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  1. 75gmck25

    Electrical Issue No Power When Keyed On

    GM fusible links are usually one of two designs. - Early trucks (like my ‘75) just have a piece of wiring in the loom that looks too fat and/or is a different color. If there are markings, they are usually very hard to see. I have this type of fusible link at my starter for the 10 gauge charge...
  2. 75gmck25

    Power steering pump bracket for heads without accessory holes.

    I’m not sure I understand what is not working. Do your heads have the accessory holes in the front of the passenger side head? Stock setup on my ‘75 has a large bracket bolted to the front of the head, with a hole in the end that is pointed toward the frame rail. The end of the PS bracket in...
  3. 75gmck25

    Where do I fine starter cable and other wires?

    The positive cable on my ‘75 is simply a cable with the side post battery fitting on one end, and a lug for the starter terminal on the other. It routes down toward the fuel pump and then along the oil pan flange to the starter. It’s nothing complicated. RockAuto show the positive cable for...
  4. 75gmck25

    83 K20 for sale.

    If you want to attract more of the hot rod crew you might provide some specs on those aluminum heads. Stock low compression heads on these engines really limit performance potential, but most folks don’t want to start out by swapping to heads with higher compression and a valve train that...
  5. 75gmck25

    Goodwrench crate engine smoking from passenger side exhaust

    What type of carburetor do you have? On a Quadrajet or Edelbrock the secondaries open based on air flow, so nothing happens to move the secondary flaps when you actuate the throttle with the engine off.
  6. 75gmck25

    Goodwrench crate engine smoking from passenger side exhaust

    I had one wet plug and a tick from that side of the engine. Turned out the rocker arm polylock had loosened enough to let the pushrod pop out of the recess. Basically one dead cylinder.
  7. 75gmck25

    Does my 79 have a fuel filter in unit?

    With a 3 port fuel pump and 3 port sending units you just put a T fitting in to connect both vent lines to the metal line running up to the vapor canister. Each tank’s supply and return lines connect to the 6 port Pollack valve and when you switch to a tank it switches both return and supply to...
  8. 75gmck25

    Posi Traction

    I’m not sure that changing axle ratio and going to a slip rear end is the best performance upgrade to start with, and the minor difference with a 3.42 is definitely not worth the trouble. Since you have an overdrive transmission, if you go that route I would use a 3.73 or even a 4.10 rear...
  9. 75gmck25

    2wd fuse panel in 4wd

    The 4WD Lok light listed in the ‘77 brochure really interests me. I would love to know what type of sensor they used to determine the shifter position on the NP203 and turn on the light. Since my NP203 is unconverted, I just leave it in Hi position (AWD) all the time. I put it in the...
  10. 75gmck25

    2wd fuse panel in 4wd

    BLUF - in that timeframe I think the fuse panels for 2WD and 4WD were identical. In ‘79 they were still using only the NP203 and NP205, and I don’t think there was any 4WD light in the dash. I know my ‘75 K25 has no dash light for 4WD.
  11. 75gmck25

    Oil leak

    Original steel valve covers have relatively flexible flanges and there are supposed to be small spreader bars at each bolt hole to make it seal better. However, gaskets leak, spreader bars get lost, and bolts get tightened too far and bend the valve cover flange. - check the holes in the...
  12. 75gmck25

    Fuel sending unit help

    On my truck the third port has a T connection to the other tank and then one line runs to the charcoal canister under the hood.
  13. 75gmck25

    Fuel only gets to engine when tank is out of the vehicle

    Did you also replace or work on the fuel filters, or run the engine with the air cleaner off? Sediment/junk can get under the needle and let the engine flood, but it will usually run fine at higher rpm because it can burn the fuel and not flood out. You can get similar symptoms if you suck...
  14. 75gmck25

    SBC dual exhaust redux

    There is also a company in Texas that sells new 2WD crossmembers that get good reviews. I’ve always been disappointed that they don’t have anything similar for the 4WD trucks, since it doesn’t seem like it would...
  15. 75gmck25

    1978 k10 radio patch panel

    I made my own patch panel using some sheet metal I got from Home Depot. It took trial and error to get the holes right, but I bought a new dash gauge bezel off eBay and used that as a template. It was time consuming, but not really that difficult. Once you get the dash bezel back in place...
  16. 75gmck25

    Playing with hookers today. 10 out of 10!

    Many stock O2 sensors are unheated, so they need exhaust heat to operate correctly. These must be close to the exhaust manifold. If you are using an aftermarket (5 wire?) sensor, like the ones used with many wide-band AFR gauges, they are heated sensors that would work even if at the end of...
  17. 75gmck25

    replacing power steering pump

    Not sure I understand the question. The PS fluid feed line from pump to steering gear is under pressure and it has threaded fittings, but the return line just has worm clamps because it has very little pressure in it. Big difference.
  18. 75gmck25

    Fuel gauge won't read below 1/2 tank, electrical or mechanical issue?

    I’m using Autozone sending units in my ‘75 GMC and they seem to work fine with the stock gauge. However, they are not very linear as the fuel goes down in the tank. I have learned that I can go from 1/4 tank to out of gas in a very short time. However, I’ve never measured the resistance as...
  19. 75gmck25

    Playing with hookers today. 10 out of 10!

    Is this a stock SBC, and which manifolds did you use? Hooker shows two parts number 8525 and 8527, and it seems like the 8525 has the standard rectangular port for an SBC head. However, the text says it’s for engine swaps, so that confuses me.
  20. 75gmck25

    I need help with gauge wiring

    If you want to make consistent money with automotive repairs, continue down the path of understanding the wiring, especially when you get to cars that have computers. There are many great mechanics who can fix anything except a wiring problem. It usually requires only patience and good...
  21. 75gmck25

    What do I have...Dana 44 or GM 10 Bolt

    My ‘75 GMC K25 has what is called a Dana 44 HD, 4.10 ratio front axle, but I’m not sure what makes it an HD. It may just be whatever is changed at the hub area to allow for the 8 lug wheels.
  22. 75gmck25

    A request for assistance with Fuel transfer valve, switch, and fuel gauge

    On the older carbureted trucks you only have a single mechanical fuel pump. If the tanks use a 3 port sending unit (supply, return, vent) with a return line you need to switch both return and fuel supply lines, so it requires the 6 port valve.
  23. 75gmck25

    A request for assistance with Fuel transfer valve, switch, and fuel gauge

    I put new sending units in both tanks of my ‘75 GMC K25 a few years ago and I got them from Autozone. Closest store did not stock them so I had to drive about 20 miles to a different store. I have the original 6 port solenoid with only a single power terminal, so my wiring is basically stock...
  24. 75gmck25

    erratic fuel gauge

    I put new 3 port sending units in my ‘75 GMC K25 a few years ago and I got them from Autozone. I think they are a little inaccurate at the low end of the scale, but that may be because my old tanks don’t have any baffles. I still have the old 6 port solenoid, so my wiring is simpler than...
  25. 75gmck25

    replacing power steering pump

    After you replace it, also make sure you get all the air out of the system. The GM procedure is to lift the front tires off the ground using jack stands, and then with the engine running turn the steering wheel full lock-to-lock ten times. Then check fluid level. It seems like overkill, but...

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