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  1. 75gmck25

    1979 Dash Pad Replacement

    My ‘75 GMC has a buckskin color interior, but the dash is a little darker buckskin/tan than the rest of the interior (almost a brown). I think you may have the same color. I bought my buckskin dash pad from Jegs and it was made by Dashes Direct. LMC has one priced about the same, but if their...
  2. 75gmck25

    84 K10 full exhaust replacement

    If you want to keep using a catalytic converter, just get an aftermarket high flow cat. They are much better flowing than the original catalytic converters from the 70's and 80's.
  3. 75gmck25

    3” header back exhaust pipe kit for 2wd?

    Are you going to run full dual 3”? That is serious overkill for a 350. Spend money on things that will get you more bang for your buck.
  4. 75gmck25

    Heat and AC

    Why don't you try downloading this repair manual and taking a look through the PDF document. This is part of the reference library on this site, and they also have wiring diagrams and other information...
  5. 75gmck25

    Replacing K20 fuel tank

    I deopped my tanks a few years ago to replace the sending units. It was a PiA, but with a nearly empty tank I could put a 2x8 under it and raise and lower it with a floor jack. Once you get it up enough it can’t shift left or right and fall off the jack because it’s kind of crammed in there...
  6. 75gmck25

    Oil Pressure and Temp

    Also check the gauge panel ground. It’s a black wire grounded to a post on the emergency brake mechanism. Gauge panel wiring uses a large, wide plug that has all the wiring connectors. If PO was troubleshooting up under the dash he may have moved the wiring around and partially disconnected...
  7. 75gmck25

    FUEL TANK CAPACITY 1982 K10 4x4

    The older tanks are not baffled, so how low on fuel you can go may depend on the angle of the truck and whether you are turning a corner. I was running low on one tank and turned a corner that also went up hill and the truck suddenly quit. Switched tanks and it started right up. That fuel can...
  8. 75gmck25

    Manifold and ported vacuum

    Your description, and the use of the terms fast idle and normal idle, are confusing. Now that I think of it, let's simplify your setup and answer some questions. Do you like how your base and mechanical timing setup performs? - Disconnect and plug the vacuum advance line to the carburetor -...
  9. 75gmck25

    Dual tank install

    The wiring and switching valves changed over the years, so your best bet is to find a donor truck of a similar year and swap everything except the rubber hoses (those you should replace). If they left everything in place there should be metal hard lines that cross under the cab between tanks...
  10. 75gmck25

    Blend Door Panel

    The blend door is inside the plenum, behind the glove box. Do you mean the door in the kick panel for the max cooling / recirculate function?.
  11. 75gmck25

    Manifold and ported vacuum

    I have aluminum heads and I run manifold vacuum with 15 degrees base timing and 20 degrees mechanical (in by 2000 rpm). My vacuum advance adds 17 degrees. In general, aluminum heads tolerate more timing without pinging because they dissipate heat better. I want to make sure of your timing...
  12. 75gmck25

    Stock Cold air intake performance upgrades

    You have the tall air filter, which flows plenty for any SBC. Most trucks (like mine) have the standard height filter. Dual snorkel air cleaners are available in aftermarket and factory reproduction versions. I’ve seen them every year from vendors at Carlisle. However, I’m not sure the...
  13. 75gmck25

    84 K10 full exhaust replacement

    If you ever swap to aftermarket heads, watch out for brands that use a 1/2” higher exhaust port, and different spacing on the spark plugs. It’s a fairly common change (not sure why), but it makes stock manifolds harder to fit, and there is usually less space for spark plug boots. Some brands...
  14. 75gmck25

    14 bolt brake cleanup

    When I had my ‘75 14 bolt FF rehabbed by a local shop many years ago (2003?), the shop manager said he had to buy multiple brake parts kits to get all the right matching parts. He was really proud of getting it to all look and work like original. The only minor issue is that if I leave the...
  15. 75gmck25

    AC Troubleshooting 1976 GMC C15

    My condenser is right up against the radiator, with only some thinstrips of rubber cushioning between them. I am using the stock 7 blade mechanical fan and severe duty fan clutch, and air flow is not an issue.
  16. 75gmck25

    AC Troubleshooting 1976 GMC C15

    Where is your orifice valve located? On my ‘75 the metal tube coming out of the bottom of the evaporator has a fitting large enough to hold the orifice valve , but it looks like yours would not be large enough.
  17. 75gmck25

    which bench seat is best? 75? 80? 81?

    I installed new seat foam and velour upholstery on my ‘75 a couple of months ago. Found one broken spring on the drivers side and had to fix it by welding a barrel connector over the two broken ends. It explains why the old seat always felt like it tilted the driver to the left. Seat cushion...
  18. 75gmck25

    84 K10 full exhaust replacement

    On my ‘75 the NP203 transfer case support has lots of exhaust space on one side and much more limited on the other. Had to carefully position 2 1/4” pipe so it would not bang against the case support or rest on the transfer case. One company in Texas now sells a W-shaped support that provides...
  19. 75gmck25

    Source for rear AC fittings?

    When I had my new A/C hoses built they found that GM used a larger diameter hose fitting than normal for the evaporator connection, probably because the orifice tube fits in there. The A/C shop just took two fittings of the right size, cut them apart and braised them back together to make an...
  20. 75gmck25

    82 C10 EFI Conversion project

    Is there some reason you want to use electric fans? I have the OEM 7 blade metal fan, severe duty fan clutch, aluminum 3 row radiator, high flow water pump, and stock fan shroud and I have never come anywhere close to overheating. I think I could leave my truck idling in the driveway with...
  21. 75gmck25

    NP203 leaking. Replace or fix?

    I know just enough about 203s to be dangerous, so my point was to just be sure what you’re buying. I am not an authority. It may be possible to reclock the NP203, but I’ve never seen anyone mention it except in the context of making a range doubler. Spline count may also be nothing to worry...
  22. 75gmck25

    NP203 leaking. Replace or fix?

    Just make sure you are buying a used NP203 configured for a squarebody GM truck and with your same transmission. All three major manufacturers used the NP203, and there are variations for spline count, left or right drop, etc.
  23. 75gmck25

    Booster shocks?

    A kit like this is usually easy to install, but more designed to stop sag than to give a lift. https://www.airliftcompany.com/products/air-springs/loadlifter-5000
  24. 75gmck25

    Source for rear AC fittings?

    AFAIK, '74 was about the last year they used an expansion valve system on the squarebody trucks. My '75 has an orifice tube/holder for a fixed orifice that is built in to the lower hard pipe on the evaporator. The original system used a GM white fixed orifice, but based on recommendations I...
  25. 75gmck25

    Am I Crazy? Lincoln Drive Train Swap

    The Ford 460 has cubic inches, but it’s a Mom and Pop cruiser engine without much potential. It never came in a factory high performance version, and swapping in Cobrajet 429 parts would get expensive real quick.

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