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  1. 75gmck25

    Fusible links ?

    There are two fuses like that on a ‘74 and they are part of the shunt/circuit for the ammeter. GM used the wiring loom itself as a shunt for the ammeter in the dash so they didn’t have to run full alternator current up to the dash. However, to for an ammeter shunt to work properly you must...
  2. 75gmck25

    Master cylinder ran dry

    As already mentioned, do not get carried away with “mashing” on the brake pedal and pushing it down too far to bleed air. The MC has been on there a long time and the piston seal inside has probably built up a ridge where the pedal stops moving the piston during normal braking. If you push the...
  3. 75gmck25

    Firewall circuit breaker

    On my camper special there is a wire from that junction over to a relay on the fender. That relay is used to charge the aux battery and/or power the camper. The camper relay connects the aux battery to the alternator when the truck is running, but then isolates the aux battery when you turn...
  4. 75gmck25

    1982 c10 interior right turn signal

    Did you reconnect the blank instrument panel ground wire to the grounding bus or post? If it’s not connected it causes multiple light issues when the panel “finds”another ground path.
  5. 75gmck25

    1986 K10 vacuum and emissions routing help needed

    What does your ECM control, since you don’t have fuel injection (electrical connection on carburetor?)? And exactly what carburetor are you using? With no EGR and no EFE, I think you could simplify the emissions equipment and hoses a lot, but I’m not clear on what has already been removed.
  6. 75gmck25

    1985 scotsdale stepside duel fuel tank

    Stock fuel tanks were the same left and right for for all carbureted squarebody trucks (EFI trucks got a baffled tank). LMC truck, RockAuto and many other places sell them. I assume you have 16 gallon tanks on a step side, since there isn’t enough space for the 20 gallon tanks...
  7. 75gmck25

    SBC 350 Possible issues with Carb?

    A stock mechanical pump should be within Edelbrock specs, so I would verify the pressure and then go from there. I have never purchased a pressure regulator, so I don’t have any recommendation. The link provided in the previous post is for a gauge, not a pressure regulator. I used a similar...
  8. 75gmck25

    SBC 350 Possible issues with Carb?

    Edelbrock’s are sensitive to fuel pressure (keep to about 5psi or lower) and float level. My guess is that one of those is off and it’s throwing in too much fuel and screwing up your mixture.
  9. 75gmck25

    What are these?

    Sounds like the PO may have planned to install cable-operated exhaust cutouts.
  10. 75gmck25

    Hvac blend door question...

    Unless you are stuck on that vendor, they are sold by multiple vendors, including LMC. I think you can even get them from RockAuto.
  11. 75gmck25

    Engine Bay Wiring Identification

    My ‘75 camper special has a relay in about the same location, and it’s for the camper wiring and 2nd battery. For my truck it is activated by an ignition-on wire from the fuse box, and was designed to provide isolation of the aux battery to power the camper when the engine is not running.. I’m...
  12. 75gmck25

    A/C Compressor, again.

    I am no A/C expert, but PAG oil is recommended and used in many OEM A/C systems because of its excellent lubricating properties. It may not be the optimum choice for retrofit of an old system, but it should work fine if the system is cleaned and evacuated properly. Ester is usually better if...
  13. 75gmck25

    1978 Toyota SR5- One for Dad

    Do a little research on the 4 cylinder engines of that vintage (or a little later), looking for issues with the timing chain guides. There is one version of the Toyota 4 cylinder engine (I think it’s the 22R) that used plastic timing chain guides, and they got eventually got brittle and broke...
  14. 75gmck25

    defrost not working

    Seems like a high price for a very simple clip, but at least you get free shipping. LMC has the same part for $5.95, but then you have to add shipping.
  15. 75gmck25

    Plug Gap - Suggested or Altered with HEI?

    GM confused things back the day by initially recommending a gap as wide as .060, which was apparently intended to get a better mixture/burn for emissions. However, they quickly realized their mistake, and since then it’s been .035-.045 for most HEI engines.
  16. 75gmck25

    Heads and manifolds

    Keith, I just took a closer look at your last message and noticed you list the engine size as 327. Is that correct? The 327 was a great engine in its day, but never a factory option for the squarebody trucks. The reason is ask is that the 327 came in multiple versions, and some are quite a...
  17. 75gmck25

    Should I go POSI???

    I do remember the days of driving a 428 Ford Torino GT with traction-lok. Plenty of torque to spin both rear tires and swing sideways at just about any speed. It was a learning experience.
  18. 75gmck25

    Tuning chart Edelbrock 1400

    If you are seeing the timing retard as rpm goes up, and then advance again, there may be an internal problem with the distributor. It’s probably worth your time to borrow another light and see if you get the same readings. I prefer to manifold vacuum, but you should be able to make minor...
  19. 75gmck25

    Tuning chart Edelbrock 1400

    if you want to start at the beginning for your tuning I would try a few things first. - buy a dialback timing light with a tachometer. I am using one from Innova, but there are several other brands. - use a piston stop (home-made or purchased) and verify TDC for #1. Move the timing pointer or...
  20. 75gmck25

    Tuning chart Edelbrock 1400

    As already mentioned, make sure your timing is correct first. With the Edelbrock 1400 series of carburetors a part throttle bog may be due to two problems. Either the step-up springs are rated too low (e.g., 5" springs when 7" or 8" rating would be better), or incorrect settings for the...
  21. 75gmck25

    Radiator for my 83 GMC 305 with a/c recommendations

    The copper/brass vs. aluminum cooling capability comparison can get very complicated. Copper/brass itself conducts heat better than aluminum, but the tin used in manufacturing does not conduct as well. Then you have to look at the number of rows, thickness of material, durability, , etc. As...
  22. 75gmck25

    Fuel sender replacement?

    Mine uses 3 port sending units and I got them from Autozone. Only the larger store carried them for our trucks (I think it’s is also a regional distribution point), so I had to drive a few miles, but otherwise no issue.
  23. 75gmck25

    Wiring gremlin - Nothing works unless trans is in reverse

    Large battery cable runs down to the large lug on the starter. From that lug you have two wires with fusible links. #1 runs up the back of the engine through a metal tube, along the valve cover top, and connects to the bat terminal on the alternator. This is the battery charge wire. #2 runs up...
  24. 75gmck25

    4L80E Information Thread

    Anyone one have any info/suggestion about using a junkyard 4L80 and transfer case (which one?) to replace a TH350 and NP203 in my '75 GMC? Would it work and what are the most likely problems/challenges (in addition to the driveshaft replacements)?\\ Thanks.
  25. 75gmck25

    Radiator for my 83 GMC 305 with a/c recommendations

    Go to Rockauto.com and look at the standard radiator sizes for your truck. Then compare the dimensions to the one you have and decide what part number you are looking for. For example, my '75 GMC K25 with A/C uses the CU161 (28-1/4 x 17-1/4 x 1-1/4) which is the original size for a 3 row...

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