How to Install Flowmaster Force II Cat-Back Exhaust - Single Side Exit (14-17 4.3L Sierra 1500) on your GMC Sierra

1) Raise the vehicle up on a hoist or rack to working height. If you do not have access to a hoist or rack raise the vehicle and support securely with jack stands. 

2) Support the muffler with a stand. Using a hacksaw or sawsall, cut the stock tailpipe off just behind the muffler. Separate the wire hangers on the tailpipe from the rubber mounts on the vehicle and remove the tailpipe from the vehicle. This step is not mandatory but makes removal easier. 

3) Using a 15mm wrench, loosen the bolt on the clamped ball connection behind the catalytic converter. Separate the wire hangers from the rubber mounts on the vehicle and lower the inlet pipe and muffler from the vehicle. A lubricant will make removal much easier. You will need to remove the ball clamp from the stock system; it will be reused with the Flowmaster system.

1) Place inlet pipe assembly #26401S into position onto the ball connection behind the catalytic converter. Reinstall the clamp onto the ball connection and tighten enough to hold, but still allow for a small amount of adjustment. Connect the hanger on the pipe to the rubber mount on the vehicle. 

2) If installing the system on a Crew Cab truck with a 6.5’ bed, place extension pipe #TB700S onto the back of the #26401S inlet pipe, place a provided clamp onto the slip-fit and tighten enough to hold in position. The extension pipe will not be used on Double Cab-6.5’ bed or Crew Cab-5.5’ bed models.

3) Place a supplied 3” clamp over the inlet of the muffler, then slide the inlet of muffler onto the back of the inlet pipe. Use a stand to support the muffler. Tighten the clamp just enough to hold in position. 

4) Slide a 3” clamp onto the muffler outlet neck. Place tailpipe #26410S into position over the axle and insert the hangers at the front and rear of the pipe into the rubber mounts on the vehicle and slide into the muffler outlet. Tighten the clamp just enough to hold, while still allowing for adjustment. 

5) Place the stainless tip #ST462 onto the end of the exit pipe and adjust to the desired location. Then tighten the tip enough to hold, but still allow for adjustment. 

6) Adjust the position of all the pipes and muffler to provide a satisfactory fit. A minimum of 3/4” clearance around all parts of the system must be maintained; while keeping suspension travel and vibration in mind. After adjustments have been made, securely tighten all clamps and install the 4 1/2” hanger keepers onto the hanger rods. 

7) For a more secure installation, we highly recommend welding all slip-fit connections.