MM News

New! MM Technical Services: MM’s Engineering Team will provide setup recommendations specifically tailored for your Mustang. Get help choosing options for a Maximum Grip Box, deciding on coil-over spring rates, selecting a brake master cylinder, and advice on converting your Fox to Hydroboost.

New! Swapping a Coyote into a Fox Mustang? MM's Hydroboost Conversion Kits allow easy installation of a 1996-2004 Mustang Hydroboost power brake assist unit into a 1979-1993 Mustang.

New! Swapping an IRS into your Fox Mustang? MM makes it easier with a brake line kit made just for this conversion. Bolts-in, with no cutting or flaring of brake lines. Designed to fit standard IRS brake hoses.

New! MM now offers a tool for the giant nut securing a Mustang Hydroboost. This MM socket fits the 1-7/8" nut holding the Hydroboost to the firewall mount. Required when changing a Hydroboost unit.

New! MM's billet aluminum Pedal Box Spacer for Fox Mustangs. Replace the breakage-prone OEM plastic spacer when converting to manual brakes or Hydroboost.

Canadians! Please read the latest about ordering from Canada/shipping to Canada.

We've posted the parts list and link to the video of MM's Mustang in /DRIVE Tuner car Shootout

IRS differential mounts, urethane, complete kit, 1999-04 Cobra
Actual product may differ from photo.


  • Item # MMIRSB-45
  • Manufacturer: Maximum Motorsports


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Prevent damage caused by wheel hopwith Maximum Motorsports differential bushings.

  • Urethane bushings prevent rear cover breakage caused by wheel hop.
  • Urethane retains low NVH levels acceptable for daily-driven Cobras.
  • Includes all 3 bushing sets: The 2 front sets and the critical rear bushing.
  • Includes MM-designed tool to easily remove the rear bushing.
  • Retains stock differential location and pinion angle.
  • Adjusting pinion angle may reduce driveline vibrations. MM aluminum mounts allow adjustment of pinion angle.

Wheel Hop Breaks Parts

    • Wheel hop can break the rear differential cover.
    • Wheel hop causes violent movement of the differential.
    • Violent flopping around of the differential can break the differential cover, where it attaches to the rear mount.
    • Violent movement is allowed by the overly compliant stock rubber differential mounting bushings.
    • Stiffer bushings, whether urethane or aluminum, prevent the violent flopping around that breaks differential covers.

  • Unlike many others who offer only the front differential bushings, Maximum Motorsports took the time and effort to analyze the IRS system. The MM Engineering Team realized that all of the differential bushings must be replaced as a complete set.
  • The complete set includes the two front bushings and the essential single rear bushing.
  • If only the front bushings are replaced, and the original rubber rear bushing is left in place, a mismatch in the stiffness of the bushing materials will be created. The more rigid front bushings will deflect less, while the remaining rubber rear bushing will still deflect as much as ever.
  • Damage from wheel hop will still be possible because the rubber rear bushing will deflect and allow the differential to flop around.
  • The mismatch in bushing stiffness will increase the stress on the aluminum front mounting ears of the differential housing. The increased stress can lead to fatigue and stress cracking of the aluminum differential housing.

IRS Mustang Tech: Q&A