Update 2020:
Check out our new video on how to install poly fenders using our poly fender kits.

We recently got an opportunity to mount a set of full tandem, 27″ drop fenders (FTF-27) for one of our favorite local trucking companies. After a week full of mild weather, the great state of Michigan gave us one of the first blizzards of the season to work on. It was snowing on and off for most of the install, but that didn’t stop us.

Mounting a pair or set of Robmar poly fenders is very straight forward. Some tools that you’re going to want to have on hand are; 2 clamps, handheld drill, ratchet(s) of appropriate size, and allen wrenches. Several 2×6 boards are very helpful when shimming the fenders up to the minimum required 1.5″ space when installing.

Like we stress in the instructions included with all mounting hardware kits, make sure that you dump your trucks air before installing. Also, you need to be aware of how much your truck is going to lower when loaded up. All of these factors can affect the operation of your fenders and might potentially cause damage if not taken into account.

Put your 2×6 spacers on each tire, then place your fenders on top of the spacers. You can use your clamps to connect the fenders, back to back, to make sure they’re not falling off the tires. Now, position the fenders until they are squared up with the truck and evenly aligned on top of the two axles. Use the position of the fenders to determine where you will mount the Center Bracket Assembly. It can go under either fender. It’s just a matter of preference and where you have mounting holes available.

Center Bracket Assembly

The first step in installing a half or full tandem setup is to begin with the Center Bracket Assembly. Remove the nuts and bolts from the top of the assembly and set them aside for now. Hold the assembly up to the truck to find a position that’s appropriate for mounting the Swing Arm. (The Swing Arm Assembly comes with HDPE spacers – use these as necessary when mounting, to avoid other bolts in the frame.) The Center Bracket holds up the flat sections of the fender(s) between your two axles. It’s adjustable up and down, as well as tilt-adjustable on the left and right sides. Make sure to not tighten any part of the assembly more then necessary until the installation is complete. Adjust the Center Bracket to the approximate final height.

Center Bracket Secured

You will need to drill 4 holes into the top, flat section of the fender to secure it to the Center Bracket. Use the existing holes in the top of the Center Bracket as a guide when drilling through the fender. After your holes are drilled, reinstall the nuts and bolts that you previously removed from the assembly. Once your have your fender mounted to the Center Bracket, you can begin installing the tube that will support the rounded side of the fender.

Offset Tube | MH-FT51

The offset tubes are a great choice and can save you from a lot of headache during the installation. The offset makes it easier to find a position that’s right for the fender, in a place where there might already be a hole available on the frame of the truck. Mount your tube, but don’t tighten it down all the way yet. You should still be able to swivel the tube to find your ideal position. Once you have a relative position that looks like it will work – slide 2 hangers onto the tube.
Hangers Pre-InstallPosition the hangers so that they are directly over the fender ribs. The hangers need to be installed onto the ribs because our custom washers, that will go on the underside of the fender, are designed to fit up into the rib (this is to provide extra space between the hardware and your tires.) Once you have located a good place for the hangers, make a mark in pencil to show where you need to drill. We drilled through the top of the fender, using the hanger as a guide. However, this isn’t the safest way and it could possibly damage your tire – so we don’t recommend doing it this way. It would probably be better to remove the fender before drilling.
Fender Hanger DrillingAfter drilling your holes, it’s time to secure the fender to the hangers. Push the elevator bolt through the elevator washer, then push it through the hole that you have drilled. Secure the exposed end of the elevator bolt with a washer and nylon nut.
Hanger TightenNow that you have your fender secured to the tube on the rounded side, and the flat side secured to the Center Bracket, you’re ready to add on the connecting fender. Put the connecting fender back onto the next tire, shimmed up with a 2×6 spacer. Clamp the fenders together back to back and get the Connector Plates ready.
Full Tandem Set Clamped TogetherNow, use the Connector Plate as a guide to drill 4 holes through the back of the fender. After you have your holes drilled, use the provided nuts and bolts to secure the fenders back to back – using the Connector Plates for added strength.

Repeat the above processes to mount the first fender on the opposite side of the truck. Then the final fender that connects to that. The final step in the process is to view your truck from as many angles as possible. Make sure that the fenders and brackets are all lined up properly with the truck and with the other fenders. Before moving the truck, check all of the connections to ensure everything is tightened up. Check the Center Bracket at its connection to the frame, the u-bolt connections, the mounting plate connections, and its connections to the fender. Check the tubes connections to the frame, and the hangers connection to the tube. (Make sure to only tighten the hanger 1/2 turn past the point of separation from the tube. (Any further tightening will damage the hanger.) Check that the hangers are properly tightened up to the fender. Finally, check that the fenders are properly secured together using the Connector Plates.

Full Tandem Installed