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  1. 75gmck25

    Temperature gauge won't move from cold

    I will have to get my wiring diagram out to verify, but I think there are only two wire connections to the gauge. That third and fourth post is just a locator pin, and it should not have power applied. try this setup - Connect a ground wire on the sending unit body only to the battery. This...
  2. 75gmck25

    Transmission Identification

    The TH-200 is a 4 speed overdrive automatic, and it works well to replace the TH350 if you don’t go too crazy on the horsepower . It can be built for high HP, but won’t handle it stock.
  3. 75gmck25

    Unable to find these relays

    They do not look like original GM relays. The GM relay for the aux battery charging in my ‘75 K25 is silver and has a smooth, rounded case. It isolates the 2nd battery when you turn off the ignition, and then reconnects it to the alternator charge wire when you start the truck. Anything...
  4. 75gmck25

    Really weird air conditioning problem

    Use A/C flush, not any other solvent, and it should be fine. It is designed to flush out the liquid completely, and any remaining residue is compatible with common A/C refrigerants and oils. Old design condensers have fairly large passages, but later on they switched to a more effective...
  5. 75gmck25

    Beginner Alternator Question

    Once again, if you buy a 94 amp GM 12si with the correct clocking, it is a direct bolt-in to replace a 63 amp 10si. It is exactly the same physical size. Depending on the year of the new alternator, the bolt on top that you tighten to keep tension on the v-belt may need to be metric to work...
  6. 75gmck25

    Beginner Alternator Question

    For everything you want to know about GM alternators and wiring, you might want to try this site. http://www.madelectrical.com/
  7. 75gmck25

    Beginner Alternator Question

    LMC has a great variety, but their prices are on the high side, and shipping adds quite a bit. For common hard parts I use Rockauto (usually cheaper) if I have time to wait, or go to the local parts store. Alternators are referenced by a universal identifier called a Lester number. The Lester...
  8. 75gmck25

    Beginner Alternator Question

    GM originally used a 10si alternator in many of these trucks, and it maxed out at 63 amps. You can substitute a 12si ( starting in ‘83) that has a standard pulley (not serpentine) and get up to 94 amps. Very easy upgrade.
  9. 75gmck25

    RETRO-Mod: Jeep intermediate steering shaft

    The jeep conversion for older trucks like my '75 (and I think trucks up to about '79) is more complicated, since the splined input on the steering box is different. For those who want to spend more and buy an off-the-shelf solution for older trucks, I installed a new -Borgeson- steering box...
  10. 75gmck25

    K-20 CV Joint

    This was the design of the CV joint on my'75 K25, and it looks different than your truck's joint. I bought the new ball and socket assembly (Rockauto, I think), along with all new sealed universal joints for the driveshaft. I also pumped a liberal amount of grease into the sliding section...
  11. 75gmck25

    Cold air at my feet and not to much in my face. Also no defrost...WTF

    It is unlikely to be the blend door, but it's also a good place to check. Blend door problems usually mean poor control of heat vs. A/C because that door is what determines whether the air flow goes through the heater core or the A/C evaporator. This is probably an issue with engine vacuum...
  12. 75gmck25

    Broken wire

    It’s probably a 14 gauge fusible link, protecting a 10 gauge wire. Cut the wire below the break and replace that section of wire with this new fusible link. https://shop.advanceautoparts.com/p/dorman-conduct-tite-14-gauge-fusible-link-wire-85620/5013070-P
  13. 75gmck25

    Is there a good spot for keyed power under the hood?

    Are you going to use a relay, or provide direct power to something? Wipers circuit provides keyed power, and so does the electric choke, but they don’t handle a lot of amperage.
  14. 75gmck25

    My wife is small and is pregnant

    It’s harder to find running boards for squarebody trucks, since the side gas tanks get in the way of the mounting brackets they use on other trucks. I have hoop steps on my truck and they are similar to these. https://www.amazon.com/dp/B008E9Z1OE/ They give you somewhere to step, but they are...
  15. 75gmck25

    Chevy Replacement Grill with 350 emblem option

    FYI - the grill on my ‘75 GMC was destroyed, so I picked up a grill from the pick and pull and it was from about a 79. Had to go back and pull the mounting brackets from the newer truck also, because the newer grill fit the opening, but didn’t match up with my original 75 brackets. Just...
  16. 75gmck25

    86 K20 Front Leaf Springs

    The Army stenciled the CUCV fender with a max speed limit, but AFAIK this is only a driver safety limit set by the Army. With proper tires they are safe at normal highway speeds. Blazer body CUCVs are relatively comfortable at normal highway speeds, but the high GVW pickups have a lower axle...
  17. 75gmck25

    86 K20 Front Leaf Springs

    My '75 K20 has the 8400 lb GVW package, with a FF rear axle, etc., and the front HD springs look the same as yours.
  18. 75gmck25

    AC Clutch Cycling Switch

    Let me try this again. My truck is a late '75, and by that time they had switched to a CCOT system. I assume your '76 is the same. Go to Rockauto.com and pick your vehicle then "Electrical Switch and Relay" then "Refrigerant Pressure Switch" There are multiple choices for the switch.
  19. 75gmck25

    Decided on a 350 engine, still deciding on stroking it out or not.

    I agree that a 96-99 Vortec 350 is the best starting point for a good midrange build, but a carburetor build may be a simpler solution. Just make sure the heads are good first (no cracks). Then pick a cam in the range of about 220-225 duration at .050. If the cam lift is too high you will...
  20. 75gmck25

    Did they mess up belts?

    Alternator belt looks fine. For the PS belt there were two OEM solutions - short belt goes around the PS pulley and the crankshaft pulley. This was the stock non-A/C belt - or there is a longer belt that goes around the PS, crankshaft and the water pump. This was usually used on A/C or HD...
  21. 75gmck25

    Rough Idle and Stalling

    16” is pretty low vacuum for an engine with a stock cam. I would have Firestone check for vacuum leaks around the entire intake, using a leak detector (propane, etc.). Also, how did you manage to switch from a Quadrajet (spreadbore) to an Edelbrock (squarebore) without changing the intake...
  22. 75gmck25

    Shakey Gauge

    Once you find the sending unit ground on the side of the frame rail, you will understand how it gets corroded and makes a bad connection. It’s fully exposed to road dirt, oil, etc. Remove the bolt, sand the frame and wire connector down to bare metal, and screw everything back down tightly...
  23. 75gmck25

    17-in rims

    AFAIK, squarebody wheels are lug centric, not hub centric ( like many newer vehicles).
  24. 75gmck25

    A/C only works when driving!?

    First check to make - with the vehicle running, put the HVAC on heat or vent. Turn the blower on high - does air come out in the right locations? This tests the blower motor and the high speed relay and the fuse for high speed. Turn the blower on next click down from high - does air come...
  25. 75gmck25

    Cooling Questions and Concerns

    If the temp is accurate, you don’t have any issues. Stock thermostat is a 195, and the engine temp may run a little above that. During a cool down cycle after a long highway run, or sitting in traffic it may spike to 210, which is also not a problem. Running at about 195-200 keeps your engine...

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