GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C Pickup - 2WD 🢒 Body and Accessories 🢒 Frame and Underbody 🢒 Frame Conditions

Frame Conditions Sag

Sag

Condition

Action

Loads greater than the frame is designed to carry causes sag.

Straighten and reinforce the frame. Refer to Straightening Frames.

Uneven load distribution causes sag.

Abrupt changes in the section modulus.

Improper body, or accessory mounting, which may include the following:

    • Holes drilled in the flange of the frame rail.
    • Too many holes in the web section of the rail.
    • Holes in the web section which are too close to each other.
    • Four or more holes in the same vertical line of the rail web.
    • Welds on the flange, particularly across the flange or along its edge.
    • Cutting holes in the rail with a torch.
    • Cutting notches anywhere on the rails.

A collision involving the vehicle causes the following conditions:

    • Sag
    • Buckle
    • Sidesway
    • Diamond

The use of equipment for which the frame has not been designed or reinforced causes the following conditions:

    • Sag
    • Buckle
    • Sidesway

Frame Conditions Buckle

Buckle

Condition

Action

Using equipment like snow plows for which the frame was not designed.

Straighten and reinforce the frame. Refer to Straightening Frames.

A collision involving the vehicle.

A fire involving the vehicle.

Abrupt changes in section modulus.

Improper body, or accessory mounting, which may include the following:

    • Holes drilled in the flange of the frame rail.
    • Too many holes in the web section of the rail.
    • Holes in the web section which are too close to each other.
    • Four or more holes in the same vertical line of the rail web.
    • Welds on the flange, particularly across the flange or along its edge.
    • Cutting holes in the rail with a torch.
    • Cutting notches anywhere on the rails.

Frame Conditions Sidesway

Sidesway

Condition

Action

A collision involving the vehicle.

Straighten and reinforce the frame. Refer to Straightening Frames.

A fire involving the vehicle.

The use of equipment such as snow plows for which the frame was neither designed nor properly reinforced.

Abrupt changes in section modulus.

Improper body, or accessory mounting, which may include the following:

    • Holes drilled in the flange of the frame rail.
    • Too many holes in the web section of the rail.
    • Holes in the web section which are too close to each other.
    • Four or more holes in the same vertical line of the rail web.
    • Welds on the flange, particularly across the flange or along its edge.
    • Cutting holes in the rail with a torch.
    • Cutting notches anywhere on the rails.

Frame Conditions Diamond

Diamond

Conditions

Action

A collision involving the vehicle.

Straighten and reinforce the frame. Refer to Straightening Frames.

Towing another vehicle with a chain attached to one corner of the frame.

Frame Conditions Twist

Twist

Condition

Action

An accident or collision involving the vehicle.

Straighten and reinforce the frame. Refer to Straightening Frames.

Operating the vehicle on very rough terrain.

Frame Conditions Improper Tracking

Improper Tracking

Conditions

Action

The frame is out of alignment.

Replace or weld and reinforce the rail. Ream the bolt holes. Replace with larger bolts if necessary. Retighten the bolts.

Replace or weld and reinforce the rail.

Refer to Front Wheel Alignment in Steering.

The front or rear axle has shifted.

The wheel alignment is incorrect.

Frame Conditions Cracks in Web of Rails

Cracks in Web of Rails

Conditions

Action

Loose crossmember attaching bolts.

Replace or weld and reinforce the rail. Ream the bolt holes. Replace with larger bolts if necessary. Retighten the bolts.

Concentration of stress that may result from many different factors.

Refer to Minimizing Frame Damage and Reinforcements.

Replace or weld and reinforce the rail.