Differential/Rear suspension build up and installation

Started off with a bare housing from a 91GT. This differential is 59.25" wide from wheel mounting surface to wheel mounting surface. That is two inches wider than a stock '65-'66. The axle tubes are 2-7/8" in diameter, and comes stock with 4 lug axles, 28 spline track-lok, and drum brakes. Ford has a 5 lug axle/drum package for about $250.00. For the average street car pushing 400HP or less this is a great way to go.

I Used a cutoff wheel and a grinder to remove the control arm/shock brackets and grind down the tubes smooth. Took about 30 minutes. Care needs to be taken not to grind into the axle tube itself.

With the front of the car up on ramps, and the rear of the car supported on jack stands I removed the stock rear end as a complete unit.

I cut out the stock muffler to make way for the Panhard Bar, pressed out the stock spring bushings and cleaned and painted the springs. The Caltracs come with aluminum spring bushings, and an inner steel sleeve. I used the heavy polyurathane bushing grease on the steel sleeves.

I installed a Prothane Heavy Duty shackle kit with poly bushings. When installing the bushings it is much easier to install it as an assembly. Otherwise trying to get the bolt in later is impossible. Use lots of the supplied grease.

I set the bare housing up on the jack and rolled it under the car. set the perches on the springs and noticed the spring bolt was much smaller than the centering hole. I had a piece of 3/8" I.D. pipe and made a spacer for each spring bolt to keep the axle properly centered. Hooked up the front spring eyes and set the perches in place, then lowered the axle housing into the spring perches. I put the U-bolts over the axle tubes and used the Caltrac spring plates to secure the whole thing just snug.

Next I raised the assembly high enough with the floor jack to assemble the shackles. With everything in place it was time to level the car, and get the springs compressed so that the axle was at the stock ride height. I added about 300 lbs into the trunk, then jacked the rearend up by the differential. I used an incidence meter on the rocker panels to level the car, and set stands under the rear jack points.

I then lowered the rear end down until it was at the proper ride height and used blocks under the spring plates.
This sets the car at the normal ride height, and level so that you can measure and set pinion angle. Seeing as I still have the 6 cylinder, I went ahead and measured the engine/transmission drive line angle (turned out to be 4 degrees), but decided to use the stock 3 degrees pinion angle (as engineered by Ford). When the V8 goes in, it will go down and back reducing the engine/transmission angle back to 3 degrees. For now I'm running 1 degree shim plates to match the transmission angle and pinion angle.
Next step is to center the rear end housing in the car. This is very easy to do with the new aluminum front bushing and HD Polyurethane shackle kit, as the springs have no side to side deflection. I loosened up the Ubolts and slid the rear end side to side until the measurement between the edge of the spring and the axle flange was the same on both sides.
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So that sets the rear end side to side, but there is still one more very important check. Go as far forward as you can and find a point center of the car. For me this was easy. I had installed a Rack and Pinion, and still had the center of the cradle marked. From here I ran my tape measure to the lower front axle flange bolt hole on each side. The idea is that the distance from each side of the axle to the center near the front of the car should be exactly the same. I was fortunate enough that it was. This tells me two things. One, no major damage has happened that bent the unibody. And two, the car was initially built straight out of the factory...What luck!
I scribed a line at each spring perch where it sat on the axle tube.
Using the same incidence meter I set the pinion angle. And double checked to insure I did not push the axle housing off center.

Here is a good article on pinion angle

Now with the pinion angle set and the rear end centered, I tack welded the perches in place. Then removed the axle housing, and completed welding the perches on.

At this point, I put the rear end back under the car and checked all the same measurements as above. Nothing moved or warped so life is good. I primered and painted the rear end housing and started on assembling the differential.

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