8 3/4 perch to flange difference?

[Glenwood]

I'm squaring up the 70 axle housing and noticed the passenger side is 1/4" shorter from perch to housing flange. Is that normal and to do with the adjuster?
The perches are 44" apart and seat fine on my 64s springs but I'm wondering if the perches are not positioned properly. They look original and not relocated.
The 64 8-3/4 axle housing is equally spaced from the perches to the flanges.

 

[Cranky]

Mom had a horrible tolerance on stuff like this including the body. My 71 Cuda had a pretty big difference from the left to the right when I welded up a set of 8" rallye wheels for it. The rear end was ok but each wheel had to have a different offset in order to get 275-60's in the stock wheel houses.....and the car had never been wrecked......

 

[GITEX]

My 65 is tighter on the left by a 1/4"

 

[Glenwood]

Just to make it more confusing, I put a straight edge on the housing flange and measured to the outside of the frame above. The driver's side sticks out 1/2" more than the passenger side. For fun, i inserted the axles and measured from the edge of the axle flange center to the frame which is still 1/2" difference and nearly 1" difference to the outer wheelhouse lip. The perch to axle shaft flanges remains 1/4" difference or more.

 

[Yatzee]

I'm squaring up the 70 axle housing and noticed the passenger side is 1/4" shorter from perch to housing flange. Is that normal and to do with the adjuster?
The perches are 44" apart and seat fine on my 64s springs but I'm wondering if the perches are not positioned properly. They look original and not relocated.
The 64 8-3/4 axle housing is equally spaced from the perches to the flanges.

Indeed it does and I believe that this difference was allowed for lining up the rear diff with the offset the motor had. What's a 1/4 inch here or there in the big picture of things. You will also notice that when you raise the axle to the springs, the springs (or at least one)cant inwards a bit and I believe this inward camber of the springs was engineered into the suspension because the rear spring shackles are slightly narrower on center than the front torque boxes mounting points. This will naturally tighten spring movement weather they are compressed or extended.

 

[Cranky]

If you ever look up under an E body on a lift, you can notice by eye that the rear hangers are wider than the front hangers. The leaf springs are splayed wider at the rear and is noticeable. Can't remember the actual measurement but it was noticeable and was done to help in handling....sort of a poor mans rear steer but it works. As for the factory building in the offset to help stay in line with the engine is something I've never read or heard about before but having the rear moved over for it isn't going to make much difference if any with how it would affect driveshaft angles if it's not perfectly inline with the trans. In fact it would most likely be a good thing for the U-joints and vibration if the rear was not perfectly aligned with the trans but if one is looking for the least amount of HP loss, align things very close to straight but that's not the greatest approach for U-joint longevity. Drag strip use is another issue I've gone around and around with this subject with a lot of people and well, I know what works for me. If I'm building a rear end for myself on a street car, I'm going to align it with wheel clearance in mind along with engine offset too but with more than 40" of drive shaft length, I'm not too worried about being perfectly in line with the center line of the engine/trans combo. If the rear is already in the car and I'm doing up some wheels, then I'll just test fit them before welding the centers in.