How to replace rusty rocker panels

Rust is the plague that infects everyone in the classic car hobby. We all talk about avoiding rusty cars, but let’s face reality: If no one was willing to fix any corrosion, there wouldn’t be many cars left to restore. 

And where does this metal cancer tend to strike? The rocker panels. Trapped moisture loves to breed in dark confines until it bursts free–and leaves a giant hole in its wake.

Just about all makes and models are affected, but fortunately the market has responded. Replacement outer rocker panels for our 1973 Triumph Spitfire, for example, cost just a hundred dollars per side from Victoria British. The labor to install them isn’t too specialized, and we had the entire job handled in a day.

1. This is what we’re trying to fix: common outer rocker panel rust. Fortunately, our inner rockers were in good shape.

2. The first step is to remove the seats, carpet and anything else that may be damaged by welding heat or spatter. The job is much easier if the doors are removed, too. 

3. To properly expose the spot welds that need to be drilled out, remove any paint and body filler in the area. Almost any sanding or grinding disc mounted to an air tool will do the job.

4. Next, drill out the spot welds. While a standard drill bit will work, a spot-weld cutter makes this task much easier. 

5. We have also busted spot welds with a homemade metal machete-type tool. All it takes is a solid whack with a hammer. 

6. The front of our Spitfire’s rocker panels were welded in place, so we cut them off. We then ground the old welds smooth.

7. The old, rotten rocker panel is now free. We’ve braced the door gap to keep the body straight and true while the rocker is away.

8. After removing the old rocker panel and grinding down the spot welds, the inner rocker should look something like this. Now it’s time to begin reassembly. 

9. All of that banging and drilling will bend the rocker panel tabs and edges. Use a dolly and hammer to smooth and straighten everything before test-fitting the new rocker panel.

10. To prevent future rust problems, coat the inner rocker with some type of rust inhibitor. We used 3M Mar-Hyde One-Step Rust Converter on this job. This stuff is nasty, so take appropriate measures to protect your skin, lungs and shop floor.

11. To protect the now-bare metal, we sprayed the entire repair area with Wurth Copper Weld Thru Primer. 

12. Time to prep the replacement rocker panel. First, we removed any paint to ensure a clean, strong weld.

13. We then test-fitted the new panel, using a hammer to make adjustments. When at this stage, make sure the door still opens and closes properly. 

14. Sometimes additional panels need to be removed to help adjust and fit the new rocker panel. Tom Prescott, owner of The Body Werks, recommended that we remove and then refit this small piece ahead of the rocker panel. Guess what? He was right. 

15. A commercial spot-welder is an amazing tool that will allow you to make a perfect repair. Assuming you don’t have this $10,000 piece of equipment in your shop, plug welds with a MIG or TIG welder will do an adequate job.

16. We used a MIG welder to spot-weld a patch panel on the rear quarter panel. This technique works on the rocker as well, where the spot welder won’t reach.

17. Now we’re in the home stretch. Once the rocker panel was welded in place, we went to work with a grinder to smooth out any welds that needed attention.

18. Voilà, our rocker panel repair is complete and ready for priming and painting. We completed both sides in less than a day.

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