2 3 4 5 6 7 8

by Richard Cordon III

So you've added a Cold Air Intake and tuned the Power Train Control Module (PCM) to help wake-up your 2005-2009 Mustang (S197), but you’re still looking for that something to help get rid of that annoying hesitation off-the-line. Well the guys at RatStang Restoration have taken on the problem of hesitation by replacing their 2005 Mustang's factory 3.37:1 rear gear ratio with a 4.10:1 ring and pinion

In this article, Richard Cordon and RatStang Restoration will be performing their gear swap in typical "garage" fashion with common hand tools. The RatStang team will drop the rear axle assembly out of the '05 and take you by the hand and lead you step-by-step through the axle drop, gear swap, gear setup, and reinstallation of the Ford 8.8 back into their Mustang. Once the operation is complete, the S197 will jump right into its finely-tuned torque band for a no-hesitation launch leaving the competition wondering what happened.

Choosing the Gear Ratio
To begin, RatStang Restoration needed to decide what gear ratio they were going to use. The subject S197 came equipped with the 5R55S automatic transmission. In the already mildly modified S197, the torque band had been tuned to the lowest RPM possible with PCM tuning. In its present the state the torque band comes alive at 2000 RPM and takes off from there. Knowing this, they needed to launch into the torque band right off the line. So, at 1300 RPM they are starting their roll; but the torque band comes in at 2000 RPM. So between 1300 RPM and 2000 RPM there is a hesitation until the torque grabs hold. Using the information they gathered and one of the many calculators on the web, RatStang decided on a 4.10:1 rear gear ratio. This ratio would place them right around the targeted 2000 RPM when they begin to roll off the line.

For this swap Ratstang chose Ford Racing Gears as the replacement due to their reputation and ease of installation. Additionally, the team chose Summit Racing’s installation kit due to the completeness of the kit for this project. Are you ready? Let's get started with the Ratstang process.

Dropping the Axle

1. Board the front tires and place the jackstands in the factory jacking locations, located just in front of the rear tire. Refer to vehicle manual for jacking locations and information.
2. Never work under a car that is supported by only a jack. Jackstands or a vehicle lift is absolutely required for this project!

3. Once the car has been securely placed on jack stands, pull the lug cover, loosen the lugs, and raise the rear end using a jack, and finish removing the wheels.
4. Once removed, you now have access to start removing the parking brake cable.

5. First remove the cable retaining clip.
6. Then grab the cable and pull down and toward the axle to remove it from the parking brake bracket.

7. To remove the cable, just rotate the end...
8. ... and slide the end out.

9. We will now loosen the 12mm Speed Sensor retainer bolt.
10. Remove the speed sensor bolt.

11. Now we will use a screw driver between the disc and dust shield to lightly pry on the face of the speed sensor.
12. As you lightly pry, grab the speed sensor and jiggle it loose, being careful not to damage it.

13. Remove the speed sensor cable retaining clip from the caliper bracket, and place the speed sensor aside... out of harms way.
14. Next we will remove the brake calipers. We'll start by removing the caliper's 15mm upper mounting bolts.

15. Then while holding the caliper with one hand, remove the caliper's 15mm lower mounting bolts.
16. Once the bolts have been removed, remove the caliper from the disk.

17. We'll hang the caliper out of the way. We hung it on the axle bumper location using some parts hanging wire.
18. Next we will begin removing the Panhard rod bolt cover. There is a clip retaining the cover located right above the driver side lower trailing arm mounting location.

19. Using a screw driver we will lightly compress the clip being careful not to damage it as we lightly lift and pull the cover from the axle.
20. Remove the cover and place aside.

21. Here is a shot of the clip, just so you have a better idea of what you're working with.
22. Using a breaker bar, we will break loose the torque on the 18mm lower panhard rod bolt.

23. We will now remove the lower panhard rod bolt and flag nut.
The axle will need to be moved later to get the panhard rod out of the mounting location so we can secure it out of the way.
24. We moved on to removing the rear sway bar. Remove the 15mm lower rear sway bar bolts located under the shock absorber...

25. ...on each side of the axle housing.
26. Now remove the nuts and retaining brackets. Pull the sway bar out and place the bracket back on and finger tighten the nuts for convenience.

27. Remove the 15mm upper sway bar bolts.
28. Now remove the sway bar from the vehicle and place it out of the way.

29. Loosen and remove the 15mm lower shock absorber bolts.
30. Pull the shock absorber out of the way. Replace and finger tighten the shock absorber bolts for convenience.

(Dropping the Axle Continued)

2 3 4 5 6 7 8

In This Article...
No step goes un-photographed in this 8-page reference guide for changing the rear gear in your 2005-2009 Mustang.

About RatStang Restoration
The information in this article was contributed by FordMuscle member Richard Cordon (FM username Ixtlan) of RatStang Restoration. Richard operates a small restoration business from his home specializing in full body restorations.

Contact Information:

RatStang Restoration
Richard Cordon III
Northern Utah

Other articles by Richard Cordon:
Torque Boxes:
1965-1970 Mustang

Installing Floor Supports:
1965-1970 Mustang

Installing Subframe Connectors: 1965-1970 Mustang


Tech Archives Project Cars Readers Cars Feature Cars