erably less compliant than the stock rubber
IRS subframe bushings. These stiffer bushings
virtually eliminate displacement of the IRS subframe
relative to the chassis, thus improving stability and
predictability of the car during acceleration, braking
and cornering. The polyurethane still provides very
good noise isolation. 1979-98 cars fitted with IRS
require MMIRSU-2 bushing kit.
Note: MM has developed a Bushing Removal
Tool (MMT-6) to aid in the fast removal of the
stock rubber IRS subframe bushings. Not only
does this tool reduce the time spent on this job
by at least an hour, it also makes bushing re-
moval much easier.
Note: Installation of this kit requires 6 jackstands,
a floor jack, a hand drill, and an assortment of
common hand tools.
1. Block the front wheels of the car.
2. Raise the rear of the car with a jack and support
the rear of the car on a pair of jackstands. This
first pair of jackstands MUST be positioned under
the chassis of the car (e.g., under aftermarket
subframe connectors or under the torque boxes),
not under the IRS subframe.
3. Remove the rear wheels.
4. Remove the cat-back exhaust system.
5. Position the jack under the differential and raise
the jack until it just contacts the differential. Do
not lift the rear of the car off the jackstands.
6. Position a second set of jackstands 3 inches
under the main rear tube of the IRS subframe.
The main rear tube of the IRS subframe is
located just forward of the gas tank.
7. Remove the two rear 12mm IRS subframe
mounting bolts.
8. Slowly lower the rear of the IRS subframe onto
the second pair of jackstands. 2005.11.08 Copyright 2005
2
MMIRSU-1r4.pmd
Note: If you have an MMT-6 Bushing Removal Tool,
remove the two rear rubber bushings with the
tool now. If you do not thave the tool, use the
procedure detailed in Step 9 to remove the rubber
bushings.
9. Remove the two rear rubber IRS subframe
bushings from their respective shell by walking
a 5/16 drill bit around the interface between the
bushing and the shell. To walk the drill bit, place
the tip of the drill bit in the interface between the
bushing and the shell. When the drill is turned
on, the drill bit will have a tendency to walk
around the perimeter of the bushing, thereby
cutting the bushing from the shell. As needed,
gently push the drill bit deeper and deeper into
the bushing while encouraging the bit to walk
around the bushing. Continue until you have cut
all the way around the bushing, from the front
face of the bushing to its rear face.
10. After removing the two rear rubber bushings from
the shells, it is essential to remove ALL of the
rubber that is still bonded to the interior surface of
the shells and to sand the interior surface of the
shells until SMOOTH. A drill or die grinder with a
sanding roll works well.
11.Apply a thin layer of the supplied grease on the
interior surface of each shell and to the exterior
surface of two MM Polyurethane IRS Subframe
Bushings.
12. Insert one Polyurethane IRS Subframe Bushing
into each shell. Insert the bushing into the shell
from the side facing the gas tank. Do NOT use
excessive force to insert the bushings. If exces-
sive force is necessary, additional sanding of the
interior surface of the shell is required. The
bushing is fully inserted when the shoulder at the
end of the bushing is flush against the lip of the
shell.
13. Note the different ID of the Steel Crush Tubes.
One pair has a large 14mm ID and one pair has
a small 12mm ID. Select the pair of crush tubes
with the small 12mm ID. Apply a thin layer of the
supplied grease on the interior surface of the
hole in each installed Polyurethane IRS
Subframe Bushing and to the outer surface of
each 12mm ID Steel Crush Tube.
14. Insert a 12mm ID Steel Crush Tube through the
hole in each installed Polyurethane IRS
Subframe Bushing.
Do NOT re-attach the rear of the IRS subframe
to the chassis yet. You need to leave the rear of
the IRS subframe on the jackstands to have
sufficient clearance around the fuel tank to lower
the front of the IRS subframe. MMIRSU-1r4.pmd
3 Copyright 2005

2005.11.08
15. Place the jack under one of the jacking pads of
the IRS subframe (i.e., just rearward of where
the front of the IRS subframe attaches to the
chassis) and raise the jack until it comes into
contact with the jacking pad of the IRS
subframe. Do not lift the rear of the car or the
IRS subframe off the jackstands.
16. Position a third set of jackstands 3 inches under
each of the front legs of the IRS subframe just
behind the jacking pads.
17. Remove the two front IRS subframe mounting
bolts. Measure the diameter of the bolt threads.
These two bolts should be 14mm in diameter. In
some cases an incorrect 12mm bolt was in-
stalled in some Cobras on the Ford assembly
line. This was especially common on 2003 and
later Cobras. If your car has the incorrect 12mm
bolts you may purchase the correct 14mm bolts
and 14mm nuts from your local Ford dealer, or
from Maximum Motorsports. MM stocks the
OEM Ford bolts for this application. Do NOT re-
use 12mm bolts, as they are incorrect. The
correct 14mm bolts are needed to properly
locate and secure the subframe.
18. Slowly lower the front of the IRS subframe onto
the jackstands.
Note: If you have an MMT-6 Bushing Removal Tool,
remove the two front rubber bushings with the
tool now. If you do not thave the tool, use the
procedure detailed in Step 9 to remove the rubber
bushings.
19. Remove the two front rubber IRS subframe
bushings from their respective shell using the
technique described in Step 9.
20. After removing the two front rubber bushings
from the shells, it is essential to remove ALL of
the rubber that is still bonded to the interior
surface of the shells and to sand the interior
surface of the shells until SMOOTH. A drill or die
grinder with a sanding roll works well.
21. Apply a thin layer of the supplied grease on the
interior surface of each shell and to the exterior
surface of each remaining MM Polyurethane IRS
Subframe Bushing.
22. Insert each bushing into the shell from the side of
the shell facing the driveshaft. Do NOT use
excessive force to insert the bushings. If exces-
sive force is necessary, additional sanding of the
interior surface of the shell is required. The
bushing is fully inserted when the shoulder at the
end of the bushing is flush against the lip of the
shell.
23. Apply a thin layer of the supplied grease on the
interior surface of the hole in each installed
Polyurethane IRS Subframe Bushing and to the
outer surface of each 14mm ID Steel Crush
Tube.
24. Insert a 14mm Steel Crush Tube through the hole
in each installed Polyurethane IRS Subframe
Bushing.
25. Raise the front of the IRS subframe into position
and re-install the two front 14mm subframe
mounting bolts. If the car is equipped with con-
ventional rear coil springs, make sure they are
positioned properly on the spring perches as the
front of the IRS subframe is lifted into place.
26. Raise the rear of the IRS subframe into position
and re-install the two rear 12mm subframe
mounting bolts. 2005.11.08 Copyright 2005
4
MMIRSU-1r4.pmd
27. Torque each of the four IRS subframe mounting
bolts to 76 ft-lb.
28. Re-install the cat-back exhaust system.
29. Re-install the rear wheels. Torque the lug nuts to
the appropriate vehicle or wheel manufacturers
specifications.
30. Lower the rear of the car to the ground.
31. Test drive the car. Be sure to get acquainted with
the improved driving characteristics of the car
prior to engaging in spirited driving.
32. Re-torque the four subframe mounting bolts after
1000 miles of driving.
This kit includes the following:
4
Polyurethane IRS Subframe Bushing
2
12mm ID Steel Crush Tube
2
14mm ID Steel Crush Tube
2
Grease Packet