How To Replace 5.0 Resto '93 Cobra Style Brake Booster | 1979-93 Mustang

Created by Jay Walling
Date Created: 10/20/2021
Last Updated: 10/28/2022

Follow along as LMR walks you through all the steps to complete the 1993 Cobra-style brake booster install on your 1979-1993 Fox Body Mustang!

Viewing this install and using the information shared is subject to the terms set forth here - View the LMR Install Instructions Disclaimer.
How To Replace 5.0 Resto

About Our 5.0 Resto 1993 Cobra Style Brake Booster

One of the oldest past times in the long history of hot rodding has been to take other components from different trim levels of vehicles and install them on a lesser-equipped vehicle for an upgrade. Well, this is true for a '93 Cobra-style brake booster. Let’s take a trip back to the 90s; Ford Racing would release one of the best brake kits that there ever was, the M-2300-K brake kit for 87 to 93 Fox Mustangs.

This kit utilized upgraded braking components from the '93 Cobra R and the 94 and 95 Cobras. Amongst those components was the ‘93 Cobra brake booster. As time passed, the M-2300-K brake kit fizzled away into the archives, which forced enthusiasts to piece together their upgraded braking components. So, for years, Fox Mustang owners that installed better braking components would opt for a '93 Cobra booster because of its larger diaphragm, which would provide better pedal assist for upgraded braking systems.

Fast forward to today, 5.0Resto is proud to offer a brand new '93 Cobra-style booster. This booster is a direct fit for '93 Cobras and an upgraded unit for 1979 to 1993 Mustangs. It features a black e-coated finish and shares similar dimensions and tolerances to a factory '93 Cobra brake booster. Unlike other offerings, this is not a remanufactured unit. This is a brand new unit with all new components and pieces throughout. All the mounting studs are 3/8-16 thread pitch, so you can reuse your factory hardware if you choose. The actuator rod has the same inner diameter as the factory unit, which allows the plastic bushing to install right into place. Then this will be positioned over the brake pedal arm inside of the car.

On the engine bay side of the brake booster will be an adjustable brake booster pushrod that utilizes an 8mm wrench on the shaft and a 7mm wrench for the jam nut. Whenever the jam nut is loose, you can easily adjust the rod by hand and then retighten the jam nut. While we're on the topic of brake booster pushrod, it is required that you appropriately adjust this before installing the booster into the car. Failure to correctly set brake booster pushrod length will result in the pushrod being too long, and the brakes will drag, or the pushrod will be too short, which results in a low pedal; both of these situations can be very dangerous.

In typical LMR fashion, we have set aside a dedicated article on brake booster pushrod adjustment, so please check that one out. 5.0Resto’s '93 Cobra-style brake booster accepts popular master cylinders, including the SVO, '93 Cobra, and 94-95 GT master cylinders. In the box will be hardware to secure the master cylinder to the brake booster and new brake light switch hardware.

As we said before, this 5.0Resto '93 Cobra-style booster is designed as a stock replacement for '93 Cobras and an upgraded unit for 79 to 93 cars with upgrading braking systems. Now, when we say upgraded braking systems, we're talking about cars that have been converted to 4-lug rear disc or SN95 style 5-lug setups.

As far as fitment notes are concerned, there are a few. Because of the overall physical size of this booster, it will help if you elongate the holes in the firewall, and for pre-1991 cars, the old M-2300-K instructions state that you may need to “relieve” the inner area of the strut tower. This 5.0Resto ‘93 Cobra-style booster is great, especially since all you have to do when you take it out of the box is adjust the brake booster pushrod and install it on your car! No prep or paint is needed, and we break down the removal and installation steps below.

How To Remove & Install Fox Body Brake Booster

Now, we'll be the first to tell you that installing a ‘93 Cobra-style booster into a Fox Mustang isn’t the most fun thing to do because of the overall physical size of the booster, but it’s one of those things… it is what it is. Also, instead of going down the rabbit hole and explaining the differences between the boosters, this article will be focused on factory booster removal and the ‘93 Cobra-style booster installation. So depending on what you’re doing with your car will dictate how the installation process goes.

You’re either going to be in the middle of upgrading the rotors and calipers, whether it be a 4-lug rear disc or to a 5-lug SN95 set up in the front and rear and installing a new master cylinder, or like us; where everything is already in place and all you’ve been waiting on is a ‘93 Cobra-style booster. Regardless of where you’re at, this article will help provide a very detailed explanation of booster removal and ‘93 Cobra-style booster installation.

For what it’s worth, we will be working with our ‘93 silver hatchback, so a few of these steps will differ depending on the year range of your Fox Mustang.


