The E60 M5: A Performance Icon with Unique Challenges

The BMW E60 M5 remains a modern classic, powered by the naturally aspirated 5.0L V10 (S85) that revs to 8,250 rpm and produces 500 horsepower. This engine is a masterpiece, but the car’s factory transmission and drivetrain components were often the weakest links—especially when owners began pursuing higher output through tunes, exhausts, and intake modifications. The stock SMG III (Sequential Manual Gearbox) is known for high-pressure pump failures, jerky shifts at low speeds, and a "driven disc" that can wear prematurely under hard use. Even the manual transmission cars face clutch limitations and drivetrain shock loads that can stress differentials and axles.

To truly unlock the E60 M5’s potential and keep it reliable over the long term, targeted upgrades to the transmission and drivetrain are not optional—they are essential. This guide covers the most effective modifications to ensure your power delivery is smooth, your components survive aggressive driving, and your car remains a joy to drive whether on the street or track.

Why Focus on Transmission and Drivetrain Upgrades?

The S85 V10’s high-revving nature produces immense stress on downstream components. Stock parts were designed to handle the factory 500 hp, but any power bump—even a modest one—can expose weaknesses. Key reasons to upgrade include:

  • Preventing Costly Failures: SMG pumps and accumulators are failure-prone. A proactive upgrade or rebuild can save thousands in repair costs and downtime.
  • Improving Shift Quality: The SMG III can be jerky and slow in automatic mode. Upgraded software, clutch packs, and hardware make it crisp and predictable.
  • Handling Increased Torque: Forced induction or stroker builds can push torque past 400 lb-ft, stressing the clutch, driveshaft, and differential.
  • Reducing Drivetrain Loss: Lighter rotating components (flywheel, driveshaft) free up horsepower and improve throttle response.
  • Enhancing Traction: An upgraded limited-slip differential puts power down more effectively, especially on corner exit.

Transmission Upgrades: Maximizing the SMG III or Converting to Manual

The E60 M5 came primarily with the 7-speed SMG III robotized manual. Enthusiasts can either optimize that gearbox or swap in a conventional 6-speed manual. Each path has its own upgrade considerations.

SMG III Reliability & Performance Upgrades

The SMG III’s most notorious issues are the high pressure accumulator (often leaks nitrogen), the pump motor (carbon brush wear), and the clutch actuator. Rather than replacing with OEM parts that fail again, consider these upgrades:

  • SMG Accumulator & Pump Rebuild Kits: Companies like Beisan Systems offer rebuild kits that replace the accumulator bladder and pump seals. This restores shift speed and prevents sudden failure.
  • High-Performance Clutch Pack: The stock clutch is adequate for 500 hp but slips under repeat high-rev launches. Upgraded organic or sintered iron clutches (e.g., from UUC or Spec Clutch) can handle 600+ hp.
  • SMG Software Tuning: Custom ECU tunes (by Evolve Automotive or Dinan) remap shift logic, reducing clutch slip on upshifts and adding faster, firmer shifts. Some also raise the auto-shift redline.
  • Rear Pump Mount Bracket: The SMG pump sits in the engine bay; a reinforced bracket reduces vibration and extends pump life.
  • Manual Conversion (Extreme): For ultimate reliability, swap in a 6-speed manual transmission from a 525d/530d (GS6-53BZ) with adapter kits from Evolve or Kassel Performance. This eliminates SMG electronics and pump failures but requires pedal box, shifter, and clutch master cylinder modifications.

Manual Transmission Upgrades

If you already have a manual E60 M5 (or converted one), focus on clutch and shift feel:

  • Lightweight Flywheel: Dropping from the stock 28 lb dual-mass to an 11 lb single-mass flywheel (e.g., UUC LTW) reduces rotational inertia, allowing the engine to rev more freely. Pair with a sprung hub clutch to reduce gear rattle.
  • Short Shifter Kit: BMW’s factory shifter is long-throw. A short shift kit from Understeer or B&M reduces throws by 30–40% and improves precision.
  • Stainless Steel Clutch Line: Replaces the rubber line for firmer pedal feel and better modulation.
  • Clutch Delay Valve (CDV) Removal: The factory CDV restricts clutch engagement speed; removing it gives more direct control.

Drivetrain Upgrades: Putting Power to the Ground

Beyond the gearbox, the E60 M5’s drivetrain needs reinforcement to handle extra power and torque without wheel hop or failure.

Limited-Slip Differential (LSD)

The open differential with electronic torque vectoring is decent but can’t match a mechanical LSD. Upgraded differentials provide predictable lockup and improve traction in corners and during hard acceleration.

  • Wavetrac Differential: Uses a helical design with a patented axial preload mechanism to maintain torque transfer even when one wheel loses grip. Very popular for street/occasional track use.
  • Quaife ATB (Automatic Torque Biasing): Similar helical design, smooth and low-maintenance. Preferred for daily drivers who want improved traction without aggressive behavior.
  • OS Giken Super Lock LSD: A clutch-pack unit with adjustable preload. Best for dedicated track or drift cars; it can be noisy and require periodic rebuilds.
  • Installation: Most shops can install an LSD into the stock differential housing. Expect $2,000–$3,500 for the diff unit plus labor.

