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  1. 75gmck25

    V-Belt Power Steering Pump Brackets

    GM used slightly different belt arrangements over the years, so the setup on my ‘75 is similar to yours, but not identical. Mine had the big A6 compressor, so some of the brackets were really substantial. I have two suggestions. Option 1 - slightly loosen up the bolts on all the brackets...
  2. 75gmck25

    Stock 350 with SM465 4speed

    Resurfacing should work fine, but make sure you look for cracks first.
  3. 75gmck25

    What is this thing with a bulb

    Stock light (despite its very unusual look) for the wiper switch illumination.
  4. 75gmck25

    DUAL TANKS & DIGITAL GAUGES

    Did it work fine to read the fuel level on both tanks with the original gauge cluster? There is only one fuel sending wire in the cluster plug (usually tan), and all the switching of the sending unit input between tanks is at the dash switch (older trucks), or maybe at the 6 port fuel...
  5. 75gmck25

    Let’s talk PCV systems.

    With a stock system the PCV valve is in one valve cover and the hose running to the carburetor base is pulling air through the PCV. In the other valve cover you need a to let air into the engine, which is then sucked through the crankcase to the PCV in the other valve cover. The original GM...
  6. 75gmck25

    Air conditioning controller wiring

    The high speed is controlled by the blower motor relay, so it does not go through the resistors used for the lower speeds. It goes on high speed using the blower switch, or if the temp slider is moved all the way to far cold. You can feel the slight detent as you move the temp slider to the...
  7. 75gmck25

    My steering wheel is 90 degrees off

    Go through the process in post #3 and then look at where the steering wheel points. If it points straight ahead, then all you need to do is adjust the drag link so the wheels also point straight ahead. 90 degrees off is quite a bit, but I think it would work. Clean the threads and lubricate...
  8. 75gmck25

    3rd line coming out of master cylinder?

    I did not make a serious attempt to find out if connecting hydraulic lines to your master cylinder is still “legal”. However, in some states you may have trouble during an inspection if they notice it. It just depends on the inspector. However, there are definitely now newer and better...
  9. 75gmck25

    I know I’ve asked this already but,

    Does the cluster have a black ground wire that runs from the wiring near the big plug, over to a post on the top of the emergency brake mechanism, or maybe to a ground block on the firewall? You must have the panel wiring grounded through this separate wire. It’s been a long time since I’ve...
  10. 75gmck25

    3rd line coming out of master cylinder?

    That type of trailer brake controller has been illegal for several years because any leak in that extra line could make the primary brakes ineffective. Most newer controllers either operate using a switch on the brake pedal, or they have an inertia switch with a pendulum inside that swings...
  11. 75gmck25

    carb connections...vacuum booster connection

    What do you have connected to the brake booster port on the back of the baseplate? The large threaded port on the back of the baseplate has full vacuum all the time. If it is not connected to the brake booster, or plugged completely, you will have a very big vacuum leak and the truck will run...
  12. 75gmck25

    1974 C10 Ignition switch replacement

    It may be the electric switch down low on the top of the column, or it may be a problem with the rack on the end of the lock cylinder. When you turn the key it moves a toothed “rack” on the end of the cylinder, owhich then pulls a rod up and down the column. On the other end of the rod is...
  13. 75gmck25

    Fuel tank and hose help

    Start out by getting one tank plumbed correctly, and worry about the 2nd tank later. A fuel pump with a return line usually works better because it keeps the fuel circulating, and therefore cooler and less likely to vapor lock. A fuel pump with return should be available from any food pests...
  14. 75gmck25

    1980ish K10 3 lights then 1 light on press

    On my ‘75 the rear harness ground is a white wire (I think it is for both sides) that’s grounded to the frame behind the license plate area. I don’t recall if each tail light has its own ground wire behind the housing. Also make sure the rear bulb sockets are clean and the two-pin tail light...
  15. 75gmck25

    Replaced ac evaporator now pressures are off

    I used ester and a rebuilt A6 for the initial R134a conversion, but the rebuilt A6 did not last long before self-destructing. Black granules everywhere when I pulled it all apart. The next time around I switched to a Sanden compressor and had new hoses made to fit. The Sanden compressor...
  16. 75gmck25

    Replaced ac evaporator now pressures are off

    Since several of you seem to be A/C experts, I have an additional question. - My '75 A/C was apparently a crossover year after they stopped using the TXV from '74. - The '75 evaporator has an adapter for the orifice (Rockauto site has a picture), and the adapter appears to be a brass tube...
  17. 75gmck25

    350 Engine extreme backfiring please advice

    It sounds like you may have a significant vacuum leak, since you cannot adjust idle mixture. First - get a spray can of carburetor cleaner, and spray it around the base plate and any other areas with gaskets. If there is a leak and it’s pulling in extra air, the carb cleaner will temporarily...
  18. 75gmck25

    Brass Valve Stem

    Another important point is that those appear to be high pressure valve stems, which would be correct for a K20HD. Standard valve stems are rated for a lower max tire pressure (maybe 60 psi?), but a high pressure valve stem will handle the 80 psi max of an E rated (or 10 ply) truck tire. Not...
  19. 75gmck25

    1987 V10 with 1974 engine- need TBI Help

    195 degrees is the stock thermostat for a ‘74. There is almost zero advantage from using a lower temp thermostat, since it will not help fix a marginal cooling system. With a 195 degree thermostat in the 350 crate in my ‘75 it runs about 195-200 degrees consistently, which would be a good...
  20. 75gmck25

    Hello & Seeking Restoration Info

    FYI - the drivetrain and suspension are usually straightforward to restore, and parts are readily available. Quality body shop work is expensive, and finding all the original/ correct parts for interior, trim, special options, etc. is a slow process. Lots of searching parts houses, junkyards...
  21. 75gmck25

    fuel smell

    On my ‘75 carbureted truck there is a vent line from each tank that is connected to a T fitting, and then a metal line that runs up to the engine compartment. At the engine compartment there is a rubber hose connecting the metal line to the charcoal canister. All vapor should be pulled into...
  22. 75gmck25

    Headliner

    When I removed the original sagging headliner in my ‘75 I wanted to just seal it up and glue the perforated vinyl back on. Found there was some type of foam backing on top of fiberboard, then the vinyl, and the backing for the vinyl had completely disintegrated. Cleaned all the foam off the...
  23. 75gmck25

    ac o-ring kit for '73

    Unless things have changed, just buy any kit with a variety of green o-rings and you have all you need. It’s a small bag of parts, will have plenty of each size, and won’t be that expensive.
  24. 75gmck25

    16.5 to 16 wheels 1977 Chevy C20

    My ‘75 GMC originally came with 9.50x16.5” tires and split rims, so I needed to find a better choice. I went to a junkyard and pulled 16”, 8 bolt rims ($25 each) from various GM squarebody trucks, and at that time they were easy to find. I’m sure it’s a little harder to find junked American...
  25. 75gmck25

    Drag link recommendations

    The 2026 part number is a very common part for 4WDsquarebodies. The one on my truck has been there for nearly 30 years, and I think it’s still in decent condition. What exactly is failing?

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