ZW7 is the premium smooth ride option, which means you're truck was originally equipped with the Nivomat rear shocks. They may have been replaced at some point with standard shocks. Some say the rear springs on the ZW7 trucks were softer since the shock incorporated some kind of automatic (non-air) load leveling feature, but I'm not certain on the softer spring/non-softer spring deal.
The Premium Smooth Ride (zw7) is a rear Nivomat & front regular shocks. The Nivomat rear are load bearing self leveling shocks & fully self contained (& stupid expensive). The stock coil springs are lesser tension & softer because they share the weight/work with the Nivomat shocks.
Parts I just used today converting from OEM Premium Smoothride system (will work as conversion on all OEM suspension systems for @ least years 2001-2006, some systems will require a resistor so dashboard warning light doesn't stay on)
Bilstein 5100 series Rear Shock Part #24-187237
Bilstein 5100 series Front Shock Part #24-186643
Bilstein Coil Springs Part # 199021 (also known as #15711646)
(I used 5100 series because they give room for lift which I plan on doing later but you can use the 4600 series. Spoke to Bilstein & they told me they were same shock, the 5100s just allow for 1" lift in front & 2.5" lift in rear & were different colors).
Today I replaced my 2003 Chevy Tahoe's 4 OEM shocks & springs. I put on the new shocks first but not the springs so I could see how it went without putting in the stiffer springs. The rear end sat lower, felt like it was loaded down or had load on the hitch. The right & left rear side moved around a lot more independently of each other & bounced much easier & longer.
I then went home & put the stiffer springs in. The truck rides like new. I was afraid I would lose some of the smoothness but hadn't. The Tahoe is more responsive, rides smooth & the new set up leveled out the truck perfectly (although I prefer the raked stance).
Stores like Autozone, napa etc wanted over $125 for each shock but I got them for less than half that by going to products site & finding local distributor & parts were ordered & available for pick up in 24 hours.
I (average joe driveway mechanic) did the whole conversion. It took about 2 hours in my driveway with limited tools & no spring compressor needed.
I researched this for over month on forums, sites, at performance shops, product manufacturers etc. I firmly believe this is the easiest way to convert from the overrated stock OEM system to one that rides very closely to OEM, fully functional & are a superior quality product. Once the new rear springs are installed you can put on any shocks that fit the z71 package for your year. Bilsteins best bang for your buck @ $444 for 4 shocks & 2 springs.
Hope this helps anyone considering converting your Chevy SUV or truck.
