AP Racing by Essex 2001-2006 BMW E46 M3 Competition Brake Kit (Rear CP8350/325mm)
or as low as $270.75/mo with Affirm
AP Racing by Essex
Competition Brake Kit Rear CP8350/325mm — BMW E46 M3
Purpose-built rear competition brake kit for the 2001–2006 BMW E46 M3. Four-piston fixed calipers replace the OE single-piston sliding caliper, delivering dramatically improved thermal capacity, modulation, and fade resistance for dedicated track use.
Track-Focused Rear Upgrade
Serious Rear Braking for the BMW E46 M3
The E46 M3's OE rear brake is a single-piston sliding caliper with a 328x20mm disc. It works fine on the street, but sustained track use exposes its limits quickly: inconsistent clamping force, thin disc thermal capacity, and rapid fade under repeated heavy braking. This kit replaces it entirely with a proper fixed-caliper competition system.
The CP8350 four-piston fixed caliper delivers uniform pad pressure across the entire friction surface, saving nearly 3 lbs per caliper versus the OE unit. The 325x32mm two-piece floating disc is 12mm thicker than stock with more than double the internal vanes (70 vs 30), providing vastly superior heat absorption and dissipation despite a slightly smaller diameter.
Important: This kit removes the OE parking brake mechanism. It is designed for track-focused vehicles where a hydraulic handbrake or dedicated parking solution is used. Not recommended for daily drivers that rely on the cable-actuated parking brake.
Key Advantages
Engineered for Track Duty
Eight reasons this kit transforms E46 M3 rear braking
4-Piston Fixed Caliper
Replaces the OE single-piston sliding caliper with a proper four-piston fixed design. Equal 28.575mm pistons deliver uniform clamping force across the entire pad surface for consistent braking.
Hard Anodized Finish
Hard anodizing grows an extremely hard aluminum oxide layer directly from the base metal via electrical current through an acid bath. Far more durable than paint or powder coat at sustained track temperatures. Will not chip, flake, or degrade under heat.
60% Thicker Disc
The 325x32mm disc is 12mm thicker than the OE 328x20mm unit. That 60% increase in thickness translates directly to greater thermal mass, higher heat absorption capacity, and dramatically improved fade resistance on track.
~5 lbs Lighter
Despite the thicker disc, the total rear axle assembly saves approximately 5 lbs versus stock. The CP8350 caliper alone saves nearly 3 lbs per side (4.8 vs 7.65 lbs OE), and the aluminum hats offset the heavier iron rings.
70-Vane J Hook Discs
More than double the OE 30-vane count. 70 directional vanes dramatically improve internal airflow and heat evacuation. The J Hook slot pattern provides uniform heat distribution with more leading edges for consistent bite.
Stainless Steel Pistons
Stainless steel pistons (not aluminum) create a superior thermal barrier that keeps heat out of the brake fluid. Maintains firm, consistent pedal feel through extended track sessions without the fluid boil risk of aluminum pistons.
2-Piece Floating Discs
6061 hard-anodized aluminum hats with 10-bolt floating attachment and anti-knockback spring clips (5 per disc). Allows radial thermal expansion without coning or warping that plagues one-piece discs under track heat.
Spiegler Brake Lines
DOT-compliant stainless steel brake lines included in every kit. Improved pedal feel with abrasion-resistant coating for long-term durability and a lifetime warranty from Spiegler.
Complete Kit
What's In The Box
- AP Racing CP8350 Calipers (Pair)4-piston fixed, 4.8 lbs each (no pads) — hard anodized finish with stainless steel pistons, AKB springs, and high-temp seals
- AP Racing 325x32mm J Hook Discs (Pair)70 directional vanes — 2-piece floating with 6061 hard-anodized aluminum hats, 10-bolt attachment, and anti-knockback spring clips (5 per disc)
- Caliper Mounting Brackets & HardwarePrecision-machined brackets with aircraft-quality mounting hardware for the E46 M3 rear
- Spiegler Stainless Steel Brake LinesDOT-approved with abrasion-resistant coating and lifetime warranty
- Installation InstructionsStep-by-step guide for proper fitment and torque specifications
- Not Included: Brake PadsFerodo Racing D50 pads sold separately — DS2500, DS1.11, DS3000, DSUNO, or DS3.12 (+$125 each)
- Not Included: Pad Tension ClipsOptional add-on for additional pad retention (+$39.90 for pair)
Technical Data
Specifications
Caliper (CP8350)
4-Piston Fixed CompetitionDisc (325x32mm)
70-Vane J Hook Racing DiscEngineering
Technology Deep-Dive
Fixed vs. Sliding Caliper
The OE E46 M3 rear uses a single-piston sliding caliper that relies on bracket pins to pull the outboard pad into the disc. This design produces uneven pad wear and inconsistent clamping force. Under track heat, the pins can bind and further degrade performance.
The CP8350 four-piston fixed caliper applies force directly and equally to both pads simultaneously. No sliding mechanism, no pin binding, no uneven wear — just consistent, predictable braking force every lap.
Hard Anodized Finish
Paint and powder coat degrade under sustained track heat. Hard anodizing passes electrical current through the aluminum caliper body in an acid bath, growing an extremely hard aluminum oxide layer directly from the base material. The result is an integral protective surface that cannot chip, flake, or separate.