  1. To remove the factory booster from the car, you’ll need to first lift the driver side of the vehicle to gain access to the 1/2" nut that retains the factory proportioning valve to the strut tower. Reach into the wheel well with a 1/2" socket and wrench to loosen and remove the nut. Let's move inside.
  2. How To Replace 5.0 Resto

  3. Now, there are a few different ways to remove the booster to firewall retaining nuts because of the location of the hardware. You can either use an assortment of tools to remove all (4) of the retaining nuts or remove the lower dash trim so you can insert a long extension and a 9/16" socket. Whichever route you take, we would recommend that you remove the seat for optimal working room.
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  5. Remove all (4) of the retaining nuts.
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  7. Remove the cotter pin and spacer using a small pry bar or flat head screwdriver.
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  9. Remove the brake light switch from the pedal.
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  11. Go ahead and carefully remove the actuator rod from the pedal.
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  13. Inside the engine bay, disconnect the electrical connection on the master cylinder and feed it through towards the fender. We would also take this opportunity to disconnect any other electrical connection or component in this general area and position them out of the way as best you can.
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  15. Carefully remove the check valve from the booster and reposition the hose.
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  17. Locate the 2 master cylinder to brake booster retaining nuts. Loosen and remove both of these nuts with a 9/16" wrench.
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    How To Replace 5.0 Resto

  19. Now that these are loose, work the stud and the locating tab on the factory proportioning valve out of the strut tower.
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  21. Next, carefully and methodically remove the master cylinder from the studs on the booster. Before you tilt the assembly towards the front of the car, ensure the cap is tight on the master cylinder, so brake fluid doesn’t leak out. Go ahead and reposition the master cylinder towards the front of the car.
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  23. Back in the engine bay, bring the booster away from the firewall. Because of the limited space, rotate and shift the booster as needed to free the studs from the firewall and then remove the booster from the car.
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  25. Whenever the booster is removed, take this time to clean the surrounding area.
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  1. Now, we can install the ‘93 Cobra-style booster. Before this happens, you must verify and adjust the brake booster pushrod length. We’ve set aside a separate article for that, so please check it out first and then come back over to this article to finish your install.

  2. Whenever the booster rod is adjusted, we’ll need to modify the vehicle to accept the larger booster. These modifications include elongating the (4) holes in the firewall and clearancing the strut tower. We have also found that removing the bolt securing the clutch cable bracket to the frame rail helps push the cable over when positioning the booster. We recommend that you elongate the holes in the firewall first and then test fit the booster before clearancing the strut tower. For reference purposes, we show a dead blow hammer, but depending on how clearancing is needed, you may need to use something with more emphasis, if you know what I mean. Whatever you do, use all means necessary to ensure that you don’t damage the painted surface.
  3. How To Replace 5.0Resto

  4. Position the booster into place. This particular car here cleared the strut tower, but it did need a little persuasion to get past the holes in the firewall. A couple of light taps to the frontward facing studs helped coax the booster into place.
  5. How To Replace 5.0 Resto

  6. Install the master cylinder onto the studs in the front of the booster.
  7. How To Replace 5.0 Resto

  8. Reposition the factory proportioning valve into the strut tower.
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  10. Use the provided nuts and install them onto the booster. Tighten down both nuts using a 9/16" wrench.
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  12. Reconnect the vacuum line to the check valve on the new booster.
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  14. Reroute and connect any electrical connection or component that was disconnected or repositioned in this area.
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  16. Reinstall the clutch cable bracket if it was relocated and tighten the retaining bolt.
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  18. From within the fender well, reinstall and tighten the retaining nut for the factory proportioning valve.
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  20. Safely lower the vehicle.
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  22. Install the provided bushing into the actuator rod on the new booster.
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  24. Position the actuator rod on the brake pedal.
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  26. Reinstall the brake light switch, spacer, and cotter pin.
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  28. Reinstall the (4), previously removed brake booster to firewall retaining nuts and tighten them down.
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  30. If you removed any interior components, go ahead and reinstall these pieces. Reinstall the driver’s seat and the hardware. At this point, you’re either going to finish the rest of your brake component upgrade and then check everything or go ahead and start the car, move it forward under its own power and make sure the brakes function as they should. After that, you’re good to go!

Alright, folks! You have now successfully installed a ‘93 Cobra-style booster into your Fox Mustang. If, for some reason, you may have a few questions, give us a shout. We’ll be happy to hear from you and, of course, steer you in the right direction.

As always for all things Fox Body, keep it right here with the Real Mustang Enthusiasts,!

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1979-93 Mustang Brake Booster

About the Video

How To Remove & Install 5.0 Resto 1993 Cobra Style Brake Booster (1979-93)

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Published on 2021-09-28
Learning how to remove & install the 5.0 Resto 1993 Cobra style brake booster sounds difficult, but it's actually easier than you may think! Follow along as Landan walks you through all of the steps to complete the 1993 Cobra style brake booster install on your 1979-1993 Fox Body Mustang!

If you still need to adjust your 5.0 Resto 1993 Cobra Brake Booster, or you would like to learn more about it, check the links below!

How To Adjust Your 5.0 Resto 1993 Cobra Brake Booster:
5.0 Resto Cobra Brake Booster Review:

Buy 1993 Cobra Brake Booster:

Check out our SVE 5-Lug Conversion Kits:

Intro | 0:00
Before You Begin! | 1:21
Remove Booster Retaining Nuts & Components | 1:35
Removing The Brake Booster | 2:13
Adjusting The '93 Cobra Brake Booster | 3:13
Modifying For The '93 Cobra Booster | 3:28
Install Brake Booster | 4:07
Reinstall The Master Cylinder | 4:21
Reconnect All Additional Components | 4:44
Final Thoughts | 5:41


#LMR #FoxBody #50Resto

Use of this video is subject to the terms as set forth in our LMR Install Video Disclaimer |
Thumbnail image of the author of this article, Jay Walling.

About the Author

Jay has written content for Late Model Restoration for over 10 years, producing over 120 articles. Jay has an extensive 25-plus-year background in automotive and is a certified Ford Technician. Read more...