Help locating GVWR, etc for 79 K20

[KIILew]

Blink:

This doesn't really address the discussion your having with Captkaos, but I thought I would present some additional info here...

For 1976, the K10 pickup was offered with just one GVWR: 6,200 lbs. The 1979 K20 you were considering, however, (or for that matter, a 1976 K20) could have had any one of three GVWR’s: 6,800; 7,500; or 8,400 lbs. Here are some figures you might consider, compiled from the 1976 and 1979 Chevy Truck Data Books (and some 1976 and 1979 brochures, as well). To keep things simple, I have determined the curb weights for only the basic vehicles described (and accounting for any necessary hardware to achieve the noted GVWR’s); additional optional and aftermarket equipment would increase these weights, and therefore reduce the payloads relative to what I have shown below. Still, the figures below give some idea of the differing capabilities of these GVWR packages.


Specifications for 1976 K10 @ 6,200 lb GVW w/350 4bbl V8/SM465 and Tubeless Tires --

Frame Section Modulus: 3.92

Front Spring Capacity: 1,850 lbs each
Front Axle Capacity: 3,600 lbs. each
Front Tire Capacity: 1,760 lbs. each
Front Stabilizer Bar Diameter: 1.25”
Front Shock Absorber Diameter: 1”
Front Brake Rotor Diameter: 11.86”
Front GAWR: 3,520 lbs.

Rear Spring Capacity: 2,000 lbs. each
Rear Axle Capacity: 3,750 lbs. each
Rear Tire Capacity: 2,800 lbs. each
Rear Shock Absorber Diameter: 1”
Rear Brake Drum Dimensions: 11.15” x 2.75”
Rear GAWR: 3,520 lbs.

GVWR: 6,200 lbs.
Curb Weight of vehicle: 4,564 lbs.
Difference = Payload: 1,636 lbs.

GCWR (w/3.73 axle ratio): 9,500 lbs.
GCWR (w/4.10 axle ratio): 10,500 lbs.
GCWR (w/4.56 axle ratio): 11,500 lbs.




Specifications for 1979 K20 @ 6,800 lb GVW w/350 4bbl V8/SM465 and Tubeless Tires --

Frame Section Modulus: 3.92

Front Spring Capacity: 1,850 lbs each
Front Axle Capacity: 3,800 lbs. each
Front Tire Capacity: 1,990 lbs. each
Front Stabilizer Bar Diameter: 1.25”
Front Shock Absorber Diameter: 25mm
Front Brake Rotor Diameter: 12.5”
Front GAWR: 3,700 lbs.

Rear Spring Capacity: 2,100 lbs. each
Rear Axle Capacity: 5,700 lbs. each
Rear Tire Capacity: 1,990 lbs. each
Rear Shock Absorber Diameter: 25mm
Rear Brake Drum Dimensions: 11.15” x 2.75”
Rear GAWR: 3,980 lbs.

GVWR: 6,800 lbs.
Curb Weight of vehicle: 4,738 lbs.
Difference = Payload: 2,062 lbs.




Specifications for 1979 K20 @ 7,500 lb GVW w/350 4bbl V8/SM465 and Tubeless Tires --

Same as those given for 6,800 lb GVW except for the following:

Rear Spring Capacity: 2,800 lbs. each
Rear Tire Capacity: 2,350 lbs. each
Rear Brake Drum Dimensions: 13.0” x 2.5”
Rear GAWR: 4,700 lbs.

GVWR: 7,500 lbs.
Curb Weight of vehicle: 4,816 lbs.
Difference = Payload: 2,684 lbs.




Specifications for 1979 K20 @ 8,400 lb GVW w/350 4bbl V8/SM465 and Tubeless Tires --

Same as those given for 7,500 lb GVW except for the following:

Front Tire Capacity: 2,780 lbs. each
Front GAWR: Remains at 3,700 lbs.

Rear Tire Capacity: 2,780 lbs. each
Rear GAWR: 5,560 lbs.

GVWR: 8,400 lbs.
Curb Weight of vehicle: 4,869 lbs.
Difference = Payload: 3,531 lbs.




There is some variability in terms of GAWR; individual pickups, as reflected by the decals affixed to the driver’s door pillar, might have different GAWR’s for a given GVWR than those shown above. This is because GM offered a number of different tire upgrades within each GVW package. For instance, your current K10 might indicate a front GAWR of 3,520 as shown above, or it might have been originally equipped with heavier duty tires (or the optional heavy duty front springs described below) that would warrant a higher rating. Regardless, your K10 will indicate a GVWR of 6,200 lbs.

It is important to understand that higher gross axle weight ratings allow a greater portion of the total load weight to be positioned over the front or back axle, as the case may be. However, the total weight of the load and vehicle should never exceed the gross vehicle weight rating of the vehicle, even though the sum of the stated front and rear GAWR's assigned to the vehicle may exceed the stated GVWR.

Not surprisingly, Chevrolet recommended the heaviest K20 model exclusively, with the 8,400 lb GVWR, for carrying large cab-over campers. Since you have only some parts left over from the original truck, you need to determine if your K20 had the heavier duty rear brakes and 2,800 lb rear springs that characterized this maximum GVWR. To do this, you will need to measure your brake drums and count the number of leaves in your rear spring packs. The 2,800 lb spring pack you need will have 7 leaves, while the lighter unit will only have 6 leaves. If you combine these components with the appropriate tire capacities (2,780 lbs +), theoretically you could achieve the 8,400 lb rating.

Chevrolet also advised prospective camper buyers to purchase the optional heavy duty front springs for K20’s expected to carry campers. These springs were rated at 2,250 lbs each and can be identified as they were comprised of 3 leaves vs. the standard 2 – leaf pack that was rated at 1,850 lbs. In an 8,400 lb GVWR K20, these optional springs would raise the front GAWR to 4,500 lbs. However, the total GVWR would remain at 8,400.

With respect to trailering capabilities, the GCWR’s shown within the 1976 K10 info presented above should be relevant. However, if you intend to tow a trailer or fifth wheel extensively there are some other issues to consider. But we will save that for later!

I hope some of this information is useful!

Ken Lewis