Hard anodized surfaces are significantly harder than the base aluminum and provide excellent corrosion resistance, thermal stability, and abrasion protection through thousands of track miles.
32mm vs. 20mm Disc Thickness
The OE E46 M3 rear disc is 20mm thick. The AP Racing disc is 32mm — a 60% increase. While the AP disc weighs slightly more than the OE disc ring (15.93 vs 14.94 lbs), that extra mass is iron thermal capacity where it matters most: absorbing and dissipating heat.
Combined with 70 directional vanes (vs 30 OE), the result is a disc that can absorb dramatically more heat before reaching critical temperatures, giving you more laps before fade becomes an issue.
Stainless Steel Pistons
Stainless steel construction (not aluminum) provides a superior thermal barrier that keeps heat out of the brake fluid. Equal-bore 28.575mm pistons maintain even pad pressure distribution across the full friction surface.
AKB (anti-knockback) springs maintain piston position through aggressive cornering, eliminating the pedal drop that occurs when disc runout pushes pistons back into the caliper during high-speed direction changes.
Two-Piece Floating Design
One-piece discs cone when heated unevenly — the center heats faster than the outer edge, causing the disc to warp and create vibration. The two-piece floating design with 10-bolt attachment and oblong hat mounting holes allows radial expansion without distortion.
Five anti-knockback spring clips per disc maintain ring position on the hat, preventing rattle and ensuring the disc returns to center after thermal cycling.
J Hook Slot Pattern
Straight slots create localized cool spots and stress risers that can lead to cracking. AP Racing's J Hook pattern creates a constant pathway of evenly distorted material across the entire disc face.
The result is uniform heat distribution, cleaner pad transfer film, and more leading edges per rotation for consistent bite from the first lap to the last.
How It Compares
Essex/AP Racing vs. OE E46 M3 Rear
| Specification | Essex CP8350 | OE E46 M3 Rear |
|---|---|---|
| Type | 4-Piston Fixed Superior | 1-Piston Sliding |
| Weight (no pads) | 4.8 lbs 37% Lighter | 7.65 lbs |
| Piston Count | 4 4x More | 1 |
| Finish | Hard Anodized Track Grade | Paint |
| Specification | Essex/AP Disc | OE E46 M3 Rear |
|---|---|---|
| Type | 2-Piece Floating Superior | 1-Piece Solid |
| Weight | 15.93 lbs | 14.94 lbs |
| Diameter | 325mm | 328mm |
| Thickness | 32mm 60% Thicker | 20mm |
| Internal Vanes | 70 Directional 133% More | 30 |
Pad Compatibility
D50 Pad Options
This kit uses D50 shape pads (FRP3116 series) — 133.2 x 60.0 x 20.0mm
| Pad Compound | Series | Price | Recommended Use |
|---|---|---|---|
| Ferodo DS2500 | FRP3116H | +$125 | Dual-purpose street / light track — excellent cold bite |
| Ferodo DS1.11 | FRP3116W | +$125 | Versatile track compound — wide operating range, consistent feel |
| Ferodo DS3000 | FRP3116 | +$125 | Aggressive track compound — high friction, linear response |
| Ferodo DSUNO | FRP3116 | +$125 | High-performance track — strong initial bite with excellent modulation |
| Ferodo DS3.12 | FRP3116G | +$125 | Maximum aggression — endurance and heavy competition |
Fitment
Compatible Vehicles
Wheel Fitment
Clearance & Resources
Gallery
Product & Install Images
Spare Parts
Replacement Components
Individual replacement parts available for long-term serviceability
Critical Warning
Parking brake removal: This kit REMOVES the OE cable-actuated parking brake. Your vehicle will have no mechanical parking brake after installation. This kit is designed for track-focused vehicles using a hydraulic handbrake or alternate parking solution.
Not recommended for daily drivers that rely on the parking brake for hill parking or state inspection requirements.
Brake balance: If upgrading rear only (unusual), ensure front braking capacity is sufficient. This kit is typically paired with a front big brake kit for balanced performance.
Pro Tips
Brake fluid: Use high-temp racing brake fluid (DOT 4+ minimum). Bleed the entire rear system thoroughly after installation.
New disc prep: Discs have a rust-prevention coating — wash with soap and water before installation.
Disc sides are handed: CP3870-138GC is the right disc and CP3870-139GC is the left disc. They cannot be swapped side-to-side.
Pad bedding: Follow proper pad bedding procedure for your selected compound before any aggressive track use.
Professional Installation
Function Factory Performance offers professional brake service and installation for all AP Racing by Essex brake systems.
Located in Thousand Oaks, California, serving BMWs, Mustangs, Corvettes, McLarens, and more.
Phone: (805) 206-2523
Lifetime Support
Caliper Reconditioning Program
Built to Last — Backed for Life
Essex is AP Racing's official North American caliper reconditioning center. When your calipers need servicing after years of hard use, Essex can restore them to factory specification for approximately $155–160 per caliper.
This is not a warranty service — it is a testament to the quality of AP Racing's manufacturing that calipers can be rebuilt and returned to active competition rather than discarded.
Expert Guidance
Questions About Big Brake Kits?
Our brake specialists can help you choose the right kit, pad compound, and supporting modifications for your E46 M3 track build.
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