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1969 Ford Mustang Boss 302 Trans-Am Brake Swap - MMF Tech
Upgrading Your Classic Colt With Vintage Trans-Am Hi-Po parts
The braking system on the 1960s Mustang is certainly adequate as long as the car is equipped with power discs on the front. We looked to improve braking performance further, and make it bulletproof even on a track day. However, on a car like an original Hi-Po '66 fastback, a '68 Shelby GT350, or a '69 Boss 302, you may want to maintain some sort of vintage appearance rather than bolt up a set of monster billet aluminum calipers and rotors. This is of even greater concern when these modifications require cutting and welding to such a rare Pony.
Our test mule for this article is out of the Christiana Muscle Cars (New Castle, Delaware) stable-a real '69 Boss 302 Mustang. The Boss is similar to the rest of the 1960s Mustangs with 11-inch power disc brakes, and 10x2-inch drums in the rear. The only real difference is that the Boss came with 15-inch wheels, which are required for this brake swap.
Having driven this '69 Boss 302 at a bunch of open track events and drag races, we knew that the braking distance was not only related to the brake system performance, but the overall grip of the tires on the car. So before we did any brake distance testing, we called up our guys at BFGoodrich and ordered up a new set of their P245/60R15 BFG Radial T/As.
The big brake kit we are going after was created in the late 1968, early 1969 seasons of the Trans-Am road racing championship. The front calipers and rotors are off of a big Ford like a Thunderbird or LTD. These binders feature massive four-piston calipers originally made by Kelsey-Hayes. The race teams fabricated a custom bracket to adapt the calipers to a Mustang spindle. You can almost see Bud Moore doing a brake job on his grandma's Ford LTD and thinking, "We should use those brakes on the Trans-Am Mustang."
The front brake setup is really a conglomeration of parts. The foundation is a '70 Mustang drum brake spindle, which has a larger stub which uses a larger bearing than a disc brake spindle. Also, the hub is a disc brake piece off of any disc brake Mustang. The calipers and rotors are right off the shelf in the parts store, along with the brake pads, which are from a '66 Ford Thunderbird. The tricky part is the caliper bracket, which is a custom-made piece. Lastly, the rotor is a larger 12-inch diameter-one full inch bigger than stock. This complete front brake kit, which includes everything you need from spindles to steel-braided brake hoses, can be purchased from Christiana Muscle Cars for $2,450.
The installation of the front brake kit requires you to get a little dirty and involves a couple of steps. First up is the dirty job-packing the bearings and installing the grease seals on the hub. The tricky part involves the '70 drum brake spindle, which is slightly different than our '69 Boss spindle and will require a frontend alignment when all is said and done. We took this as an opportunity to go for an aggressive street/open track alignment. We added a bit of caster and went with a 1/2 degree of negative camber, which helps with stability when turning into corners. This was definitely an improvement.
Just like the front setup, the rear brakes were sourced from a larger Ford car, such as a Torino. In the later 1960s, the Trans-Am teams switched to a disc brake setup in the back, but that required welding on the rearend. This is taboo in our theme of keeping a classic Mustang intact with no cutting, welding, or adding of modern-looking parts. So, we called Master Power Brakes for its big drum brake kit (PN DR 1504K), which retails for $495. This kit comes with huge 11x2-inch rear drums with cooling fins. This is 1 inch larger in diameter over the stock setup in all '60s Mustangs. The kit increases the size of the brake shoes and the drums. The larger drums do add weight, but the added surface area helps to disperse more heat, and the fins help keep the drum cool from warping under excessive braking that you would experience after a day at the track. This will decrease brake fade and give the driver more confidence.
The kit is preassembled with the backing plates, shoes, springs, and wheel cylinders. It almost bolts itself onto the car...well almost. The installation is pretty straightforward. The toughest part is getting the parking brake cables off the old backing plates and hooked onto the new setup.
Since we were replacing the stock brake setup on the entire car, we went ahead and contacted Classic Tube and installed a complete stainless steel brake line kit, including its trick new steel-braided Stop Flex brake hoses-our one concession to the modern era. This is also the perfect time to change the brake fluid. Most people never think about changing their brake fluid, but the fluid traps moisture and will quickly cause the brake fluid to boil and fail under extreme situations. If you plan on taking your car to a track day, many times the track will require you to have changed your brake fluid within the past year. Christiana Muscle Cars recommends using regular DOT 3 brake fluid, as it believes that synthetic brake fluid does not last as long in the system before it turns color and begins to damage the internal brake parts.
Now is the time to call your buddy with a strong right leg and bleed these massive brakes. It takes more than a few pumps just to get fluid out of the front calipers because they hold a ton of fluid. Once all four corners are bled and all the lines and bolts are double checked, cautiously take the car for a testdrive. Take your time and be careful with newly installed brakes. A simple bolt that is not tight or a line that is a bit loose can cause you to lose your brakes and get into an accident-not good. Be sure to give them a few good pumps once you start the engine and before you roll out of the driveway.
The stock baseline test was done at Atco Raceway in New Jersey on a sunny 81-degree day. As we all know, classic Mustangs do not have antilock brakes. This becomes increasingly apparent when measuring the stopping results. Once the tires lock up, it can be like hitting a patch of ice. The car seems to take off and just blow right by the desired stopping point. So, car control and brake pedal management is increasingly important even with the new brake setup. We averaged the best two runs on the stock setup and came away with a 60-0 mph stopping distance of 139 feet.
After the brake upgrade, we had the frontend aligned and took a couple of easy testdrives before heading to New Jersey Motorsports Park in Millville, New Jersey, for an open track weekend. The final brake test came about a month later and the air temperature was only 70 degrees, with cloudy skies. This is not a big swing in conditions, but the pavement temperature was considerably cooler, which often reduces grip.
With the Trans-Am upgrade, the difference in braking was immediately apparent. Stopping distance was dramatically reduced, especially from 120 mph going down the front straight on the Thunderbolt track. However, this article is about results, so while we were at NJMP, track manager and Mustang vintage racing guru, Joe Volpe gave us some time on the front stretch of the Lightning course to do our final stopping test.
With the upgraded Trans-Am-era braking components bolted on, our 60-0 stopping distance average checked in at 130 feet. While 9 feet may not seem like much, it's more than enough room for you to avoid an accident, or brake later into every turn on the road course. Plus, with the larger components, brake fade will be lessened.
Once we finished our brake distance testing with the new brake setup, we installed a set of super trick race-type brake pads from Porterfield for the rest of our open track weekend at NJMP. Once these racing-type pads warm up a bit, they really slow the car down well at racing speeds. Running the Boss around the road course is much more manageable now with reduced brake fade, more overall stability, and increased driver confidence. It's a small price to pay for all the brake dust on the front wheels!