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How To Install Fenders On A Semi-Truck? (Ultimate Guide)

Driving a semi-truck requires you to familiarize yourself with its parts and hardware to ensure safety. And one of the parts that you should take the importance of is the fenders.

Fenders protect the semi-truck from debris such as dirt and rocks kicked up by its tires. Aside from that, they also make the semi-truck look more relaxed and pleasing.

Knowing how to install fenders on your semi-truck will provide you, your semi-truck, and other drivers on the road with a safer driving experience.

Here’s a Short Summary of How to Install Semi Truck Fenders:

Fenders on a semi-truck can be installed by first letting the air out of the suspension. Ensure the new fenders are well sized for the truck. Align the fender and install brackets into position, while maintaining a space between the tires. Tighten the screws and check to ensure the fender is secure.

How are Semi-Truck Fenders Measured?

Size matters when installing fenders to prevent them from hitting the tires and will look good once installed on your semi-truck.

To ensure you get the right size, measure the fenders’ length, height, and width.

To get the length, measure the fender across from lip to lip. For the height, you can do it by measuring the lower lip of the fender to its top.

While for the width, you can get it by measuring the outside lip of the fender to its trailer wall.

How to Join Fenders for a Full Fender?

If you already have a half tandem axle fender, you can join or pair it to become a full tandem axle fender.

With the use of a clamp, align both the two similar fenders. Then, drill mounting holes through both of them. Insert connector bolts and fender washers. 

Do not forget to tighten the connectors using bolt nuts.

How to Measure Fender Clearance from the Tire and Fifth Wheel?

There should be enough space between the tires and the fifth wheel to avoid encountering problems when driving your semi-truck.

Using spacer blocks, ensure a minimum of three inches of fender clearance from the tire and the fifth wheel to have adequate space for bumps and potholes you may encounter on the road.

If the space is less than the recommended measurement, the wheel will surely keep hitting the fenders and may cause an accident when driving.

Where to Install the Brackets on the Frame?

To know where to install the fender brackets, you can do it by having the fenders in position.

Mark and test-fit the fender brackets to the desired position on the frame. You should also ensure that you align the bracket with the existing bolt holes in the frame.

How to Line up the Bracket with the Fender?

You can place the fenders on spacer blocks above the tires to provide a one, and a half inches recommended clearance. Once set, you can test the position or line up the brackets.

After setting the brackets in the proper position, you can tighten them up using a 5/8 inches by four and a half-inch bolt that goes through the swivel bracket.

You can use a 160 to 170 foot-pounds torque since it is more recommended.

Here’s a cool video on how to install a semi-truck fender:

How to Install Lights on the Fender?

Another feature that makes the fender look more extraordinary and functional is that you can attach a light to it to add illumination or a signal while driving, especially at night.

To install a light on the fender, mark where you will place it. The most recommended should be near the wheelbase.

Next, open the wheelbase trunk liner. It will give you more space to install the lights since there should be no obstruction, especially in the back.

You can use a colored painter’s tape to protect nearby parts from scratches before you start drilling.

Once you are ready, drill the hole. Ensure the holes are big enough to accommodate the stem of the light or the wires. Also, you must be sure that you are drilling the hole in a flat area.

After drilling, insert the adapter. For each side of the fenders, separate the positive from the negative wires. Then, wire all the positive wires together. Do the same for the negative wires.

Ensure you wire them up parallel and tap them to the tail light wires. Once you turn on the headlights, the light you just installed on the fender will also turn on.

Conduct several tests and adjustments if it did not work on your first attempt until you ensure everything works well.

How to Install Mud Flaps on the Fender?

The fenders will work best if it has mud flaps attached to them. As its name suggests, it reduces the amount of mud splashing all over the place while driving. It is essential when driving in rainy conditions or on a muddy surface.

To install mud flaps on your semi-truck fender, you can choose between non-drilling and mud flaps that need drilling.

Installing non-drilling mud flaps can be the easiest. All you need to do is to clean the surface where you will attach the mud slaps. Then, create a clearance between the tire and the wheel.

Test the mud flaps by holding them up and comparing their shape to fit your allotted space. You can also check for markings like “LH” and “RH” for appropriate placement.

Since it is a non-drilling mud flap, there is already a factory-drilled hole in the wheel well of your semi-truck. Look for these holes and place the flaps into place.

Ensure you tighten the screws, and you finally have mud flaps installed on the fenders.

For mud flaps that need drilling, follow the steps mentioned, except if your semi-truck does not have the drilled holes, you can put the flaps in place.

Thus, it would help if you drilled the holes yourself before installing the mud flaps.

How Long should Mud Flaps be?

When choosing a mud flap to attach to your semi-truck fender, you need to ensure it has the appropriate size so it will not be blocking the wheels when driving.

The ideal size of the mud flaps should not be more than eight inches above the road surface and will not exceed 15 inches when the semi-truck is in unloaded condition.

How to Check if the Fender Needs Reinforcing?

Like parts and hardware in a semi-truck, the fenders also require regular inspection.

Your semi-truck fenders may need reinforcing if you see the bolts loosen or if some dents or scratches are on their surface.

You need to tighten the screws immediately if you see them loosening or replace a new fender if there are already a lot of dents and scratches.

How to Reinforce the Fender?

Reinforcing the fender as soon as you see splits, dents, scratches, and some other issues will prevent it from further damage.

First off, wash the fender so you can see the damage. If you see splits and dents, you can pull them together using a high adhesive masking tape.

Get a plastic weld solution and spread it on the split area to seal it. You can also use an aerosol hardener to apply directly to the plastic weld solution.

Fill the remaining creases and dents with the polyester-based plastic body filler.

Once done with the fillers, rub them down with a grit paper to flatten out the surface. Clean the fender again to get rid of dust and start priming or painting the fenders for a newer look and smooth finish.

What are Full Fenders?

Full fenders have pleasing designs to protect semi-trucks from common debris such as rocks, mud, sand, and liquids.

The primary function of full fenders is for dual-wheel axle coverage of both wheels.

What are Half Fenders?

Installing half fenders is a good option if you want an alternative to full fenders.

Half fenders do not cover both wheels of a dual-wheel axle semi-truck but can still offer a fair amount of protection and coverage from debris.

They are also less expensive and less obstructive compared to full fenders.

What are Quarter Fenders?

A quarter fender is suitable if you prefer a smaller fender or if your semi-truck only has one wheel axle setup.

Quarter fenders are useful for semi-trucks with only a single axle setup.

They may only offer minimal protection from spray and debris, but they are the least expensive and obstructive among the three.

What are the Best Semi-truck Fender Kits?

It is hard to label which of the available semi-truck fender kits is best for your rig.

You can rely on popular manufacturers like Minimizer and Hogebuilt for high-quality semi-truck fenders.

But if you can look for other options which you think are more affordable but has similar qualities to the known brands, then you may do so to protect your semi-truck.