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  1. 75gmck25

    Alternator amps

    Good point - the current 10si (or its wiring) is bad, and the simplest fix might be just to use a direct replacement. Alternator testers at the parts store seem to be unreliable. I think they just check for continuity and maybe some resistance values to see if they are within spec. They don't...
  2. 75gmck25

    Alternator amps

    The CS130 and equivalent are excellent, but are a slightly different form-factor and wiring than the old 10si. Not a big job to adapt, but some folks don’t want to modify anything electric. My choice - The 94 Amp 12si is a drop-in replacement for the old 10si, and the 12si is sold with either...
  3. 75gmck25

    87' a/c brackets

    Old R4 compressors are not great. Look for a kit to adapt a Sanden or Seltec and get the brackets they use.
  4. 75gmck25

    New memeber old mechanic 73 chevy 350

    Welcome! Check the rear end to see if it’s a 14 bolt FF, which are used on the high GVW C20’s. Brake work on a FF is harder because you have to pull the axles to get the drums off or replace a wheel cylinder, so it gets ignored for many years. You might just have a really bad wheel cylinder...
  5. 75gmck25

    Vortec Head Timing With Progression Ignition

    Vacuum advance is not related to performance tuning, since as soon as you open the throttle the vacuum will drop and the vacuum advance goes away. You can mostly plug the lone and ignore it when first setting base and mechanical timing. Vacuum advance is there to improve the burn at steady...
  6. 75gmck25

    1980 C10 Cruise Control Switch 407437

    Most common brand is probably Rostra, but Iditit and Dakota Digital also have them. Problem is that they are about $400 and up. GM cruise control was nearly identical across multiple model lines, so start looking at both GM car and trucks for the parts you need. Lots more cruise control...
  7. 75gmck25

    75 Chevy SWB 4x4 adding a saddle fuel tank on driver's side

    It’s a relatively easy mod once you get the parts. The fuel filler hose is not very flexible, so it has to match the filler setup (hole in bed side versus door). You need a 6 port or 3 port fuel solenoid, and matching wiring and dash switch. Original setup used sections of metal line running...
  8. 75gmck25

    Intermittent cruise control

    I would start by checking the wires for chafing or breaks. The controller relies on a reliable signal from the speed sensor on speedometer cable (or in a '91 maybe it comes from the ECU), and it might be dropping out the speed signal. The other place to check is all the vacuum connections...
  9. 75gmck25

    Power loss with aggressive acceleration

    What type of carburetor is on the 6 cylinder? When a 4 barrel has this type of symptom you would usually check to make sure the secondaries are working and properly kicking in, but I thought the 6 cylinder used a two barrel carburetor. The other items to check is the float level and the fuel...
  10. 75gmck25

    1991 Suburban 3/4 ton: TBI to Holley Sniper conversion - stupid, or worth it?

    To some degree, a Holley Sniper on the stock TBI heads and cam is like putting lipstick on a pig. Lots of shiny new parts, but probably not that much difference in power with stock cam and heads. To get more out of the sniper you will need more cam, but not one that goes beyond the compression...
  11. 75gmck25

    Bed liner paint.

    I’ve seen a few factory trucks (don’t recall the brand) where they used a bed liner-looking paint to protect the rocker panels. Not sure what it was called, and I haven’t seen it used in quite a while.
  12. 75gmck25

    Loose timing chain replacement

    Also, if you get the idea to upgrade to a double roller chain, be ready for some more work. In most cases the extra width of the double chain hits the oil gallery bosses on the upper front of the block before the timing set is fully seated. It’s relatively easy to grind the bosses down for...
  13. 75gmck25

    What’s the best way to fix/clean up this wiring problem?

    First figure out what all those wires are going to, so you understand what you have. Also, is this an auxiliary battery? Those large battery cables look pretty wimpy for a squarebody stock cable. The instructions for many aftermarket accessories state that you must make the power connections...
  14. 75gmck25

    Instrument panel light question

    My ‘75 did not have a light to tell you the parking brake was on, but it does have a wire going to the proportioning valve, which turns on the light in the dash if there is a brake line failure. This light works by grounding the wire to turn on the dash light. Newer trucks did have parking...
  15. 75gmck25

    Instrument panel light question

    Taylor, I think the picture you posted is of a newer truck than the 74/75 era. For the older trucks I think it was just a single wire connected to that bolt, and in later years they added the bus/fitting for multiple grounds (like in your picture). I only found the missing instrument panel...
  16. 75gmck25

    Instrument panel light question

    I have a spare instrument panel out of my '75 with gauges and a clock, so I looked at the wiring. I believe the correct ground is an 18 gauge black wire that comes out of the big multi-plug and runs over to ground on the pedal mechanism. It comes from terminal #150, which is at the far end...
  17. 75gmck25

    Instrument panel light question

    It is almost certain to be a ground issue. When a ground is bad, devices “find” other paths to ground, and lights go on and off. Did you securely attach the instrument panel ground wire ( its a separate black wire, not the big multi-wire plug) to the post on the parking brake mechanism? If you...
  18. 75gmck25

    Fuel pump

    It could be a weak pump, but usually they just leak. However, I would also check the spring and Quadrajet fuel filter to make sure it is correctly installed. It’s an easy mistake to make. Also check the float level and the needle to make sure you aren’t just emptying the float bowl and running...
  19. 75gmck25

    Fuse panel

    It was probably wired differently on a the '89, but my '75 Camper Special has the factory 2nd battery option and it uses a relay mounted on the driver's side inside the fender. Its a relatively small relay, since it only has to handle the charge output from the alternator. - From the power...
  20. 75gmck25

    Can anyone tell me what this is??

    I installed a couple aftermarket cruise controls, and they both had two magnets you epoxied to the driveshaft. Then you mounted a sensor on the body and it stuck out near the driveshaft (1/4”?). Magnets spinning around near the sensor were used to measure road speed. However, the device shown...
  21. 75gmck25

    Headers and O2 sensor

    If you have a heated sensor it can be farther down the pipe, away from the exhaust manifold, since it does not rely on engine heat to come to operating temperature. Simple two wire sensor needs to be as close as possible to the collector so it heats up quickly. All should be no more than...
  22. 75gmck25

    Fuel leak?

    A couple of years ago I had a fuel pump that was shooting a small squirt of fuel out the side/top through a crack. It was going right onto the exhaust manifold and pipe, and then immediately evaporating from the heat. Constant gas smell, but nothing running onto the ground.
  23. 75gmck25

    Skool me on timing w/o timing tab

    SBC timing tabs may be at the 2 o’clock position, or 12 o’clock (the ones I have seen look more like a vertical tube than a tab), and think there may be one other possibility. To get started: - Pull all the plugs, mark the #1 plug position on the distributor body (white paint, nail polish...
  24. 75gmck25

    Trailer wiring on a 77 K5? How do I do that?

    This diagram shows the difference between the wiring standards. So you need to know what the trailer has. No wonder things get wired wrong. https://www.loveyourrv.com/wp-content/uploads/2022/09/Trailer-Wiring-Diagrams.jpg
  25. 75gmck25

    Trailer wiring on a 77 K5? How do I do that?

    https://www.etrailer.com/Trailer-Wiring/CURT/C57672.html?feed=npn You need to use the Curt adapter in post #4 above to connect the wiring for a 4 pin adapter, which should have these colors. White - ground (will be grounded to the truck body) Yellow - left turn/brake Green - right turn/brake...

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