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Frame and Chassis

Frame Cutting – Be Careful!

Friday, November 18th, 2016

General Motors realized that after larger work trucks left the factory some owners would want to lengthen or shorten the side frame rails. Replacement beds would sometime require a different wheel base.

Therefore, as a warning GM painted or etched letters to tell owners the importance of a good, safe connection after the frame is cut. The attached photo shows a 1936 Chevrolet still showing this lettering on the inner frame rail. It is understood a similar warning is also on more modern trucks. Note: Even in the mid-1930’s the attorneys of General Motors were suggesting these warnings be visible to lessen laws suits!


1936 1 ½ ton from a farm in Western Kansas. Still displays the warning after 80 years! Seen just after the cut. Sorry photo does not help seeing the letters!

Before 1954

Wednesday, August 29th, 2012

Before 1954 on 1/2 tons, the frame rails were given a large arch as they passed over the rear axle housing. With a broken leaf spring or overloading the bed with too much weight, the frame rails will lower many inches before contacting an axle bumper. It was a system that worked for over 20 years on 1/2 tons when the frame rails were forced down toward the rear axle. A hard rubber axle bumper was placed under the hump in the frame to prevent metal to metal contact when this occurred.

For 1954 a totally redesigned pickup bed resulted in a three inch increased depth of the bed for more load volume. Some of this increase required a lower arch in the frame rail over the axle. There would be less space here so the rubber axle bumper was changed in length and was moved to the side of the frame. See photo!

Therefore, this prevents a correct interchange between the 1949-53 1/2 ton frame and the 1954 and newer frame. If this is done the beds will not have the correct relationship to the height of the cab.

1947 to 1953

1947 to 1953

1954 to 1955

1954 to 1955

Overload Rear Bumpers

Thursday, February 11th, 2010

To help prevent metal to metal contact when 1/2 and 3/4 tons are overloaded or have weak shock absorbers, truck manufacturers used a rubber devise. This cushion prevents the axle from making direct contact with the frame rails.

On the rear of the 1947-1953 GM pickups, it attaches directly to the underside of the hump in the frame. It is not meant to be removed during the life of the truck.

In 1954 a change in the overload bumper location was necessary. This was the first year for a redesigned step bed which was three inches deeper. To keep the top edge of this new bed the same as earlier years, the hump in the frame was lowered. It was necessary to place a bracket on the side of the frame rail and add this bumper. The attached photo shows this repositioning of the overload bumper.

overload rear bumpers 1

1947-1953 (above)

overload rear bumpers 2

1954-1955 (above)

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Chevy and GMC Frames

Thursday, February 11th, 2010

These are some very rare photos. It is quite unusual to find 1947-1953 Chevrolet and GMC 1/2 ton bare frames together. Here, you can cmpare the differences in the front cross members.

As the GMC six cylinder is a few inches longer than the Chevrolet, engineers designed two different front engine cross members. In building the truck frame for the assembly line a different cross member was added depending if it was to be in a Chevrolet or GMC factory.

This is why re-builders of GM trucks today develop immediate problems when they exchange 6 cylinder engines between the Chevrolet and GMC. The two makes may look about the same in any year, however the power plant causes changes not only in the frame’s front cross members as well as sheet metal in this immediate area.

chevy gmc frame 1

chevy gmc frame 2

chevy gmc frame 3

Photos courtesy of Rob English

Email: rob@oldgmctrucks.com

Website: Oldgmctrucks.com

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