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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.

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

Ford Racing IRS differential cover, modified by MM, 1999-2004 Cobra
Actual product may differ from photo.
  • Ford Racing IRS differential cover, modified by MM, 1999-2004 Cobra

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  • Item # MAX-4033


Read about the installation on

High-strength FRPP differential cover for the Cobra IRS, modified by Maximum Motorsports to provide clearance for use with the MM aluminum differential mounts.

  • This FRPP cover is an excellent upgrade for the Cobra IRS, offering greatly increased strength over the stock cover.
  • Has clearance to allow installing the MM aluminum differential mounts. The pinion-adjustment ability of the MM aluminum mounts lowers the differential cover relative to the IRS subframe cradle, which would cause the FRPP cover to interfere with the cradle unless the cover is machined to provide clearance.
  • Includes load bolts to support the bearing caps.
  • Offers the convenience of ports for draining, filling, and sensors.
  • Includes provision for oil cooler lines.
  • Unlike some aftermarket covers, includes OEM-quality internal oil baffle at the vent.
  • Much thicker than the stock cover, for increased strength. Stock covers are a well-known weakness of the Cobra IRS. This cover provides increased strength without the need for an additional brace.
  • Reduces the possibility of cover breakage or oil leaks.
  • Modified by MM to install along with MM aluminum differential mounts that allow adjusting pinion angle.
  • May be installed with stock rubber mounts and direct replacement urethane mounts.
  • Load bolts provide additional support for the differential bearing main caps.
  • Separate ports for draining, filling, and checking the level make servicing much easier.
  • Includes provisions for oil cooler inlet and outlet.
  • Easily drilled and tapped for a temperature sensor.
  • Machined groove on mounting surface captures silicone sealant to form a better seal.
  • Direct replacement FRPP design fits like an OE part should.
  • Thick, high-strength aluminum casting provides far greater strength than the breakage-prone stock cover.
  • Precision-machined recesses for clearance to IRS cradle when installed along with MM aluminum differential mounts.
  • Load bolts
  • 10 attachment bolts and washers
  • Machined groove on sealing surface


  • 1999-2004 Mustang Cobra IRS
  • MM aluminum differential mounts that lower the differential cover
  • Stock rubber differential mounts
  • Direct replacement urethane differential mounts

Why does the stock differential cover break?
The primary cause of cover breakage is the impact loads during wheel hop. The stock rubber bushings allow the center section to flop around violently, which can easily break the thin stock cover. Aluminum differential bushings prevent movement of the center section, greatly reducing the possibility of cover breakage. A stronger cover such as the FRPP cover is an added layer of insurance against cover breakage.