1966 c20

[Hantke]

So I drover her home today, DEFINITELY not ready for the highway! I get a loud slapping in 3rd gear on occasion and 4th when I'm revving. Presumable something loose under the hood. On the bright side, with a full tank of mid grade gas she starts with zero issues and runs ALOT smoother. On the not so bright side autozone tried to sell me the wrong lock 3 times so now it's sitting without a driver side lock on my street. I'll be moving it back to the shop tomorrow to complete some work on it. I also found that I can't seem to go much faster than 45 MPH (at least that's what the speedo showed and my tail driver told me that as well). The speedo decided to go hay wire on me about 1 mile down the road anyways, so let's add that to the "needs fixing" section.

I think I've decided this truck will be getting the 350 V8 (haven't decided about the auto transmission that comes with it) after the rebuild. This 250 is awesome and all, but I need to go highway speeds.



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[GMCDAC]

Not trying to talk you out of the 350 at all but the 250 should easily push that truck highway speed. Something else is up causing that 45 mph top end.

The 230 in my '55 GMC will run down the highway 75 mph no problem but I keep it 60-65. I need to get a tach someday. The slapping sounds like something in the drive train.

Just guessing that the speedometer cable probably needs cleaned and lubricated. When they get sticky they kinda wind up and release causing a very erratic reading. Truck looks great, thanks for the updates.

DAC

[Hantke]

I figured it was the 4.11 gears with the SM420 originally paired with a 327 V8 then converted to a smaller 250 causing the low top end speed, I might get the 350 and rebuild it in my spare time just for the experience, plus I'll have a spare engine (if I can get the highway speeds out of the 250 there will be no point in replacing it). Here around me the fastest highway is 65, and most are only 55. I'll look into the the speedo cable tomorrow while I replace the door look with the correct (hopefully Napa pulls through, auto zone is failing) cylinders. And the Tach needs to be fixed. Also realized my fuel gauge is stuck at half full no matter how much or little is in there. The other major thing is that the brakes pull hard left when I hit them. I'll also have to update the steering as it's extremely loose. (Probably just a U-joint or something). My though with the slapping was that it might be the old choke cable that is currently just sitting on the brake fluid reservoir.
I would much prefer not to drop the 350 in (I'd love a 327 to convert it back to original) because that's a complete cookie cutter truck if I do. Though if I go that far I will just go on ahead and put a canopy on it so when I start contracting I have a work truck. It would be a good excuse to buy a GMC pickup to use as my own personal vehicle! Though I would instead prefer to get a panel truck to make my work vehicle out of.

On the bright side, I did decide on the final colors for the truck, I'm thinking of a dark forest green with a white cab and fawn interior (all white and orange W/ white cab were close seconds).


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[bigblockv6]

Would that be the GM code 505 Woodland Green which is correct for that era?

[Hantke]

I'm not sure, in thinking for now I will use rustoleum high gloss enamel and see how I like it, and then in a few years down the road when I can afford all the tools I'll do a proper base-clear paint job on the truck. But for now the enamel will be great because it's easily fixable from any scratches or anything and being my only truck, it's gonna get scratched at some point at work.


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[Hantke]

The GM Woodland green is nice, but I'm not sure k want to go quite that color compared to the forest green, but we'll see as time goes on.
Woodland green:


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Forest green:


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The forest green is still wet, it dried darker.

And don't mind all the extra spray marks on the cardboard, I was trying different things like direct on cardboard, double coating it, one coat on primer, etc. most of it was off to the side but that's where I set the ash tray for a color test.


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[David R Leifheit]

Originally Posted by Hantke

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I figured it was the 4.11 gears with the SM420 originally paired with a 327 V8 then converted to a smaller 250 causing the low top end speed, I might get the 350 and rebuild it in my spare time just for the experience, plus I'll have a spare engine (if I can get the highway speeds out of the 250 there will be no point in replacing it).

Just curious, how did you determine it was a 327 originally?
Does the VIN start with CS, CE, or CT?
Or is it a C2### ... (C 2 number, number, number?)
I find two different sites for VIN decoding for 1966.
The 250, according to what I can find, was the "new" engine for 1966.

Unless you have an overdrive transmission, top gear is usually 1:1. At which point engine RPMs determine the top speed (when deciding between engines with the same transmission/axles).
From my motors manual the 250 horsepower is 150 at 4200 while the 327 horsepower is 185 at 4400 rpm. So both motors pull their "best" horsepower pretty close to the same place, rpm wise. So at "peak" the 327 might move the truck a little faster, but the 250 will still get close. Running empty you shouldn't see any difference at all.

Basically speaking the 250 will move the truck at highway speeds.

The advantage to the 250 in a truck over the 327 is the 250 develops its torque (235) at 1600 RPMs while the 327 (305) at 2000 rpm, meaning that the 250 develops its torque lower, getting a load moving and up to speed "faster" than the 327 will.

That is with all things (engine condition) being equal/new.

I went looking for the rear axle combinations available for 1966, but the manuals I have are a bit lacking for Chevrolet. The Motors Manual doesn't list, that I could see, the ratios available per year/motor.

*If* your rear end is 4.11:1, then both engines will move it at lower speeds than if it were 3.08:1

[FetchMeAPepsi]

Man too bad you're not closer to me. I'd let you play around with my paint gun and see how it looks. The Blonde is forced to fly to Portland pretty often but my air hose won't stretch that far.

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[Hantke]

I was told that the original motor was a 327, and that the gearing was 4.11 as well, I haven't had the time to verify what they said. the original owners son pulled the 327 for his own use and a 250 I6 was put in in its place, and a lot of the wiring and the jerry-rigged A/C hose setup agrees with that entirely.

Maybe I'm running into another issue that I haven't identified yet, perhaps the fuel filter is too restrictive or something else is causing the engine to not accelerate to the proper RPM's. Now knowing that I can keep the 250 I6 I see no reason to replace the engine. I know the exhaust is basically Ghetto, it's half way welded together and has gaps in it, I believe one of the manifolds also has a leak, but I have yet to remove them as when I do I would like to sand them down / clean them up and repaint them. It would be nice to do everything at once so I don't have to worry about removing it again later and replacing the gaskets again.


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[Hantke]

Originally Posted by FetchMeAPepsi

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Man too bad you're not closer to me. I'd let you play around with my paint gun and see how it looks. The Blonde is forced to fly to Portland pretty often but my air hose won't stretch that far.

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I've got a nice Matco professional paint gun that I will use for the final coat, I just don't have an air compressor any more! I used to paint heavy equipment for CAT, granted that was all enamel, my mentor taught me some base clear techniques to.


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