How to Install Flowmaster American Thunder Axle-Back Exhaust on your Mustang

1) Raise the vehicle and support securely with stands. To ease the removal of the stock system, spray a penetrating lubricant onto the rubber hangers just behind the rear differential and also at the rear of the vehicle. 

2) Begin by measuring back 2 ½” from the beginning of the straight area shown in the photo above and make a mark on both pipes. Support the exhaust system both in front and behind the area to be cut, then once you’ve double checked that the measurements are correct, cut both pipes at the marks. Note: Due to the closeness of the pipes to the gas tank, use caution when cutting! Using a 13mm wrench, unbolt the two hangers just behind the rear differential from the cross member. Carefully lower the stand under each muffler and slide the muffler assembly forward and out of the rear hanger mount. Lower the assemblies to the floor, leaving the front hangers attached. Carefully deburr the end of the pipes where cut with a file or die grinder. Finally, remove the two hanger mounts at the rear of the vehicle from the frame using a 13mm wrench, as you remove them place them with the factory muffler from the corresponding side. 

1) Place the new Flowmaster muffler units next to the factory units and swap the front and rear hanger mounts from the stock mufflers to the Flowmaster assemblies. Also, place a provided 2.50” clamp onto the inlet of each assembly. Tighten the clamp just enough to hold in place. 

2) Place the right muffler assembly #843048-363 up into position and slide the inlet completely onto the factory pipe. Support the assembly with a stand and remount the rear hanger mount to the frame and tighten securely. Remount the front hanger to the cross member and tighten securely. Leave the clamp on the inlet loose for now. Repeat this step with muffler assembly #843048-362 on the left side of the vehicle.

3) Adjust and level the two muffler assemblies to provide a satisfactory fit. A minimum of 1/2” clearance around all parts of the system must be maintained; while keeping suspension travel and vibration in mind. After adjustments have been made, you may now securely tighten the two muffler inlet clamps.

4) For a more secure installation, we highly recommend placing a minimum 1” weld on either side of the inlet slip-fit connections.