How to Repair Undercarriage Rust on a Truck

by Jenny Carver
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Rust eats away at metal until there are visible holes, or the structural integrity of the metal is no longer safe. Rust forms easiest where there is water, humidity, salt or mud against metal. The undercarriage of a truck is the most vulnerable place for rust to attack. Rust on the undercarriage should be repaired as soon as possible to prevent holes in the floor and other parts.

Step 1

Park the truck on a hard, flat surface, and engage the parking brake. Raise the truck, and place jack stands under the frame near each front tire. Lower the truck onto the jack stands.

Step 2

Crawl under the truck on your back, and use a wire brush to get rid of the loose rust. Reach in and around parts until you get most of the loose rust removed. You may also use a high-pressure hose, but you must wait until the undercarriage is completely dry before repairing it.

Step 3

Wipe wax and grease remover over every visible surface with a clean towel. This removes any last grease, wax or debris from the undercarriage.

Apply Rust Doctor (arguably the most user-friendly rust remover available) by brushing on a moderate coat. If any areas show through, apply another coat. Wait 24 hours for the Rust Doctor to dry if an additional coat is needed. The metal will begin to turn black, as it is converted into magnetite, which forms a protective barrier between the metal and moisture. It also prevents any further rust from forming.


  • When under a rusty undercarriage, always wear safety goggles to protect your eyes from rust and other debris.
  • The undercarriage can be painted after the project, but it is not necessary.


  • Don't use any type of acid spray or dip to remove rust. This can be used on small parts, if a neutralizing dip is also applied. Otherwise, the acid will hide in hard-to-reach places, eventually causing more rust.

Items you will need

  • Jack
  • Jack stands
  • Wire brush
  • Wax and grease remover
  • Towels
  • Rust Doctor
  • Paint brush

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