leafs should be located by the pins, so no real adjustments can be made there. If they were slightly crooked, the car wouldn't pull, it would dog-track slightly. Have you tried swapping tires side to side to see if it makes a change?

 

When the rear axle is not perpendicular to the frame of the car, it causes the car to roll down the road at an angle. This is commonly called "crabbing". (For some reason, almost every early Chevy Nova I see does this.) But no, it will not cause the car to pull in either direction.

 

What are your settings for caster, camber and toe-in? Do you drive "rural" roads? Do you have radial tires? Have you tried swapping tires side-to-side?

 

Toe in: 1/8" (in)
Camber: Left side: 0.5 degree (Negative) right side 0 degree
Caster: Left side Left (+) 1.2 degrees Right side: (+) 1.2 degrees

Radial Firestone Tires. I have tried switching front to rear and rear to front, keeping all tires on same side - makes little to no difference.

 

Try switching the fronts side-to-side.

 

Check your drums, both the fronts and rears, to see if one is dragging more than it should. I had a drum that seemed to be doing that on my trunk and it wound up being the self adjuster wire had broken on one.

 

The self adjusters from all drums are long gone. I set the brakes myself with just a bare minimum drag, but they're all the same.

 

When you put in the new springs did you change the short center bolts to tall ones?
all 65 and 66 mustangs need the tall center bolts all new springs come with short ones.
67 and up can use the short ones.
If you have the short ones your axle is most likely not correctly installed.

And you need more castor

 

Hmmm. Did the rear springs several years ago, and I'm not sure about those bolts. I seem to remember that I used whatever the springs came with, which is probably the short ones. I'll try adding more castor and see if that helps.

 

Seems to me that I read on this forum that radial alignment specs should be:

Hope this helps.

Gary

 

+ 5 on castor might be a challenge with stock parts and a bear to turn with manual steering.
+2.5-+3 should be possible with only minor fudging

 

Excessive road crown?

 

Interesting that you mention that because I see the outside tread of the front tires are worn, from alignment being previously out. The tires are from 2004, maybe a new set would solve the problem.

 

The 65-66 requires "tall" tie bolts to locate the axle. If the springs have been replaced, it is extremely likely that they have the "short" tie bolts. If so, the axle cannot be properly located on the pads. You can get the "tall" bolts from AMK or pretty much any Mustang dealer.

 

This should fix your problem....

 

Point of fact proven with 2 pencils, 2 sticks or whatever you have handy. The longer dimension on the right side, assuming it is the rear axle, turns the rear wheel outward on the front most side. That would give you a drift to the left, or driver's side. Now that we've established that dimension is not causing a right, or passenger side "drift", Do what Bart said, swap all 4 tires left to right, check you air pressure, and spin your wheels while you have it off the ground to make sure you don't have a caliper, or drum dragging. Get back to us.