134 How to Repair a 1968 Cadillac Pot Metal Bumper with Super Alloy 1
James C. From Maryland recently emailed this video of his 1968 Cadillac bumper repair using Super Alloy 1.
James is restoring a 1968 Cadillac convertible, and the front bumper wrap-around trim is busted in three sections. These vintage parts are constructed of pot metal and James had never repaired pot metal before, but decided to give it a go after watching Muggy Weld’s series of pot metal repair videos on YouTube.
As you can see, the Cadillac bumper still had the original chrome plating–which was not a deal-breaker when soldering adjacent to the chrome. Super Alloy 1 has a very low melting point of 350°F, which allows the product to flow out with damage to the chrome. If heat transfer is a concern, Super Alloy 1 pairs well with Heat Freeze Heat Paste.
Pot metal/zinc die cast is a soft alloy, so no special tools are required to prep the part prior to soldering. A dremel tool, file, or sanding disc, etc can be used to remove the oxidation and prep the work area. It is essential to clean the pot metal just before making your repair since pot metal oxidizes very quickly. It’s optimal to clean the parts the same day you plan to apply the solder.
After cleaning the part, be sure to create a bevel in the parent metal to allow the filler rod to adhere (top and bottom at the breakpoint).
A propane torch is sufficient heat for pot metal repair. If you’re using oxyacetylene, then use very little oxygen.
Use a brush to apply the flux or dip the rod into the flux and apply it to the work area. Keep the flux as close to the work area as possible for 2 reasons:
- you will drip less flux
- the part doesn’t have much time to cool between solder applications
Notice how James clamps the three broken pieces to a piece of steel. This technique helps align the parts while soldering the bumper.
One of the reasons Super Alloy 1 is a “must-have” product in the classic car restoration business is the unique liquid flux. Super Alloy 1’s rod works at half the melting point of pot metal/zinc diecast, and it’s flux transforms from honey colored to root beer brown when the parent metal reaches the proper working temperature. Essentially, it’s a visual temperature guide.
After making the repair and cooling the parent metal naturally, warm water and a wire brush can be used to remove the excess flux.
So how do you know if your part is pot metal or cast aluminum?
Pot metal is a zinc-based metal with almost a lead weight compared to aluminum, which is much lighter than zinc. You could also test the metal via TIG welding. The zinc will give off a purple hue when welded.
Thank you, James, for sharing your experience with Muggy Weld LLC products and giving Super Alloy 1 a shot at saving your vintage Cadillac bumper.