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How to Install a GT/CS (California Special) Spoiler on your 2010-2014 Mustang

Installation Time

2 hours

Tools Required
  • 1x Philips-Head Screwdriver
  • 1x Flat-Head Screwdriver
  • 1x Scissors 1x Roll of Blue Painter’s Tape 10mm Deep Docket Wrench
  • A Power Drill**
  • ¼" Drill Bit** 1x Pen/Pencil** 1x Plastic Spatula** Additional Tools Recommended: Microfiber Cloth
  • 3x more screwdrivers Your favorite Quick Detailer** Your favorite Polishing Compound**
  • 5/32" Drill Bit**
  • ½" Drill Bit**
American Muscle
Shop Parts in this Guide



The following installation will take roughly 2 hours from start to finish provided you have all of the required tools. The installation will be divided into roughly 5 sections as outlined below.


1. Removing Trunk Cover

2. Stock Spoiler Removal

3. Creating the Template

4. Drilling the Holes

5. Installation of New Spoiler

1. Start by making sure your car is parked and the emergency brake is engaged.

2. Using your key or remote control, open the trunk of your Mustang.    

3. Notice that there are 13 pins holding in the trunk cover to the decklid. 2 of the 13 pins will be held in the top of the decklid. These 13 pins (circled in yellow above) need to be removed. In order to remove these pins, you can use your fingernail or a flathead screw driver to pop the center out.    

4. Pull the center pin out and this will allow you to pull out the pin holder. You will need to pull out the pin in order to pull out the pin holder. Pull out all 13 and keep them in a safe place.    

5. Once all 13 Pins have been removed you can remove you trunk cover and put it in a safe location. I chose to rest mine in my trunk since I knew I wouldn’t be storing anything in there.    

Stock Spoiler Removal (If your car has one; If not skip to Step 15)

6. Now that the trunk cover has been removed from the bottom of the decklid, you can begin the process for removing the stock spoiler. The stock spoiler is held on by 4 nuts and 3M tape. The four nuts locations are highlighted in red below.    

7. The two inner nuts are easily identified and accessible from the factory. The two outer nuts (far left and far right are covered by plastic stoppers. These can be lifted out by using your fingernail or Philips-head screwdriver.    

Inner Nuts (Left Side pictured above)

8. After removing the stoppers, all 4 nuts will be exposed (highlighted again in red below) and can be removed using your 10mm deep socket wrench. Put these nuts in a bag and keep them where you will store your stock spoiler.    

9. Not that the stock spoiler has been unbolted from the trunk lid, there is an immense amount of 3M tape seal all sides of the spoiler with a large portion surrounding the 2 outer bolts. You can see the 3M tape in greyish white in the image below holding the spoiler to the decklid. This needs to be removed in order to remove the spoiler.    

10. In order to protect the integrity of the paint on the decklid and the spoiler, line the decklid where the spoiler meets with blue painters tape. *Remember the spoiler does not attach to the quarter panel, therefore there is no 3M tape holding the spoiler to the quarter panel.    

11. Using your plastic spatula, wedge it between the spoiler and the body in order to begin splitting the 3M tape, gently lifting the spoiler all along as you split the tape. It may be difficult at first but it will eventually start to split. ***NOTE: Remember, when handling this part, be gentle as you are working with a surface of your car that WILL be exposed with the GT/CS spoiler. Under NO circumstance should you use a metal edged tool, this will destroy the paint and can cause irreparable damage.

12. Once all of the 3M tape has been loosened, you can set your stock spoiler aside. Take a look at the bottom of the spoiler and the decklid and you can appreciate what FORD did to secure the spoiler from the factory.    

13. There will be a large amount of 3M tape remaining on the decklid. First use, your Quick Detailer and the microfiber cloth to remove the tape residue that will come off easily. In order to get the remainder of the 3M tape off you can use two methods. Method 1: Good old fashioned thumb rolling. Method 2: Using GooGone (or any other variant). I went with thumb rolling since I wanted to do as little damage to my paint as possible.    

14. I also recommend using a polishing compound to remove remaining residue and finally any micro scratches or swirling that could be on the car. It will become much more difficult when the spoiler has been installed.

Before Polishing

After Polishing

Creating the Template (the template should be created whether you have a stock spoiler or no spoiler)

15. If you haven’t noticed already, the GT/CS Spoiler has 8 bolts. If you can recall, the stock spoiler has 4 bolts. You will be required to drill 4 additional holes in order to install the GT/CS Spoiler. Start creating your spoiler by cutting the top of the box that your spoiler was shipped in and lay it out in an open space.    

16. Cut out a half-circle from the center and a small cube from the upper right corner. Using these large cutouts will allow you to roughly fit the cardboard template to the top of the decklid around the decklid bump and the AM/FM antenna.    

