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How to Install Full Tilt Boogie Rear IRS Differential Mount Bushings (99-04 Cobra) on your Ford Mustang

Tools Required
  • Jack and Jack Stands
  • Metric Sockets: 12,13,15,18,21mm
  • Extensions
  • 12pt 12mm Socket
  • T40 Torx Bit
  • Flathead Screw Driver
  • Pry Bar
  • Tie Rod Puller
  • Vice Grip Pliers
  • Channel Lock Pliers
  • WD-40
  • Lug Wrench
  • Torque Wrench
  • MM or FTBR IRS Differential Rear Mount Bushing Removal Tool
  • Blue Loctite
  • Extra Set of Hands (Optional)
  • Impact Wrench (Optional)

Note: All bolt IRS bolt and head sizes as well as torque specs are listed on the last page for reference. It is highly recommended to use blue Loctite on all bolts that have a used nylon lock nut.

Note: It is HIGHLY recommended that both the front and rear differential mounts are replaced, not just one or the other. If only one set is addressed, it places extra stress on the differential due to how much give the stock bushings have and can potentially do more harm than good.

This install can be done with the IRS out of the car, but I’ll describe how to do it with the IRS still in the car and just by dropping the differential. Both methods work just as well. Also, keep in mind that the differential is around 65lbs, so be careful!

Install

1. Chock the front wheels of the car. 

2. Raise the rear of the car with a jack and support it with a set of jackstands.


3. Loosen the rear lugs and remove the rear wheels.

4. Disconnect the catback and remove from hangers (this is where the WD40 and pliers really come in handy).

5. Mark your driveshaft position relative to the pinion and then using a 12pt 12mm socket loosen the driveshaft bolts and tie the driveshaft out of the way. 

6. Remove the e-clip on the ebrake cable with a flathead screwdriver.


7. With a set of vice grips, securely grab onto and pull the end of the cable and use a flathead screwdriver to unhook the cable end from the caliper. (A detailed video on how to do this is on youtube from FTBR, just look up “IRS emergency brake cable removal”).

8. Remove ebrake cables and secure them out of the way.

9. Using a 15mm, loosen and remove the bolts securing the brake caliper brackets to the spindles. Or you can use a ratcheting 12mm wrench to remove the rear calipers from the brackets and then move onto the brackets.

10. Securely tie the brake calipers out of the way so they are not hanging by the brake lines and remove rotors.

11. Remove ABS sensors from the diff housing using a T40 torx bit.

12. Remove cotter pins and remove tie rod end nuts using a 15mm.

13. Remove the tie rods from the knuckles using a tie rod puller.


14. Remove the upper and lower control arm to knuckle bolts and let the halfshaft sit on the lower control arm.

15. Use a pry bar (or large flathead) and carefully pry between the diff housing and halfshaft to pop it out of the differential.


16. Once loose, carefully slide the halfshaft and knuckle assemblies out and place them off to the side. Try not to let them drag on the axle seals. An extra hand helps here.

17. Place a jack under the differential and jack up enough to support it slightly.

18. Remove the two 15mm rear diff cover to diff mount bolts.

19. Remove the two front 15mm differential mount bolts.

20. Loosen the two 21mm nuts holding the IRS crossmember (torque brace) to the subframe and slide it off the bolts.


21. This should free up the differential enough to be removed from the bottom. Carefully lower the rear of differential and remove the differential from the IRS. A second set of hands really helps here. Be careful not to spill diff fluid out the axle holes. It would be a good time to replace diff fluid while it’s out.

22. Remove the 13mm driver side rear tie rod bolt holding it to the frame.


23. Once the driver side tie rod is out of the way you will have access to the 18mm bolt that holds the diff mount to the IRS subframe. Remove this bolt and then slide the diff mount towards the front of the car to remove it.

24. With the diff mount removed, use the diff mount bushing removal tool remove the stock rubber bushing.


25. It is recommended to freeze the delrin bushings overnight to help them slide in easier. If extra force is needed, you may use a press if you have access to one like I did. Or if you flip the shell from in the bushing removal kit upside down and use a deep socket and extension, with the threaded rod/bolt and thick washer it can be used to slide the bushings in. The same can be done with the aluminum inner sleeve.


26. If running the Ford Racing differential cover, you will need to check clearance and may have to shave down the bushing and diff mount slightly to have about an 1/8” clearance.


27. Once the bushings are in, your install is finished and the differential can be installed the same way it came out. (Torque specs below)


Note: The diff mount should be oriented with the bend on the top when installed.



Installation Instructions Written by American Muscle Customer 10/23/2017.