W126 300SEL pulls to the left before and after alignment
 

The car is fairly new to me and I'm still working out the bugs. New wheels and tires, new shocks, and now I had it aligned. Here is the spec sheet.
Here are paraphrased comments from the alignment tech:

"The springs are sagging especially the ones in the back therefore you have to compensate the settings a little to adjust for the shorter springs"
"the rear camber cannot be adjusted without shims but they don't use them anymore"

The car tracks straight if I hold the wheel straight but drifts left if I let go of the steering wheel. It drifts more if I apply the brakes. I have tried this on roads where the road crowns to the left, middle and to the right.

Any thoughts?

https://farm1.staticflickr.com/966/3...fee67b7c_b.jpg300SEL Alignment by ttownthomas, on Flickr

If the suspension bushings, ball joints, tierod ends, etc are worn out, there's no alignment in the world that's going to make it drive straight.

Sagging springs in the rear on the LWB 126 seems to be common. I just replaced the ones in the SDL and the difference is nothing short of amazing.

Swap front tires to back and see if it clears up.

The suspension rubber is surprisingly solid for the age of the car. It was a san fran area car. I had a master tech friend of mine that has some mercedes experience look at the suspension and we both felt the ball joints, bushings and tie rods were in excellent shape.

Good idea.

I rotated the front ties left to right. The tires are Michelins with less than 2000 miles on them. Plus the wheels are brand new. At this point I need a shop recommendation.

How do I figure out if the rear springs indeed need to be replaced? Can they be measured?

Full tank of gas and empty trunk and rear seat. Go park on a very level surface (parking lot or some such place) and back up a good 50 feet or so and look at the car. Does it look like the rear is sagging as if you have a sack of concrete in the trunk? If so, stick a fork in the springs.

assuming my pulling issue is a brake caliper hanging up or somthing. There is also an on-center vagueness at interstate speeds. I assume this thing tracked straight as an arrow when new.

Do the sagging rear springs affect the car in a way that makes it wander vs hold the line? Or perhaps the alignment compensation made from the sagging rear introduced a bit of something.

If I do replace the springs are there some other "while I'm in there" parts that should be done. The shocks are new.

If you do have a brake caliper dragging, it should be relatively easy to find. Go run a highway speeds for 10-15 mins, pull over and go feel the front wheel hubs. If you have one that's markedly hotter than the other, you know that wheel has the brake dragging.

The steering box is recirculating ball, so there will always be some slight vagueness, they are not as tight as rack and pinion. How much slop do you have in the steering wheel? How far can you turn it back and forth without making the car wander? If you have a helper, you can have them turn the wheel slowly back and forth while you watch the tie rod ends and pitman arm. See if there is movement before the wheels start moving, if so you have worn tie rod ends and/or center link. They'll definitely contribute to a wander/weave/pull.

In my experience, the wimpy rear springs won't really contribute to a wander or weave unless there's a side wind. Prior to the spring replacement, my car was a pain to drive at 70+ on the interstate on a windy day. The springs have calmed it down considerably.

If you're going to do the springs, replace the spring pads (go OEM for this part, it's cheap) and the differential mount at a minimum. They will all be removed to change the springs, so it's an ideal time to swap them out. Consider draining and refilling the diff oil while you're under there.

I already got my spring "points" from the FSM. Should I buy the spring from MB too?

You can if you want, the springs aren't very expensive, nor are the rubber pads. Lesjofors has a good reputation and that's who I used for mine. The host of this forum has them on their website.

My part number only comes in a bilstein spring from the host. 116 324 11 04

Has anyone had success with a Billstein W126 rear spring set?

I'd suspect Bilstein is decent quality. They make decent shocks. So long as the spring rate and ride height is the same as OEM, that's all that really matters.