"New" 1981 GMC

[Axle]

Picked up a new square on the weekend, a barn find 1981 GMC 1500. Dash trim says High Sierra but that is questionable, as with every truck I come across, the SPID is missing. Hopefully I'll get to a dealer sooner rather than later to see if I can still get a list of RPO codes for it. (anybody here work for a dealer willing to run the vin? Canada truck if it makes a difference to what info is available on either side of the border)

Previous owner (GM Tech, 2nd owner, got it in 1983) added cruise control, and a/c from an '84/'85 truck at some point in its earlier life. Wheels from some other timeframe. Its rolled the odo over a couple times. 305 dualjet th350c and 12 bolt rear axle. Sheet metal is in great shape, as the only winters it has seen was the first few years of its life.

It has been painted sometime in the 90's and debadged. Interior needs a bunch/a lot of TLC and all the hoses need replacing. Thing still runs good, and even with the massive vacuum leaks it was well behaved and starts up quickly with zero smoke. Sips the gasoline compared to my '83, so plans for now are to run it as is until my right foot gets the itch. =-)

Interior smells like a barn... becuase it was housed in a barn for at least 10 years. For someone who has never named a vehicle (other than the standard curse words thrown at them when warranted), it has coined itself 'the farm truck', fitting for where it spent its life.

Some questions that you guys more than likely can answer;
-What year (year range) is the A/C from? Did that compressor get introduced in '84 or '85? I'm inclined to suspect 1985 since the instrumet bezel is an '85 if the a/c specific stuff came from the same donor truck.

-What is that contraption in the air filter housing? Some sort of backfire supressor? For all the cars and trucks I've looked at in the yards, I have never, ever, seen an inner metal mesh filter. Does it require periodic cleaning/spray down with carb cleaner? Whatever it is, it seems like it is crimped to the air cleaner housing, which doesn't lend itself to easy maintanence.

On to the pics, barn pic later as those are on my now self destructed other computer.

Alex.

[Axle]

Some more. And the cassette it came with, Meat Loaf Bat out of Hell
Another question, years range of the HVAC controller?

Alex.

[Just call me Sean]

My '83 has that style compressor, as did my '86. My '87 has it but the clutch is clocked different. The '86 had that air cleaner thing, don't know what it's for. The '83 has a cheap chrome one and the '87 is fuel injected so it's different.

[Axle]

If I find out anything about that mesh filter I'll post it up.
Any idea if the hvac controller is setup the same on all three of your trucks? I don't like not knowing what year parts I need to order ahead of time should I need them. =-)

Alex.

[Just call me Sean]

The inside controls? Those all look to be the same. The underhood stuff has some differences. I like to use the AutoZone app to cross reference parts.

[Jonboy]

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[jetmech85]

The A/C compressor and hoses look to be from the '81-'82 era. I have several '81 and up parts trucks and they all had the short R-4 compressor if they were a small block. The condensor had a hose going to the drivers side and cross over to the passenger side by routing over the fan shroud. My '85 has the hose routing to the condenser across the alternator bracket. All the later fan shrouds still have the un-used bosses for the hose clamps. If you upgrade the condenser to the ones that are available now the hose will go to the passenger side. The compressor clutch/pulley is also the type used in '81-'82. I believe the pulley is a little closer to the compressor housing also. Your pics don't show it but an '85 bezel would not have had an opening for a dash mounted wiper switch. I have had few trucks with that type of air cleaner and not sure what it's purpose is. Those trucks were all 3/4 tons. The wheels look like 90's era sport trucks. Hope this helps you.

[Keith Seymore]

As far as determining option content - you have two options but they both cost money:

1) Because your truck appears to have been built and/or sold in Canada you can contact GM of Canada Vintage Vehicle Services. Send them your VIN and $60 and they will tell you the actual option content for your specific vehicle.

Link: http://www.vintagevehicleservices.com/

2) Because your truck is an '81 you can also access the information through the GM Heritage Center archives.

Send them your VIN and $50 and the can give you the specific option content and pricing for your specific vehicle.

Link: http://www.gmmediaarchive.com/?page=3

It will look something like this:



Lastly, here is a free download of all the generic option content and descriptions for the '81 model year: https://www.gmheritagecenter.com/doc...olet-Truck.pdf

K

[beamn7]

The mesh screen is supposed to act as a muffler / spark arrestor. GM listed it as a "deflector" Most of us (including yours truly) removed them....http://67-72chevytrucks.com/vboard/s...d.php?t=209687

[Axle]

Thanks for the info guys. Something new around the corner to learn everyday.

The charchol content mentioned in the link about air filters stands out. Wonder what the criteria behind it being there or not was, and how many year(s) they where used. (short term = problematic or ineffective, and something to get rid of asap).

Jonboy, its an Alpine 7163. Definatly old school, all mechanical selector switches.

Alex.

[Axle]

If all else fails, look for a patent.
http://www.freepatentsonline.com/3747303.html
1973 patent. The original patent referenced is from 1968.

A ring of activated carbon particles for adsorbing and desorbing hydrocarbon vapors rising from a fuel reservoir in a carburetor of an internal combustion engine. The ring has an elevated portion above a base portion. Both portions extend between an air inlet side and an air outlet side and between top and bottom surfaces for securing and sealing the ring across the air path through an air cleaner. The elevated portion has passages that conduct air for the normal operation of the engine from the air inlet side of the ring to the air outlet side. Hydrocarbon vapors adjacent the outlet side from the carburetor are adsorbed by the carbon in the base and elevated portions before rising to the level of the passages. With the engine running, the vapors previously adsorbed are desorbed by air flowing from the inlet to the outlet side of the air cleaner into the carburetor.

And in reference to the other thread where someone mentioned the carbon element was not as tall as the air filter, apparently it only needs to go "up so high" to be effective.

For adsorbing the heavier-than-air fuel vapors as they rise from the carburator the carbon ring has a base portion and an elevated portion thereabove. The elevated portion has passages therethrough to permit air required for the normal operation of the engine to flow substantially unrestricted from the air inlet port of the air cleaner to the air outlet. The base and elevated portions cooperate to adsorb the hydrocarbon vapors before they rise to the level of the passages.

Alex.

[beamn7]

Learn something new everyday! Thanks for posting that Alex, good info.