I am having some Firestone Coil Rite Air Helper springs installed on the rear of my 4wd SUV. Is it necessary to have an Alignment done when this is completed? I have gotten a few quotes with some who say it is necessary and others who don't. I appreciate any 3rd party expert opinions. Thanks!!
Anything you do to the vehicle that alters the suspension geometry - shocks, springs, tie rods, etc. should be followed with an alignment.
Typically, new springs alter the camber - how much the tire leans in towards the vehicle - which requires an alignment unless you want to be buying tires soon.
Now, with the "helper" springs that go inside of the existing spring, the question comes down to whether the vehicle sits higher or lower, or at the same height, as before. If it's unchanged, you might get away without an alignment. However, stiffening the spring may change the height - stiffer springs won't compress as much, so the truck will sit higher, which alters camber.
Given that alignments are cheap, especially compared to the price of the spring kit. I would just pay the $75ish and get it done. Many places will give a discount on the alignment if you're having other work done at the same time.