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IRS Rear Grip Package - Super Street/Competition, 1999-04 Cobra

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This Grip Box takes the Street IRS Grip Box a step further, enhancing performance to be suitable for competition. Improves handling and reduces wheel hop.


  • Eliminates deflection allowed by stock rubber bushings
  • Greatly reduces wheel hop because there is no bushing deflection
  • Precisely locates the control arms for improved dynamic alignment
  • Handling is greatly improved because there are no unpredictable camber changes caused by bushing deflection
  • NVH and ride comfort virtually unchanged
  • Installation tools included, the key to a hassle-free installation

This Grip Box includes:

  • Urethane Differential Bushings - MMIRSB-45
  • Delrin Upper Control Arm Bushings - MMIRSB-2
  • Delrin Lower Control Arm Bushings - MMIRSB-1
  • Urethane Subframe Bushings - MMIRSU-1 (or MMIRSU-2 for 1979-1998 chassis)
  • IRS Adjustable Complete Tie-Rod Kit - MMIRSTR-2
  • Adjustable Rear Swaybar Endlinks - MMRSB-94
  • Low Profile Subframe Bolts, rear mounts - MMF-1
  • 14MM Subframe Hardware, front mounts - MMF-4 (or MMF-5 for 1979-1998 chassis)
  • Specialty tools and detailed instructions to make the job a breeze

What's different from the MMRG-21 Street Grip Box?

  • The complete adjustable tie-rod kit is substituted for the outer tie-rod end bumpsteer kit.
  • Low profile subframe mounting bolts are added to improve clearance for wide tires.
  • Includes new forward subframe mounting bolts: 14mm for the 1999-2004 chassis, 12mm for the 1979-1998 chassis.
Why do I need to specify the year of my Mustang?
So we can include the correct IRS subframe urethane bushings and attachment hardware.
  • 1999-2004 Mustangs use 14mm bolts to attach the forward end of the IRS subframe to the chassis.
  • 1979-1998 Mustangs use 12mm bolts to attach the forward end of the IRS subframe to the chassis.

IRS Tech
MM delivers on the unfulfilled promises of the stock IRS. Enjoy the track performance and reliability of an MM-equipped Mustang IRS. This rear Grip Box will transform your Cobra into a true high performance automobile, with world-class handling and traction.

Handling is improved and wheel hop reduced by eliminating deflection allowed by the stock rubber control arm bushings. Delrin bushings precisely locate the rear control arms, and maintain rear wheel alignment in a manner that is impossible with the compliant stock rubber bushings. Rubber bushings provide barely adequate suspension control. They cannot accurately position the control arms well enough to achieve maximum performance from the suspension.

Wheel hop is a major complaint about IRS-equipped Mustangs. The un-damped compression of the rubber bushings in the rear suspension is the primary cause of wheel hop. That un-damped movement is amplified by repeated loss of traction. Wheel hop occurs because the rear tires continually oscillate between losing and then regaining traction. The extremely soft stock rubber bushings are the biggest contributor to this oscillation. The rubber compresses easily and then springs back, over and over again. To reduce wheel hop the stock rubber bushings must be eliminated.



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