GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC Suburban - 4WD 🢒 Body and Accessories 🢒 Frame and Underbody 🢒 Frame Conditions
Table 1: Sag
Table 2: Buckle
Table 3: Sidesway
Table 4: Diamond
Table 5: Twist
Table 6: Improper Tracking
Table 7: Cracks in Web of Rails

Sag

Condition

Action

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

Straighten and reinforce the frame. Refer to Frame Straightening Description .

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

Buckle

Condition

Action

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

Straighten and reinforce the frame. Refer to Frame Straightening Description .

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.

Sidesway

Condition

Action

A collision involving the vehicle.

Straighten and reinforce the frame. Refer to Frame Straightening Description .

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.

Diamond

Conditions

Action

A collision involving the vehicle.

Straighten and reinforce the frame.

Refer to Frame Straightening Description .

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

Twist

Condition

Action

An accident or collision involving the vehicle.

Straighten and reinforce the frame.

Refer to Frame Straightening Description

Operating the vehicle on very rough terrain.

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 Wheel Alignment Measurement in Wheel Alignment.

The front or rear axle has shifted.

The wheel alignment is incorrect.

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. Re-tighten the bolts.

Concentration of stress that may result from many different factors.

Refer to Minimizing Frame Service Description .

Replace or weld and reinforce the rail.