Originally Posted by steven1955

2007 V8 Limited, non air suspension, non XReas, and 105,000-ish miles on the OEM springs. Bilstein 5100 shocks with the front shock snap ring set for 0.85 inch lift. 5100s have only about 15,000 miles on them, so don't want to replace them.

I know my answer is somewhere in the forum, but after hours of reading, reading, and reading some more I decided to ask for advice.

When empty except two people with groceries the 4R is nicely leveled. With four people and hiking gear the rear is only slightly low. But when we really load up the rear sags too much.

At first I thought that an air lift bags would be the easiest fix, but my GF drives the 4R more than I do, and I worry that the bags might leak down below the minimum inflation pressure and get damaged because I wouldn't always be able to check them out.

Questions and thoughts:

1a. Do the OEM springs go soft or are they prone to failing at 100,000+ miles?

1b. Maybe replacing the springs makes the most sense. While we don't need to lift Dobinson, and maybe others, make progressive rear springs with a mild lift,

2. Assuming there is no reliability based reason to replace the OEM springs, can you reasonably make air lift bags leak free enough to not be an issue. Like only having to check the every couple of weeks?

3. I know there are on board compressor based air lift control systems, but I think I'd rather spend those hundreds of dollars on a Bilstein 5100 compatible 1.5 to 2.5 inch lift. I would prefer a slightly firmer ride and maybe a little more roll resistance.

4. Are there any progressive rear springs other than the Dobinsons?

Thanks for any guidance you 4rth gen experts may offer.