Driveshaft (Propeller Shaft) Upgrades

The stock steel driveshaft is heavy. Replacing it with a carbon fiber driveshaft made by Driveshaft Shop or PST reduces rotating mass by 8–10 lbs, which improves throttle response and reduces drivetrain inertia. The carbon shaft also dampens vibration better than aluminum. It is a direct bolt-on for the E60 M5.

Axles & CV Joints

Stock axles can handle around 550 hp, but beyond that or with sticky tires, they may snap. Heavy-duty axles with upgraded CV joints are available from Evolve and Driveshaft Shop. They use 108mm inner joints with larger bearings and upgraded grease for higher torque capacity.

Subframe Reinforcement & Mounts

The E60 M5 subframe can flex under heavy loads, leading to wheel hop and premature bushing wear.

  • Subframe Mount Inserts (AME/RE:) Fill the voids in the subframe bushings to reduce movement. Cheap and effective.
  • Polyurethane Subframe Bushing Set: Replace the worn rubber bushings with polyurethane for constant rear-end alignment under load. Expect slightly more NVH.
  • Differential Mount Bushing Upgrade: The OEM rubber diff bushing allows too much movement; a poly or solid aluminum bushing keeps the diff properly located, reducing clunking and improving traction.
  • Rear Subframe Reinforcement Plates: Cars with higher mileage can develop stress cracks around the subframe mounting points. Weld-on reinforcement plates from Turner Motorsport prevent this.

Bushings & Chassis Stiffening

Upgraded suspension bushings also contribute to better drivetrain feel:

  • Front Control Arm Bushing (FCAB): Polyurethane or monoball replacements reduce flex during braking and acceleration.
  • Rear Trailing Arm Bushing (RTAB): Stiffer RTABs minimize rear-end steer under power.
  • Chassis Strut Bars: A front strut brace and rear strut bar (e.g., Mason Engineering or M-Performance) tie the suspension towers together, reducing flex.

Installation Considerations & Cost Breakdown

Before purchasing parts, plan the installation carefully. Some upgrades can be done at home with basic tools; others require specialized knowledge or equipment.

  • SMG Pump Rebuild: Moderate difficulty. Involves removing the pump, disassembling and cleaning, replacing seals/accumulator. Many owners do it in a weekend.
  • Clutch and Flywheel Replacement: Requires hoisting the transmission. Labor is 8–12 hours. Budget $800–$1,500 for labor at an independent shop.
  • LSD Install: Professional installation recommended. The differential must be removed from the car, disassembled, shimmed, and the LSD carrier installed. Expect $500–$1,000 labor + new fluid.
  • Driveshaft Swap: Bolt-on, moderate difficulty. Need to support the driveshaft, remove old one, install new. Dual-mass flywheel cars may require a special pilot bearing tool.
  • Subframe work: Welding reinforcement plates requires a skilled welder and dropping the subframe. If you are already replacing bushings, it is a good time to do it.

Always check compatibility with your exact model year (2006-2010). Some early SMG programming differs from later ones. Use reputable parts from companies like Evolve Automotive, Beisan Systems, Turner Motorsport, FCP Euro, and BimmerWorld.

Street Performance & Reliability (Daily Driver)

  • SMG accumulator rebuild + pump brush kit (Beisan)
  • Evolve SMG software tune
  • Wavetrac LSD
  • Poly diff mount bushings
  • Front strut brace

This keeps the SMG alive, makes shifts crisp, and improves traction without excessive NVH.

Track / HPDE (High Performance Driving Events)

  • Manual conversion (if SMG) or upgraded clutch + lightweight flywheel
  • Carbon fiber driveshaft
  • OS Giken LSD with 90-degree ramp plates
  • Heavy-duty axles
  • Full polyurethane bushing set (subframe, diff, control arms)
  • Subframe reinforcement plates
  • Stainless steel brake lines + upgraded brake pads (not drivetrain but necessary)

All-Out Power (Supercharged / Turbo)

  • Manual conversion mandatory (clutch type rated for 700+ hp)
  • Carbon fiber driveshaft
  • Driveshaft Shop 108mm axles
  • Quaife or OS Giken LSD with upgraded output bearings
  • Full subframe reinforcement and solid aluminum bushings
  • Sequential shifter (optional, for extreme builds)

External Resources for Parts & Information

For further reading and purchasing, these sources are trusted within the E60 M5 community:

  • Evolve Automotive – SMG tunes, clutch kits, drivetrain upgrades, and manual conversion parts.
  • Beisan Systems – SMG accumulator and pump rebuild kits, known for OEM-quality solutions.
  • Turner Motorsport – Subframe reinforcement plates, bushings, differential service parts.
  • The Driveshaft Shop – Carbon fiber driveshafts and heavy-duty axles for the E60.
  • Quaife – Limited-slip differentials for BMW 188mm differential.

Conclusion: Building a Reliable Power Delivery System

The BMW E60 M5’s heart is its high-revving V10, but the drivetrain must be bulletproof to enjoy that engine without worry. By addressing the weaknesses of the SMG III or upgrading the manual transmission, and by reinforcing the differential, driveshaft, axles, and chassis, you create a car that can handle serious power and deliver it in a predictable, engaging manner. Whether you drive your M5 daily or carve canyons on weekends, investing in transmission and drivetrain upgrades ensures that the legendary S85 is not just heard—it’s felt through the steering wheel, the seat, and the grin on your face.