WRX/STI VA 3.5" Double Wall Axleback: Bolt-On Fit Check

By REMARK Exhaust | Published: 2026-11-02

Category: How-to Guides

A step-by-step fit check for installing a 3.5" double wall axleback on a 2015-2021 Subaru WRX/STI VA, covering flange, hanger, and tip clearance.

Quick answer

Test-fit the axleback before tightening anything: slide the flange over the stock mid-pipe studs, hang the muffler can from the factory rubber isolators, then check tip clearance to the bumper. Tighten only after all three points line up.

Why the VA chassis needs a dry fit first

The 2015-2021 WRX/STI VA has a short rear section, so a 3.5" tip leaves little room for error at the bumper cutout. If you tighten the flange before the hangers are seated, the muffler can pull to one side and the tip will sit crooked or rub. A dry fit lets you see the final position with the hardware loose, then adjust before torque.

This guide assumes you are reusing the factory mid-pipe and installing an axleback that includes gaskets and hardware, as the REMARK VA axleback does. If your car has an aftermarket mid-pipe or a different rear bumper, check those interfaces first.

Tools and parts to have on the ramp

You need a 14mm socket and wrench for the factory flange nuts, a 12mm or 14mm for the hanger bolts if your axleback uses them, penetrating oil, a wire brush, and a torque wrench. A second pair of hands helps hold the muffler while you start the flange nuts. Have the new gasket and hardware within reach; missing hardware is the most common reason a fit check turns into a second trip to the parts store.

When the stock flange or hanger is the real problem

If the flange studs are heavily rusted or the rubber isolators are stretched, no axleback will sit right. Inspect the mid-pipe flange surface for pitting and replace cracked isolators before judging tip clearance. On a used axleback, minor scratches and blemishes are normal and do not affect fit, but a bent hanger rod or a warped flange does.

Bolt-on fit check steps

Lift and support the rear: Raise the rear of the car on ramps or jack stands so you can reach the flange and hangers. Spray penetrating oil on the factory flange nuts and let it sit while you gather tools. Never work under a car held only by a jack.
Remove the stock axleback: Unbolt the flange from the mid-pipe, then pry the hanger rods out of the rubber isolators. Keep the factory nuts and note which isolator each hanger came from. If a hanger rod is bent, replace it before installing the new axleback.
Clean the mating surfaces: Wire-brush the mid-pipe flange face and the new axleback flange. A clean, flat surface is what lets the gasket seal without over-tightening. Do not reuse a crushed or delaminated gasket.
Dry-fit the flange and hangers: Slide the new gasket on, push the axleback flange over the studs, and start the nuts by hand. Then seat each hanger rod into its rubber isolator. Leave everything loose. If the flange will not sit flush, stop and check for a misaligned stud or debris.
Check 3.5" tip clearance: Look at the gap between the double wall tip and the bumper cutout on all sides. Shift the muffler can on the hangers until the tip is centered and has even clearance. A tip that touches the bumper will melt or crack the plastic once hot.
Torque the flange: With the tip centered, tighten the flange nuts evenly in a cross pattern to the factory spec for your model year. Do not guess the torque if you do not have the spec; snug and check for leaks. Recheck tip centering after final torque; tightening can pull the muffler sideways.
Start up and listen: Start the engine and listen for a tick or hiss at the flange. A leak means the gasket is not seated; loosen, reseat, and retighten. Recheck flange nut torque after the first few heat cycles.

Product facts

Axleback (3.5") Double Wall - Subaru WRX/STI VA [2015-2021]: Fits 2015-2021 Subaru WRX/STI (VA) and includes gaskets and hardware. You can complete the fit check without sourcing a separate gasket or nut kit.
Axleback (3.5") Double Wall - Subaru WRX/STI VA [2015-2021]