Devils, Details and Weight Reduction

Ford Racing Aluminum Driveshaft

There are many things I could call this exercise. A party is not one of them.

I've spent three days crammed in the axle well of this 1989 Mustang with nothing to keep me company beyond a trouble light, a DeWalt drill on the very last of its legs and billion razor sharp, red hot slivers of metal with an affinity for my most sensitive of regions. My joints are raw from crawling around on the concrete. I'm half deaf from the shriek of the spot weld cutter and the boom of the cold chisel and hammer.

There are many things I could call this exercise. A party is not one of them. You see, after test-fitting the independent rear suspension from a 2004 Mustang Cobra into the old Fox Body I was left with the really challenging portion of the install: the details.

Technically, I could have simply plumbed some brake lines, said, "screw the emergency brake," dropped in a driveshaft and rolled, but I want this car to function in all the ways a road machine should, while still being able turn a decent lap on a road course. Combine that desire with a compulsion to scrape every ounce of unnecessary weight from the Mustang, and the result is me doing my best impression of a hammer-wielding Quasimodo, contorted into the void where the rear suspension should be.

Need to catch up on Project Ugly Horse? Take a look at the earlier posts here!

This all started logically enough. The old bump stops had to be removed to allow for proper suspension travel, so I sourced a cheap spot weld cutter and got to sending the old rubber bits to the scrap yard in the sky. Or, more precisely, to the scrap yard on Central Avenue. The parts came out with only the slightest bit of persuasion, which inevitably reintroduced me to a familiar old foe: unearned confidence.

Vestigial Brackets
Removing Brackets

Deleting the solid axle from the car had left me with a few bits of vestigial bracketry stuck to the floorboard with what appeared to be a haphazard smattering of spot welds. The backing plates for the old rear seat belts and the mounting points for the rear control arms sat there like a bunch of freeloaders. More importantly, they prevented me from cleanly routing new hard lines for the brake system. All told, the bits couldn't have weighed more than king size Snickers bar, but by glory, I wanted them gone.

Imagine sitting inside of a 50-gallon steel drum while an army of pipe-wielding toddlers wailed on the exterior.

After destroying every last tooth on my el cheapo spot weld cutter in the span of around six seconds, I broke down and purchased a quality tool from a local parts store. I also brought home a passel of extra cutting heads just in case, drew the shades and settled in for my new life as an axle well troll. I found that using a punch to set a center point in the weld itself did much to keep the cutter from walking, and all that remained was hours and hours of patient, diligent cutting. Wrapped as the control arm brackets were around the trunk pan of the car, some of the welds weren't accessible with the drill, which meant I was left to hammer the pieces off of the car with a cold chisel.

Imagine sitting inside of a 50-gallon steel drum while an army of pipe-wielding toddlers wailed on the exterior with all of the determination and persistence that particular age bracket is renowned for. Ear plugs can only do so much.

Still, I eventually succeeded without the neighbors setting fire to the house. I ground down what was left of the spot welds, cleaned up the 23 years of axle grease slung around the underside of the car and shot the whole thing with white industrial Rustoleum to keep the metal from going rusty. That just left me with sorting the brake lines. From the factory, the Mustang uses one hard line to supply the rear axle with hydraulic pressure. My new set up required two hard lines, so I picked up a brass T junction, mocked up my routing with some wire, picked up a few lengths of brake line and got to bending. Once I was satisfied with the way the lines looked and confident everything would fit in place without any interference, I mounted everything with a few plastic clips and self-tapping sheet metal screws. Another trip to Royal Brass and Hose served up a functional set of braided stainless brake hoses.

Finished Rear Brake Lines
Emergency Brake CablesBrake Line T-JunctionBraided Stainless Steel Brake Lines

Once done, I reinstalled the IRS cradle with only a modest amount of cursing and a more than a little help from a transmission jack. Let me just say right now that Harbor Freight makes an excellent example if you're low on cash. With the rear suspension resituated, I could turn my eye toward the emergency brake. Getting the more modern cables to cooperate with the ancient chassis was as simple as routing them up and away from the driveshaft. I used two of the old retainers to bolt the cables in place, and while the set up doesn't provide as much tension as the factory allowed, it will hold the car on a hill. Still, I'll probably leave the machine in gear as a safety precaution until I can come up with something better.

That left just one very crucial part of the recipe: the driveshaft. As you may recollect, I had been using an old salvage piece from a GT to pump power from the T5 transmission to the old solid axle, but the independent rear suspension meant the rear flange would no longer mate to the differential. Never one to pass up an excuse to upgrade, I turned my lust toward an aluminum Ford Racing driveshaft. Shut up, Freud. You don't know me.

Ford Mustang Driveshaft Comparison

Not only did the new piece weigh in at 15 pounds, but it also came with brand-new universal joints throughout. Now, I ordered a driveshaft that would fit Mustang GT models built between 1979 and 1995. The part offered the correct spline count for the transmission and was the correct length, but came with the foreboding warning that it would not under any circumstance work with a Cobra of any ilk. Under the presumption that, like Freud, the internet doesn't know me, I clicked buy and waited patiently for the UPS truck to show up at my door.

Once it did, I quickly found out why Cobra models were a no go. The companion flange on the IRS differential is simply too large to bolt to the flange on the driveshaft. One call to the Mustang salvage shop and $20 later, I had a GT flange that would party. In the photos below, the GT flange is on the left, the stock LX flange is in the center and the Cobra flange is on the right.

Installing the Driveshaft
Mustang Companion FlangesReverse Companion Flanges

Use too much or too little torque and you'll soon be picking bits of ring and pinon gear from your fancy 8.8 rear end.

All that was left was the tightening, as they say. Or so I thought. As it turns out, the companion flange is held on with the pinion nut. Smart mechanics mark where the nut lies in relation to the pinion itself because there is one very important crush sleeve in there. Stick things back together with too much or too little torque and you'll soon be picking bits of ring and pinon gear from your fancy 8.8 rear end. Of course, I only remembered this the second the air gun stopped spinning the pinion nut off the differential, leaving me with no way to know where everything was situated from the factory. Sweet.

Some internet sleuthing served up the correct preload for the pinion, though there's still some possibility that the whole set up is borked. I may be forced to retrace my steps to make sure everything is sitting pretty before putting any real miles on the machine.

Complete Driveline

With the driveline complete from stem to stern, I had planned on focusing my efforts on getting the suspension settled. But projects like this have a knack for taking your plans, balling them up and setting them on fire with boundless glee – in the best way possible. Somehow, Ford Racing had gotten wind of what I was cooking up with Ugly Horse, and they wanted to know if I needed help finding something to put in the engine bay.

Why, yes. Yes I did.

Need to catch up on Project Ugly Horse? Take a look at the earlier posts here!