17. Move the edge of the cardboard off of the trunk and use a screw driver to puncture a hole in the cardboard in the relative location of the hole in the trunk lid. After poking the hole, lift and place the screw driver into the hole to roughly secure the template. ***NOTE: Whenever handling metal tools near the surface of your paint, use extra caution.    

18. Using your extra screwdrivers, perform the same method with the remaining 3 holes on the decklid. NOTE: Once again, exercise caution using metal tools near your paint.    

19. Put the remainder of your shipping box on the open space on the floor and gently lay your new spoiler on the cardboard upside down.    

20. Using your rectangle that you cut out for the AM/FM antenna, line the template up with the appropriate orientation. After lining up the template, use 4 of the supplied bolts to ensure fitment of the 4 pre-fit rear bolts on the spoiler by pushing them through the cardboard holes you just created. (Yellow, below) You can also use this opportunity to ensure threading goes all the way down.    

21. Using a screwdriver, gently locate the location of the other four nut locations on the spoiler and use the remaining four bolts to fit the cardboard template.    

22. Using a Pen, circle the holes so that you know which holes are the correct holes (this is done in case you needed to poke several holes before finding the correct nuts in the spoiler.    

23. Remember, because the spoiler is upside-down, you just marked the bottom of the template (note the orientation of the rectangle for the location of the AM/FM antenna). Flip it upside and using the foam gaskets provided by AmericanMuscle, mark and trace the top of the template. (Once again note the orientation of the rectangle to be sure to locate the holes properly).    

24. Trace the gaskets and congratulations, your template for drilling the holes is complete.    

Drilling the Holes

25. In order to protect the paint on your trunk decklid, use the blue painters tape to cover the stock drilled holes and the approximate location of where the new holes will be located. Use your template to estimate locations.    

26. Use your template and the 4 screwdrivers to poke holes back into the blue tape in the locations of the stock holes. ***NOTE: Whenever handling metal tools near the surface of your paint, use extra caution.   

27. Using a pen or marker, mark the location where the new holes will be using the template. ***NOTE: Be sure that where you are marking with your pen, you see blue painters tape so that you don’t mark or scratch your paint.  

28. After marking all 4 new bolt holes, remove the screwdrivers and template from the car. You should be able to easily distinguish where you will be drilling on the trunk decklid. Put the gasket on the trunk decklid and make sure that the hole locations line up with the holes in the gaskets (which should also, naturally, match the GT/CS Spoiler).    

NOTE: Do not remove the painters tape until all drilling is complete. The painters tape ensures that the paint holes to the car during drilling.

NOTE: The following steps are IRREVERSIBLE and should be handled with care. If you do not have experience using a power drill, please consult someone who is a professional.

29. Using the 5/32” drill bit in your power drill, gently and controllably drill a hole through each of the marks that you marked on the painters tape.    

30. While drilling through the decklid, once the bit pierces through the metal, the bit will slide in until it hits another sheet of metal roughly ¼” into the decklid. This is because the decklid is actually comprised of two sheets of metal. You will need to drill through the second sheet as well in order for the provide bolts to reach the nut on the spoiler. Below are pictures of the inner holes (below-left) and the outer holes (below-right).    

31. Using the ¼” drill bit drill all four holes (outer through inner). This is size of the 4 bolts and will allow them to pass through the decklid. Below is an example of one of the holes from the inside.    

32. At this point you have two options. Option 1: Purchase 4 longer bolts which can reach through the first layer and second layer to tighten into the GT/CS Spoiler. Option 2: You can use a ½” drill bit ONLY on the inside sheet layer on metal. This will allow the bolt head and washer to slip through the inner layer to tighter against the outer (trunk surface) layer of the car.

I chose to go with Option 2. I wanted to use the parts that came with the spoiler. Be careful when choosing option 2. Anyone who has dealt with larger drill bits knows they have a tendency to get away from the handler and you do NOT want the bit to go through the outer surface of the trunk.

33. With the hole drilling complete, lift your spoiler and mock hold it in place to ensure all your holes line up. If you took extra time to create your template and didn’t rush, they should like up perfectly.

34. After confirming that the holes are correct, gently lay your spoiler on the cardboard and gather your rubber gaskets. Peel the white side off the gasket and apply the sticky side to the spoiler.        

35. Lift the spoiler into place and screw all 8 bolts into the spoiler. Lightly tighten each bolt without completely tightening the spoiler down until all 8 bolts have been fitted. After all 8 bolts are fitted, alternate tightening them down.

Congratulations!!! Your GT/CS (California Special) Spoiler has now been installed. Before After Installation Guide

   Installation Guide Written By AmericanMuscle Customer Stephen Lonison 5/17/2013  

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