Rocker panel rust is one of the most common body issues on 1988–1998 GMT400 trucks. Rockers take a constant beating from road debris, water, and salt. Here’s how to replace them.
What Is the Rocker Panel?
The rocker panel is the lower body panel that runs along the bottom of the cab, between the front and rear door openings. On the GMT400, rockers are exposed to constant moisture and road spray.
Signs You Need New Rockers:
- Surface bubbling along the lower edge
- Rust holes visible
- Rocker panels are soft to the touch
- Crusty, flaking metal at the lower seam
Rocker Replacement Options:
Option 1: Slip-On Rocker Covers (No Weld)
These are stamped metal pieces that slide over the existing rocker and are secured with screws or panel adhesive. They don’t remove the rust, they cover it. Not a permanent fix but a fast cosmetic repair.
Option 2: Weld-In Replacement Rockers
Full replacement rocker panels are available as reproduction parts. This is the correct long-term repair. Requires cutting out the old rocker and welding in the new one.
Step-by-Step for Weld-In:
- Remove all trim pieces (rocker moldings, step pads)
- Grind off spot welds at the top and bottom flanges
- Cut out the old rocker panel
- Clean up mating flanges – grind to bare metal
- Apply 3M Weld-Thru Coating to mating surfaces
- Clamp new rocker in position
- Tack weld and verify alignment with door gaps
- Complete welding – stitch weld to avoid warping
- Grind welds smooth, apply seam sealer
- Prime and paint
Cost:
- Reproduction rocker panels (per side): $80–$200
- Professional installation: $500–$1,200 per side
Prevention:
Apply rocker panel undercoating spray annually, especially before winter. Keep the drain channels clear so water doesn’t pool inside the rocker.
Have you done rocker panel work on your GMT400? Share your tips!