What options are their for adjusting the suspension height on a century class?

Adjusting the valve is super easy.
Find the levelling valve under the rig, look for a rod that goes from the axle to the valve which is normally on the front drive axle.
Loosen the nuts that secure the valve in place, and then move it up or down to adjust the ride height.
Another option would be to add bump stops to the suspension, to stop it hitting the body work. They can be polyurethane to make it softer if it does hit them.
On freightliners, I have found there to be quite a margin of error when it comes to drive line angles, it takes a lot before they start to give a harmonic vibration issue.
I work on a lot of Range Rovers, which have air ride from the factory, as well as build rock crawling Jeeps etc. So have had plenty of experience with drive line angles, bump stops, and so on. Principals for them are the exact same as for a big rig.
A cheap angle finder from a hardware store will help you fine tune the drive line angles too, as already said. I use a digital Craftsman one, but they sell them at Lowest etc for a few dollars too.

Martin

 

The simplest way would be to have the height set correctly by someone that knows what they are doing, then make extentions for the bump stops to make them low enough so the tires will not rub when you are in the positions that they do now. You should still have enough axle travel in normal driving.

EDIT: I guess we were both posting this at the same time.

 

Ok, This is how you do "it". You have to know "where" the specification is measured. On my Mack it's from the bottom of the spring hangar to the bottom of the frame and measured on the front drive axle. Mack actually has a piece of gauge shaped like a tee......but you can't buy it. Mack let me trace it on paper and I took it back to the shop, transferred it to aluminum plate and cut it out.

Truck has to be on level ground. Unhook the rod from the top at the valve handle, move the handle to inflate / deflate to get the spec distance required at the spec location. Valve handle has be on center so no air is flowing either way before you measure. Measure from the bolt hole center of the valve to the bolt center of the bottom of the rod, that's the length the rod needs to be.

Rod too long? Cut rod in middle and take out extra, re-attach using 2 screw clamps and a piece of mini hose and make rod proper length or get new rod. Bolt it up, your done.