I'm in the process of having spring perches welded on my narrowed Dana in my Dart. I had the rearend in the car with the new spring perches in place (not welded yet). I positioned the rearend equally from side to side and set the pinion angle then tightened up the u-bolts. My friend came over to weld the perches for me and tacked them in place before we pulled the rearend out to do the full weld. When we got it out of the car, to our surprise the perches were not positioned the same way on the rearend tube. The passenger side perch was tipped up noticeably when compared to the driver side. We are at a loss as to why this is other than perhaps it has something to do with the springs themselves.They are MP XHD springs and it looks like the perch bolts aren't positioned quite the same on the springs possibly causing the variance between the position of the two perches. Has anyone here ever encountered this situation?

All of the rear axles I’ve ever seen and checked have the perches mounted at same angle. I would agree that something is with the springs causing that. Possibly due to the diff spring rates of the xhd having extra leafs on pass side. Super stock springs would cause same if not more of that issue, I would think. Those actually pitch the entire car due to the add’l rate on pass side.

Also, and more importantly, are you sure that your ft. Torsion bar adjustment are correct? That could pitch the car and pit more weight on one side in rear. Ex., if you tighten dr side bar, weight will be transfered to pass rear and compresd that leaf. Are your bars adj. evenly right to left?

Yes, the torsion bars are set correctly. I'll have to check the number of leafs again tomorrow but I thought it was the same number on both sides.

Both Dana 60’s that I’ve had out of cars and checked come from factory with biased springs (6 leafs driver/5+2 halves pass) had the perches welded from factory parallel to eachother. And all 8-3/4” rears same thing. Perches welded from factory at equal angle.

Not sure what to think in your case, but definitely puzzling. In my opinion, I would weld them at same angle. Curious to know what the cause is when you find it.

The springs themselves will not set perfectly parallel. Cut the tacs on the housing and split the difference.
Doug

Totally agree!

The spring bolt on the driver side spring looks to be right at the bottom of the spring arch (hope that makes sense). The passenger side bolt looks to be a little more forward on the spring. We were thinking to just leave the driver side perch where it's at on the axle tube and reposition the passenger side to match the driver side. Does that sound like the right thing to do? Or would that push the passenger side of the axle a little more forward than the driver side?

It sounds like your saying one of the alignment register holes in the springs is ahead of the other one? They should be in the same location you'd think, or the axle may end up sitting out of alignment in the car. I would do some more measuring to see for sure.

I was just out in the garage and measured the spring bolt location on both springs. It's like an optical illusion. When looking at them from the side of the car, the passenger bolt looks like it is further forward on the spring than the driver bolt. However, upon measuring, I found they are the same length back from where the front hanger bolt goes through the spring. I think the problem then may be due to the curvature of the spring where the bolts come though the spring rather than the bolts fore and aft position of the bolt. Where the passenger side bolt is in the spring, the spring is already starting to arch up toward the rear hanger where the driver side there is a little more length behind the bolt before the spring starts to arch up to the rear hanger. I hope this makes sense.

Ok, so it's just the spring arch is not 100% the same.

Speaking of bolts make sure the register bolt heads in the springs are sized right for the hole in the spring perch holes. I bought ESPO springs many years ago the bolt heads and the holes in the springs were two different sizes so I had to change to a larger diameter bolt head and redrill the leaf spring holes out for the next size bigger bolts so it all fit together right. If those parts are not mated together right the axle can shift on the springs, which would be bad.

I would redo one of the perches so it matches the one you feel is most correct and go from there. If it's off a small amount once it's back together you can always add wedge shims to fine tune it as needed.

Just went out and measured the bolts and the holes in the perches. The bolts are 1/2" and the holes in the perches are 5/8".

That should be close enough. Mine were off a lot more than that so I had no choice but to fix them.

remember, tolerances in those days were +/- a mile, so anything within about 3/4" would be "spot on".

The good news is you can buy tapered shims to fit between the leaf spring and the perch to correct the pinion angle if it is wrong. They sit over the top of the spring center bolt. They can be bought as one or in pairs and range between 1 degree and 6 degrees. The shims can be added to increase the pinion angle, or reduce the pinion angle. The higher quality shims also lock into place with the U bolts (which becomes more important as the degree angles get higher the 3 degrees). Most 4x4 shops carry the tapered shims, or they can be ordered through 4x4 online resources.

Be aware that the shims sometimes require a taller pin to extend past them and fully engage the perch.
That can be done either with a taller pin end, or washers over/encircling the pin threads under the pin end.
As for the different saddle angles, I've never run into that on XHD or SS springs, that's baffling.
A body ft spring section is 20", spring eye to the pin.

I have ran into the same issue when installing SS springs on both the 69 Dart and 72 Duster...

It is a none issue if you are just putting new springs into a car where the perches on the rear are already correct...

If you were to lay the springs down one on top of the other you can clearly see the difference...

If I remember correctly when the LR perch was flat (tacked on at maybe 3 degrees down)...

The RH perch was indexed a couple to 3 more degrees...

Its almost like it is preloading the front half of the RR spring when you clamp the u bolts down tight...

On the 69 Dart the perches are slightly different and on the 72 Duster we tacked the LH perch and then mimicked the RH side to match...

Both cars leave hard and straight and have good traction so it may be a non issue for something that would be a daily driver or street car...

Not on any of Mopar H.D. springs, factory installed or over the counter sales

I do not have the perches fully welded on yet as I'm still trying to understand how to properly set the pinion angle. Been doing a lot of reading on the subject as well as watching videos and I must say it is very confusing with all of the different opinions I've read on how to do it. The method I have seen most often is simply to make the pinion parallel to the output shaft of the trans. and then drop the pinion down 2 degrees and lock it in. I've also read that it does not matter if the car is not sitting on a perfectly level surface, only that it is sitting on all four tires under it's own weight like it normally would. One thing I don't understand though is if for example, if the output shaft is pointed down say 3 degrees and you push the pinion up 3 degrees to make them parallel, then when you drop the pinion back down the suggested 2 degrees, this would leave the pinion up 1 degree higher than the output shaft. I thought the idea was that the pinion should be lower than the output shaft so when it is under load it would lift up to counter the 2 degree offset. What am I misunderstanding?

You need to have the car setting on the ground relatively flat with full race load weight measure the trans angle. The pinion angle should be parallel to the the trans angle under acceleration. How much angle does it take to do that. Super stock spring I’d start with 5 degrees. Examples: if trans is 2 down, pinion would be 3 down. If trans is level, pinion would be 5 down. If trans is up 2; pinion would be 7 down
Doug

Forgot to mention, another thing I read was you should have a full tank of gas (or comparable weight in the trunk) when measuring for pinion angle. This wasn't mentioned in all of the articles I read, just a couple. Is this true? Also, one article said to also have weight simulating a driver in the car as well as the full tank of gas.