Talk to an Americanmuscle Rep
Mon - Sun, 8:30 AM EST - 11:00 PM EST

Free Shipping On Orders Over $49. Details

How to install a Flowmaster Force II Dual Catback Exhaust for your 1999-2004 Mustang

Installation Time

2 hours

American Muscle
Shop Parts in this Guide



1. Disconnect the negative side of the battery cable. 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. Using a hacksaw or sawsall, cut the stock tailpipe off approximately 2” behind the muffler case.

3. Separate the tailpipe hangers from the rubber mounts at the rear of each tailpipe. A lubricant may ease removal. Remove tailpipe.

4. Support the stock muffler with a stand. Remove the two nuts at muffler to catalytic converter connections.

5. Separate steel muffler hanger on the rear of the muffler from the rubber mount on the vehicle and remove the stock muffler from the vehicle.


1. Before installing anything, prep the clamps supplied in the hardware kit by removing the nuts, and applying a thick lubricant such as white grease or anti-seize to the threads.

2. Bolt up hanger #363HA on right side of vehicle body underneath back seat, just like the left side factory hanger. Use the supplied 5/16” x 3/4" bolts, lock washers and nuts and tighten firmly.

Then place the two supplied rubber hangers #HA168 onto the hanger rods you just bolted to the body.

3. At the rear of the vehicle behind the bumper in each corner on both sides place a supplied 5/16” x 3/4" bolt with flat washer up and down into the factory inner holes. Place hanger #HA602 up onto the bolts along with the 5/16” flat washers, lock washers and nuts supplied in the parts kit. The rubber hangers should face the outside of the vehicle. Tighten both hangers securely into place.

4. Take the Y-pipe/muffler assembly #16326 and place it up in muffler location under car seats and slide hangers welded to muffler into the rubber mounts under the back seats (the one you bolted on and stock hanger.) Bolt the front end with flange to the stock flange behind the catalytic converter. Tighten enough to hold, but still allow for adjustment.

5. Take the left side tailpipe #16328 and maneuver it over the rear axle (from rear to front). Slide hanger welded to tailpipe stainless into rubber mount at rear of vehicle. Slide front end of tailpipe into outlet of muffler and slide hanger into rubber hanger by muffler. Repeat this step for right side tailpipe #16327 (jacking the body up may make it easier to install tailpipe over the axle). Place a 2 1/2" clamp on outlet of muffler and tighten enough to hold, but still allow for adjustment.

6. Adjust the position of the muffler and tailpipe to provide adequate clearance for suspension travel. Maintain a minimum of 3/4” clearance between the Flowmaster system and the drivetrain and chassis components.

7. Tighten down all clamped connections securely. After the system is secure, slide the hanger keepers onto both the hanger rods above the muffler outlet. This will prevent the hangers from slipping out of the rubber mounts.

8. For a cleaner appearance and more secure installation, we highly recommend welding all slipfit connections. If you live in a geographical area that has harsh winters or sees a great deal of precipitation, the use of high temperature paint over the welded areas can help to prevent surface rust and premature corrosion.


QtyDescriptionPart #
Box 1 of 2 (5019)
1Y-Pipe/Muffler Assembly16326
Box 2 of 2 (1027)
1Tailpipe, Left16328
1Tailpipe, Right16327
1Parts KitPK368
1Muffler Hanger, Right363HA
2Tailpipe Hanger, Left & RightHA602
22 1/2" ClampsMC250S
2Rubber HangerHA168
45/16” x 3/4” Bolt
45/16” Lock Washer
45/16” Nuts
67/16” Hanger Keepers