. The mechanical fuel pump pulls/draws fuel from the tanks, so any leaking hose can cause it to draw air instead of...
  19. 75gmck25

    76 Orange paint code

    There is a small metal dash panel right above your knees under the steering wheel, and it’s only held on with about 4 screws. Remove that panel, which should be less faded than the rest of the truck, and take it in to be color matched. I’m not sure if a paint store can match it to a 1976 GM...
  20. 75gmck25

    Timing marks

    No, they really suck! Went through two that had a faulty tachometer (read 1400 rpm when the truck was at 800 rpm), and then they charged me a restocking fee when I finally returned the last one. If it does not work correctly, their only fix is to give you another one. I then bought an Innova...
  21. 75gmck25

    Dash Pad Help

    Dashes Direct makes a quality product, and several vendors sell them. It’s an oversized shipping item, so when you compare prices from different sources, make sure you include shipping.
  22. 75gmck25

    Dual tank solenoid valve

    Ref post #35 - I’m not sure how the multi-wire solenoid and dash switch works inside. It is motorized inside, and stays in whatever position you leave it (constant power not needed). I’ve also seen dash switches that tell you to push and hold the switch to change tanks. It sounds like it...
  23. 75gmck25

    Dual tank solenoid valve

    It sounds like you have a single terminal solenoid. These will default to the main tank with no power, and to the opposite tank when 12 volts are applied. The “main” tank varies over the years. For my ‘75 ( and up through ??) the passenger side was main, and/or the only tank for a single...
  24. 75gmck25

    Settling on timing

    If someone used a TDC tool in the past, the two extra marks make sense. When using a TDC tool you turn the engine one way until it stoops, mark the balancer, and then turn it the opposite direction until it stops, and mark again. Halfway between the marks is TDC...
  25. 75gmck25

    ProFlo 4 O2 Location

    Instructions for my Innovate LC-1 AFR sensor tell you to install the bung between a 9:00 and 3:00 position in the exhaust pipe. Not sure why the Pro-Flo diagram is a little different, but it does give you better access to remove/install the sensor when it is angled to one side.

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