The Bilstein B6 (HD) 36mm monotube rear shock, part 24-215220, is a single-tube replacement damper listed for the 2004–2009 Mazda 3 and the 2007–2009 Mazdaspeed 3. Monotube construction keeps the working fluid and gas in one cylinder, which helps the damper hold its feel through repeated compressions on back roads or autocross laps better than a basic twin-tube unit. Listings describe this as a front-wheel-drive application, so all-wheel-drive owners should verify fitment before ordering. A Bilstein name-brand build is the main reason to pay more than generic rear shocks, since a worn stock damper can let the rear end wallow during quick transitions. Searching for a Mazda 3 rear monotube shock, Mazdaspeed 3 rear damper upgrade, or Bilstein B6 rear shock for track days will bring up this exact part number.
Installation is a bolt-on job with the rear wheel off and the car safely supported on jack stands. Owners on user forums describe removing the lower bolt first, then the two nuts inside the wheel well at the top of the shock, and reusing the original bump stop and dust cover on the new unit. Expect the lower stud to resist removal on older cars, so penetrating oil and patience help. Those who have stripped or broken a top mount recommend ordering a replacement mount before starting, because repairing a damaged mount is far more time-consuming than the shock swap itself.
The product name lists both, but listing details for the Mazdaspeed 3 years vary across sellers. Confirm the application with the manufacturer against your VIN before ordering.
Owners on user forums commonly move the original bump stop and dust cover onto the new shock during installation.
Owners on user forums note the two top nuts need only modest torque, and that a snapped stud can be difficult to remove because it is welded from the inside.
This is a moderate DIY job for someone comfortable with a floor jack, jack stands, and a socket set. Plan on soaking the lower bolt in penetrating oil before you start, since owners on user forums report it can be seized and need a breaker bar or impact tool. Reach the upper nuts from inside the wheel well, avoid overtightening them, and consider anti-seize on the lower stud when reassembling. If the factory upper mount is cracked or its stud is broken, replace the mount before installing the new shock.
