Muscle Mustangs & Fast FordsHow To Drivetrain
Rearend Remake Part 2
With the help of JDM Engineering we completed the rear axle and suspension install on our Lightning-powered LX, and then we fixed our minor braking problem.
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Our little '86 LX, affectionately known as Frightning, is turning into a hot little street/strip Mustang. While our last track outing produced somewhat disappointing results (due to excessive tire spin), we were confident a solution would be easy to find. Our best elapsed time was 10.84 and we cracked 120 mph, but the torque-happy 5.4 Lightning mill put the coupe into severe tire spin on virtually every run and we couldn't realize the potential of the hopped-up Triton.
Since traction was the problem, we knew where to look to get hooked. We decided to rip out the tired (and mostly stock) rear suspension and rear axle housing, and install parts built for the rigors of drag racing, albeit ones that were right at home on the street, too.
In addition to the excess tire spin, we also had a small problem with the brakes. While our LX stopped pretty well (at least as well as it could with stock four-cylinder Mustang brakes), the conversion from power brakes to manual brakes left us with an ultra-stiff pedal that was difficult to push. No matter who drove the car, they couldn't get enough brake pressure and the car was almost impossible to hold in the burnout (we don't have a Line Loc yet). Forget about holding it on the line. Power braking it at all caused the car to creep forward.
Since this is Part 2, you may recall last month we delivered the Mustang to JDM Engineering in Freehold, New Jersey, and the surgery began. In Part 1, we yanked out the old rear and suspension components, most of which were rusted and/or rotted, and bolted in the Drive Train Specialists 8.8 using a Laurel Mountain drag launch kit (with airbag), UPR control arms and AFCO shocks. This month, we'll finish the job by making new brake lines to connect the Aerospace rear disc brakes, we'll set the pinion angle and solve the stiff pedal problem.
Completing the suspension install was easy. We had all the components in place from the previous issue. All that was left was to attach the line to the airbag and set the pinion angle. Our initial setting had the angle at 2 degrees positive. In this case the pinion was pointing up, when in fact, it should be sitting neutral or pointed slightly down. To achieve the proper angle, it is necessary to shorten the upper arms, which was easy considering we had UPR double adjustable arms in the car. JDM's Shaun Lacko shortened each arm a little at a time until the pinion was angled slightly downward. Ultimately, we ended up with -1 degree of pinion angle and -2 degrees of driveshaft angle for a total of -3 degrees.
Lacko then fabricated two brake lines to connect the rear calipers with the main feed line. We then filled the master cylinder with brake fluid and bled the system. A quick test showed the rear calipers were grabbing well, but the pedal was still hard as a rock. The pedal problem is a result of us using a master cylinder designed for power brakes, but without the power booster. To fix the problem it is necessary to change the pedal ratio, which essentially gives the driver more leverage when the brake pedal is pressed.
In order to accomplish this, we removed the brake pedal from the vehicle and relocated the pin the brake rod connects to. Raising the pin on the brake pedal shaft effectively increases the pedal ratio. When doing this you must be certain you don't upset the angle of the brake rod that connects the pedal to the master cylinder. If the angle is too severe it will cause side loading on the piston in the master cylinder and cause the seals to fail.
We also noticed the brake rod had been modified with a slight bend when the current master cylinder was installed. Fortunately, we were able to simply flip the rod over to maintain the proper angle once the pin was raised. If you find the rod is not straight when converting to manual brakes, it will be necessary to make a new mounting bracket and raise the master cylinder up to match the level of the new pin. As I mentioned, we lucked out and had proper alignment. We also had much improved brakes once all the parts were put back in the car.
Unfortunately, our busy travel schedule and a record amount of rainfall kept us from the track in time to give you real world results. But that doesn't mean we don't plan on getting to the strip real soon to flog the new suspension. Fret not, we have plenty of track testing ahead. To ensure we don't kill ourselves, we've procured a Stainless Steel Brakes rotor and pad upgrade for the front binders, as well a proportioning valve.
After that, we'll up the boost and shoot for the moon. Or at least the 9s.