How Suspension Bolts Work

Attaching wheels to a car body is easy when you're playing with those building blocks for kids. Connecting a real suspension system to a vehicle or trailer, however, isn't as simple. Different connections involve the use of different bolts. Below, we'll examine the main types of suspension bolts you'll find in a suspension system.

Shackle bolts: Shackle links are one way automakers connect the vehicle body to the wheels. As you can see in the adjacent image, one side of each shackle link hinges to the vehicle and the other to the suspension. Nuts screw down over the ends to prevent the bolts from sliding off, and grease keeps these parts moving freely.

U-bolts: These horseshoe-shaped bolts loop over or under a vehicle's axle, while the ends screw firmly into nuts on the other side of a metal plate. Carmakers use this arrangement to fix bow-shaped leaf springs snugly against the axle. To learn more, read How Leaf Springs Work.

Spring eyebolts: While U-bolts attach the center of a leaf spring to the axle, eyebolts attach the ends of the spring to the vehicle or trailer body. These simple bolts slip through round eyes at either end of the bow-shaped leaf spring, as well as through round hanger holes on the frame.

Spline bolts: When you want a bolt to fasten something without rotating, then this is the hardware for you. Spline teeth extend from the sides of the bolt, securing it. Frequently, they're used to lock shock absorbers in place.

Equalizer bolts: Equalizer hitches apply leverage across the trailer tongue and towing vehicle, distributing heavier loads more evenly. Equalizer bolts simply secure these hitches. Some models feature a cotter pin, which slides through the end of the bolt and the castle screw to keep the nut from sliding off the end.

On the next page, we'll explore how to use suspension bolts.

If you're installing suspension bolts to hold your suspension system together and connect it to the vehicle or trailer, then congratulations. You are using suspension bolts for their intended purpose. Just remember that certain bolts are designed for very specific parts of the suspension. If you need to replace a bolt, you'll want to make sure you have the right size and variety of bolt required.

If you decide to replace suspension bolts on your own instead of taking your vehicle or trailer to a professional garage, make sure to take precautions. Before you disassemble even part of your suspension system, be certain to support the vehicle or trailer body off the ground in the same way you would if you were changing a flat tire. Never place jacks or supports on the suspension system itself. You want to elevate the heaviest part of the trailer or vehicle (the body), so you can work on the much lighter suspension.

Bolts designed to rotate, such as shackle bolts, require greasing so they can move. As with any lubricated mechanical part, occasionally you may need to reapply the grease. On many modern vehicles, these parts are sealed effectively for life, but older vehicles and trailers sometimes require greasing through vehicle or grease zerks (also known as grease nipples or grease fittings). These tiny holes can accommodate the tip of a grease gun. If your vehicle or trailer features these fittings, you'll want to apply more of the manufacturer-recommended lubricant regularly.

Explore the links on the next page to learn even more about towing.

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