Having finished the propeller shaft alignment, installation of the flex joint, rear transmission support bracket, transmission mount, transmission support plate and tightening up everything yesterday, I tackled the alignment of the rear axle. It was already close, since I did a quick and dirty measurement a few months ago when I installed it.
I don't have a "check gauge" because if I had made one of copper tubing, it probably would have been less accurate than how I finally did it. I'm really terrible at soldering.
My wife sews quite often and has all the makings of the perfect system, in my opinion. I used some of her needles, some thread and a magnetic business card from Rock Auto. I cut the card into some small circles, punched a hole in the centers with the needles and slotted the edge with scissors to capture the end of the thread after passing it through the hole. I made a slip knot after passing the other end through the needle so I could adjust the length of the thread easily. The photos show the details.
I taped two packing paper sheets together and taped them to my 4-post hoist "jack bridge". The magnetic card on one end of each thread was stuck to the end of the stud at the front mounting of the torque arm. The third one was stuck to the end of the rear axle suspension support arm pivot pin.
After adjusting the length of the threads to have the needles almost touch the paper packing sheets taped to the hoist bridge, I let the needles stabilize and stop swinging.
I then marked the three "needle" plumb bob end points on the sheet and used them as the basis for the "T" of the "check gauge" drawing on the sheets. Between the torque arm studs of my car, the measured distance was 875 mm instead of the 877 mm of the check gauge drawing. I decided that having the axle accurately centered on my car rather than to perfectly match a "supposed to be" check gauge design was the most important. I found the third "supposed to be" point (for the axle support pin end) by starting my "T's" vertical line at 459 mm from the driver's end of the "T" cross-bar line instead of 460 mm. That made the passenger side of the "T" cross-bar line 416 mm instead of 417 mm. I drew the vertical line of the "T" and it passed 5 mm from the axle support pin end plumb bob (needle) on the passenger side. Serendipitously, the 480 mm dimension of the check gauge "T" drawing turned out to be 482 mm on my car, so I ignored it.
So I got my wrenches and started working to eliminate that 5 mm error in the location of my axle. After about 15 minutes of working on the screw slot end of the cross strut, the plumb bob had not moved. So I said to myself, "Myself, what's 5 mm among friends? There must be something else not right." So I tightened the lock nuts and started gathering up my tools. Then, as I started to un-tape the paper sheets with the plumb bob marks, I noticed that the needles at the torque arm ends had moved 5 mm in the direction opposite of what I was trying to get the axle support pin to move.
As my mother would say, "Lo, and behold", I had not been screwing the axle toward the passenger side of the car. The plumb bob was hanging from the axle support pin which was fixed to the hoist and the hoist bridge and the paper "T" design by the tires sitting on the hoist ramps. It would never move, no matter how much I cranked the cross strut.
Instead of cranking the axle toward the passenger side of the car, I had been cranking the "car" toward the driver's side, so the torque arm ends, attached to the body, were moving to correct the error relative to the axle support pin end. The three plumb bobs, relative to their target positions were all exactly 5 mm away in the same direction, so my cranking fixed the problem. Even a blind squirrel finds an acorn occasionally.
If I had been using a check gauge, it would have been measuring relative positions of the three points. My plumb bob method works equally well, but one must remember that when you crank the cross strut, it's not the axle that moves, but the body end moves as you draw the body toward the axle support pin. I was blinded by perception. I was thinking of the axle relative to the car, when I should have been thinking of the car relative to the axle.
It's perfect now and I, once again, have learned a lot. On to the next project on the list.
Tom Kizer
