The Wilwood AERO4 rear big brake kit bolts to the OEM rear axle and reuses the factory parking brake assembly, pairing forged four-piston W4AR calipers in black powder coat with 14.00-inch GT slotted rotors to add stopping capacity behind 18-inch and larger wheels on the BMW E90 325i and 328i. The Spec-37 iron rotors run a 72-curved-vane internal design with a black electro-coat finish, and the kit ships with BP-20 compound pads, parking-brake mounting hats, and a rear stainless flexline kit. Caliper output is matched to the OE master cylinder, ABS function, and factory brake bias.
| Type | AERO4 four-piston rear big brake kit for OE parking brake |
| Position | Rear axle |
| Caliper | W4AR forged AERO4 4-piston, black powder coat |
| Rotor | 14.00 in (355mm) GT slotted, Spec-37 iron, 72 curved vane, black electro coat, 1.10 in thick |
| Pads | BP-20 compound |
| Contents | Calipers, rotors, parking-brake mounting hats, BP-20 pads, mounting hardware, rear stainless flexline kit |
| Min. Wheel Diameter | 18 in |
| Quantity | Complete rear axle kit (pair) |
Documents: Installation Instructions (PDF)
This part fits:
| Year | Make | Model | Submodel |
|---|---|---|---|
| 2006 | BMW | 325i | Base |
| 2007-2013 | BMW | 328i | Base |
