Solid differential bush BMW M3 M4 F80 F82

The problem

On the M3 and M4 F80 F82, the original differential sits on soft bushes, and above all at the rear on just 1, mounted asymmetrically. Designed primarily for comfort and noise isolation, they quickly reach their limits in dynamic use.

The result on track or during spirited driving: the differential moves in its subframe, the driveshafts take a jolt every time you get back on the throttle, and torque delivery to the road loses precision. You can feel the diff « float » through transitions and when accelerating out — a sensation that reveals a lack of stiffness rather than a lack of power. Put it all together and you get the well-known problem of the right-hand driveshaft failing.

The solution

We have developed a completely redesigned differential mount bush, designed and machined to strengthen the diff-to-chassis connection while retaining the residual isolation essential to the reliability of the whole driveline. It draws on recipes that already work, but with more durable materials better suited to the track:

• Black Delrin (POM-C) to avoid a fully solid aluminium setup
• Anodised aluminium (6061) for durability and a solid seat
• 304L stainless steel for the pin, protecting the Delrin body
• Compatible with a Millway diff riser (1 or 2 possible)
• Replaces the OEM bush

What it changes behind the wheel

• Elimination of unwanted diff movement under torque
• Less pulling and fewer jolts on the driveshafts when getting back on the throttle
• A more direct and healthier feeling of traction, especially on corner exit
• A reliability/performance compromise designed for road AND track use, without sacrificing driveline life

Supplied boxed with grease for fitting the body and pins. No need to drop the subframe or carry out a major heavy job.

At first I didn't believe it, but the feeling under hard acceleration is much healthier and less vague... On the 1st test on my M4 I thought it was a placebo effect, but after testing on 3 other M cars it was real.

— Damien, NGU&Kame