Big Brake Swap

Swapping big brakes onto a Fox is nothing new. Most people swap over the front and rear brakes off an sn95 and are done. In my particular case, I had a 94/95 V6/GT booster and master cylinder, 94/95 V6/GT spindles and hubs, and a complete SVO rear brake setup laying around. When I ended up with a set of sn95 Cobra rotors and calipers, I went ahead with my swap.

Front Brakes

Swapping the front brakes is essentially a bolt-on swap with spacers and brake lines. First, remove the stock brake, rotor and spindle. And you might want to take care to not get any brake fluid on painted parts – as it’s harmful to the paint. I wasn’t careful and got fluid all over my a-arm.

One thing to be sure of, don’t do this:

I’ve removed brake lines at least a dozen times before, and aways got away with using my standard Craftsman box-end wrenches. But not this time. I completely rounded off the head of the nut – even vice grips wouldn’t get it off. I ended up cutting the line just behind the nut to get the stock soft line off. I also went out to Sears and bought a new set of flare wrenches.

I ended up having to buy a new nut, which took forever to find (Autozone, O’Reilly’s, NAPA, another Autozone, Ford Dealership, and finally found it at Pep Boys), and a flare tool. I bought a Pro Form tool, which broke on the 3rd test fitting – so I don’t think I’ll be recommending that brand tool to anyone anytime soon.

The only trick to fitting the sn95 spindle is the ball joint – the stock Fox stud is too tall. The good solution is to press in a set of sn95 ball joints and be done. Or better yet, some of the trick Steeda X2 or Ford ball joints. Because I needed to keep the stock ball joint, I took the castle nut, drove down to the local hardware store and picked up about $8 worth of spacers in assorted thicknesses. Simply use the spacers to set the castle nut high enough that the cotter pin can hold it in place.

For the brake lines, I picked up a set of braided lines. But be aware that the Cobra calipers changed the thread pattern in 2002. If you have well stocked parts stores nearby, you can take the stock Fox soft line and the stock sn95 soft line to the parts store and find an adapter. Many do this and it works fine. I, however, have poor luck finding supplies at the local stores, and also didn’t have a set of stock sn95 soft lines as they were butchered in their removal from the donor vehicle.

Rear Brakes

The rear brakes were a bit more work, but weren’t really that big a deal. Again, the first step is to remove the stock fox drum brakes, and also remove the axles and backing plates.

To take out the axles, you’ll need to remove the diff cover, take out the center pin retaining bolt and center pin, push each axle in slightly so that you can get to the C clip. After removing the C clip, the axles can be pulled out.

Diff Cover Removed Pinion Shaft and Pinion Shaft Lock Fastener Axle in Place Axle Pushed in Revealing 'C' Clip

After the stock axles are removed, you can remove the backing plates from the ends of the axle housing, then install the SVO backing plates and axles. The axles go back in the same way they came out.

After you have the new axles in place, you can bolt up the diff cover (be sure to clean it thoroughly and use a gasket and/or some sealant), and fill it with fluid.

Now we get past the bolt-on stage, but it’s nothing at all that difficult. The stock fox hard lines will need to be shortened and attached to the SVO soft lines. The SVO soft lines’ bracket bolts to the lower control arm bracket on the axle housing. Some housings have the holes already drilled, but mine did not, so I positioned the bracket on the axle and marked my hole. I drilled and tapped the hole, so that the soft line bracket can be easily bolted and unbolted to the axle housing.

Once the soft lines are bolted to the axles, you’ll get a good idea of where to cut the stock fox hard lines. Again, you’ll need to break out your flare tool. I cut my hard lines just a little longer than they needed to be. The hard lines are soft enough that they can be tweaked to get it all lined up. By leaving a little extra line, I gave myself a little cushion in case I screwed up the double flare. After cutting the hard lines, be sure to slip on the flare nuts before flaring the line. After you flare it, you should be able to attach the hard lines to the soft line at the soft line bracket.

After attaching the hard lines, I then mounted the rotor and caliper, and attached the soft line to the caliper.

If you take your time, everything should come out pretty clean and factory looking.

Master Cylinder, Booster, and Proportioning Valve

The first thing you have to do is remove the stock booster and master cylinder. I climbed under the dash, removed the booster arm from the brake pedal, then the bolts that hold the booster to the firewall. The same bolts that hold the booster are the same ones that hold the pedal assembly in. Be ready to spend a little time getting the wrenches up in there, because things are tight.

After the stock booster and master assembly is out of the way, it’s a good time to gut the stock proportioning valve. Because of the changes in front and rear brakes, and the master cylinder, the stock proportioning valve can no longer be used. Ford has a plug, part number M-2450-A that can be used for this purpose. I removed the stock plug, and all associated components, and plugged the opening with the new Ford plug.

The later Fox Mustangs use a 3 port master cylinder, where one port goes to the rear brakes and then a separate port to the right front and left front. Early Fox master cylinders and the sn95s use a 2 port design, where there is one port for the front brakes and the other for the rear. For the conversion I used the $25 part and instructions from The only problem I had was that the adapter was supposed to fit tight with the line coming out the rear of the adapter at no greater an angle than 15 degrees. Mine simply wasn’t tight enough at that angle, so ended up a bit more – but everything worked just fine.

There are plenty of places around the ‘net talking about installing the huge sn95 booster into a fox. People have found that if you drill out the top left (when facing the firewall) bolt hole, you can slide the booster in without having the beat on the strut tower. I did a little of both; I drilled out the hole a bit, and then “clearanced” the strut tower with a BFH. It takes a little patience, but if you’re expecting a tedious job, it isn’t so bad. To make things a little easier on myself, I also removed the windshield wiper motor, and pulled the wires and loom as out of the way as I could get them.

After getting the booster and master cylinder in, time to move back under the dash to reattach the booster rod and brake switch. When reattaching the brake pedal to the new booster rod, there have been some reports of the brake light switch interfering with some of the under-dash bracketry. I had this same problem. The solution is to use a sn95 connector on the end of the switch, but in a pinch you can remove the connector and bend the tabs over. This worked just find for me.

When it comes to installing a new proportioning valve, this has to be the easiest part of the job. On the passenger’s side of the firewall is a simple butt connector on the brake line. I removed it, and in it’s place installed a new proportioning valve from Maximum Motorsports. I followed their directions and this was a no-brainer.

After all is said and done, the hardest part of this swap is under the hood – replacing the booster, master cylinder, gutting the proportioning valve, and doing the 3-2 port conversion. But once it’s done, it’ll be a modification you’ll not regret as the braking becomes nothing short of amazing.