How to Retrofit Seatbelts

Written by shannon johnson
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Not all cars come equipped with seat belts. If you collect classic cars, remodel old versions, or build your own, you will need to know how to retrofit seat belts to make the car safe and legal to drive. Some cars have only lap belts, but these aren't the safest option, so you might consider changing the belts to shoulder belts. All of these processes involve retrofitting, which, simply put, means adding devices or equipment that were not previously there.

Skill level:

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Things you need

  • 3-point seat belt
  • Drill
  • Marker
  • Fine threaded shoulder anchor mounting plate
  • Center punch
  • 1/2 inch drill bit
  • 1/8 inch drill bit
  • 1-1/2 inch boring drill bit
  • Rivet Tool
  • 1/8 inch rivets with 3/8 inch reach
  • Anchor plug
  • Grade 5 hex bolts
  • Angle brackets
  • Wrench
  • Short bucket seat belt

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  1. 1

    Remove the panelling from the door where you will be installing the top of the three-point seat belt by following the instruction guide in your vehicle's owner manual. Every car will be different for removing the panelling, but once the frame is exposed, hold the mounting plate vertically in place between zero and 8 inches above and slightly behind the rear of the seat back.

  2. 2

    Hold the plate in place and mark the holes with a marker so that you have a drilling guide to mount your plate with. Make a mark along the bottom edge of the plate and then draw another mark one inch below that.

  3. 3

    Use a centre punch to make a dent at the centre of each of the markings, including the one an inch below the plate, to act as guides during drilling. Use a 1/2-inch drill bit to drill the centre hole and a 1/8-inch drill bit to drill the two holes above and below the centre. Starting at the centre of the lowest hole, use a 1 1/2-inch boring drill bit to cut a hole large enough for the mounting plate to pass through.

  4. 4

    Slide the mounting plate through the hole and up into the wall of the vehicle, making sure to line up the holes in the plate with the holes you have drilled in the metal. Use 1/8-inch rivets with a 3/8-inch reach to secure the plate to the frame.

  5. 5

    Replace the door panel, drilling the necessary holes so that there are openings in the panel that line up with the openings in the mounting plate. Plug the boring hole with a plastic or metal anchor plug, which can be found at most hardware stores.

  6. 6

    Install angle brackets at the floor points of the three-point seat belt. One should be mounted on the floor between the centre console and the seat of the car while the other should be mounted to the floor and outboard side directly underneath the mounted shoulder anchor. Use grade-five hex bolts to secure the angle brackets, making sure that the retractor box is bolted to the top side of the anchor underneath the shoulder point, while the bucket seat is bolted to the bracket between the chair and the console.

  7. 7

    Insert the shoulder bolt through the shoulder sash end and screw it to the mounting plate you installed earlier. Then thread a hex bolt through the end of the sash and through the retractor end and screw it into the outboard through the angle bracket. Make sure all bolts are tightened.

  8. 8

    Attach the bucket seat-belt end through the angle bracket to the manufacturer's mounting hole in the floor and tightly secure. Pop the cap cover over the top point of the shoulder mount, and you should be able to buckle yourself up from now on.

Tips and warnings

  • Cars vary as to what kind of retrofit they will need. This set-up is for the front seat of a car that has a door panel between the side window and the driver's window. The process is about the same, but where you will need to put your anchors can change by model.

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