All 1983-88 Cougars (and all Thunderbirds save for the 1987-88 Turbo Coupe) had 10" front rotors from the factory. They're pretty dependable, cheap to replace, and generally wear very well. But for all of their positives, they were barely adequate enough to stop cars of our heft. We really should have had at least 11" front rotors, particularly on later (and heavier) Cougars. Fortunately you can upgrade to 4-lug 11" front brakes with very little effort. All you will need to change are the spindles, calipers, brake lines, rotors, wheel bearings, and the brake pads.
Words of caution here: only cars with 15" rims and bigger can use this conversion, since they need to clear the calipers. And you will need to get a bigger mini-spare tire from a Turbo Coupe or Mustang V8. If you've got a full size 15" spare, you're all set.
You will need the following parts from a 1987-88 Thunderbird Turbo Coupe or 1987-93 Mustang V8, except where noted:
You can use spindles from either the 1987-93 V8 Ford Mustang (GT or LX) or a 1987-88 Thunderbird Turbo Coupe; they're both the same parts. You can get them used at a salvage yard or online. The 1984-92 Lincoln Mark VII spindle will fit but requires modification of the ball joint attachment hole—avoid it. You will be able to reuse your struts, provided that you add spacers between the strut and spindle. This is because Mustang-spec 5.0 LX/GT struts are narrower where they meet the spindle, so using a Cougar/T-Bird strut will require spacers to properly work. Usually you can use a few washers to safely shim out the space (note: a lot of aftermarket struts actually come with spacers for just this purpose). We don't recommend simply tightening down your existing strut with an impact gun and no spacers—that can lead to the struts slipping, and cause major headaches the next time you need to remove the strut from the spindle. Please use spacers, or if you wish, you could just buy a pair of Mustang-spec 5.0 struts and install them.
You will need brand new calipers for this conversion; don't skimp and try to use junkyard pieces. They're best for using for a core when you get new ones. Remanufactured calipers are fairly inexpensive and cost-effective. Again you can use calipers from a 1987-88 Turbo Coupe or 1987-93 Mustang V8. The Mark VII is a much heavier car than a Mustang or TC, with the same size front brakes. As a result, the piston in the caliper for a Mark VII is bigger (73mm) vs. the Mustang/TC piston. This provides better stopping power, while still using the same caliper, dimensionally.
Whichever caliper style you choose you must be sure to get matching pads. You cannot use TC/Mustang pads with a Mark VII caliper, nor vice versa. Factory pads were semi-metallic and that's the least you should get (not organic!). Choose a good quality pad and you'll be set for a long time.
You will also need new caliper bolts to go along with your new calipers. They are a different type than your stock ones, and new bolts will have a hex head compared to your Torx-bit round head type, so there is no way to reuse your old ones. You will have to generously grease up the sliding portion before installation. Be sure to also get new banjo bolts and crush washers for the brake line attachment before installation.
The brake lines going to each caliper will need to be changed. If you want a stock part, Mustang lines work the best here, although the TC and Mark VII lines are probably the same thing. Compared to your old rubber lines, the new ones are about half rubber, half metal. This ensures better fluid pressure going to the caliper and also increases brake pedal feel. If you're really wanting a harder pedal feel for not much more money, then you can also use DOT-legal stainless steel brake lines meant for a Mustang V8 (Russell is the common brand). Don't forget to get new brake (a.k.a. "banjo") bolts and washers to attach the lines to the calipers.
You will also find that you'll need some adapters to get the new lines to attach to your car's permanent brake hard lines. This junction is in the strut tower area. Most of the time a 1/4"-to-3/16" adapter is needed, but you will need to double check this, as some years and models may have different sized brake lines. It's recommended that you use a steel adapter rather than a brass adapter, as brass has a tendency to leak. Adapters can be found at good parts stores including NAPA.
Only rotors from a Mustang V8 or Turbo Coupe will work for 4-lug wheels, since the Mark VII uses 5-lug. DO NOT use original Ford 11" rotors, no matter how good of shape you may happen to find them. The factory rotors were very thin and needed replaced quicker than normal. It's always a good idea to use new, quality brand rotors anyway. Prices range from roughly $45 US each on up, depending upon where you shop. The Turbo Coupe rotor should have the ABS exciter ring on the inside of the hub, and the Mustang will not. There may be a price difference between them; as you won't need the exciter ring it's likely cheaper to buy the rotor without one.
It's necessary to get new inside wheel bearings (the ones that go in the back side of each rotor), so it's a good idea to get new outside bearings as well. If you have just bought new outside bearings for the 10" rotors, you can reuse them on the 11" rotors if you'd like. But new bearings are cheap insurance. If you still have factory nylon bearings (yes, those existed!) then now is the time to upgrade to steel bearings. Be sure to get new seals also.
From the factory between 1983-88 there are two types of master cylinders:
Left: The traditional cast-iron type (1983-86) had 2 separate reservoirs for the fluid (front and rear), and two brake line ports (one for the front, one for the back). This type has a 7/8" bore.
Left: Beginning in 1987, most Ford vehicles switched to the aluminum type. Only one single plastic reservoir was needed, and brake pedal feel was increased due to its larger 1" bore. With this master cylinder there are three brake line ports (one for the front right, one for the front left, one for the rear).
Obviously you cannot easily interchange the two types (although we understand that there is a three-to-two line adapter kit available). However, either type should work just fine with the 11" brake upgrade.
Installation of the new components is pretty straightforward; the brake line junction might be a fun one for you if the lines are rusted but otherwise it's pretty easy. Once all is assembled, you'll need to refill your master cylinder with fluid and bleed the front brakes. When you're all done, don't forget that you'll need to get an alignment ASAP.
One area of concern that people have mentioned seems to be low pedal feel and they usually blame it on the stock master cylinder. If you've converted to 11" brakes and still believe the pedal feels low then it might just be that your stock master cylinder is just old and tired, and needs replaced. It seems like this brake upgrade, for some reason, will expose the flaws of the stock braking system rather easily.
If this is the case, you can definitely upgrade in the process. For the 1983-86 cast iron type, a 1984-86 Crown Victoria m/c works great, with its large 1 1/8" bore. For the aluminum 1987-88 m/c you can use a 1994-95 Mustang type without ABS brakes.
Also, try adjusting your rear brakes after you complete the front brake upgrade. A little adjusting of the drums might just help.
If the brakes still don't feel right, you can get a bigger brake booster (1994-95 Cobra is recommended), or stainless steel front brake lines (there are numerous aftermarket street-legal versions made for the Mustang that will work perfectly), or a combination of both. Whatever you do, DO NOT attempt to lengthen the pushrod going into the master cylinder! This will cause your brakes to totally lock up and you could possibly lose control of the vehicle. One of the above suggestions should solve your low pedal problem just fine.