Lots of excellent information on this site. What suspension system/components are there on a 98 Deville. I recently purchased one and although the ride is good it does thump on city streets going over bumps. Trying to figure out how to diagnose the problem.

My 98 Deville came with (non-electric) Air Leveling Shocks in the rear, and (non-electric) Struts in Front. But Cadillac also put the expensive Electric shocks/Struts on the same model. If you call your Cadillac Dealership (parts department) and give them your VIN (vehicle identification number), they will be able to tell you what type of suspension your car has. I have the same problem with the "Thump" sound coming from the rear suspension when going over bumps. I have changed the Stabilizer Bushings/Links and the Shocks on the rear of my Caddy but the Thump is still there although the sound is less noticeable now. I will be changing the front Struts, Stabilizer Bushing and Links on the front suspension next week, and hopefully that will further eliminate the thumping sounds. I'll make another post here, once I've completed the front suspension and let you know if it improves the "Dreaded" thump that we seem to be plagued with..

I owned a 96 Deville Concours with the CVRSS system, exact same problem. Seems to be more predominant on this setup than the standard RSS. What happens is the air levelers over-inflate themselves when there is no heavy load in the rear. This in turn results in an unforgiving, hard shock that when run over bumps just leaps off the road. To fix my problem I replaced the suspension with a used RSS form the salvage yard. Result: Smooth ride, no thumps.

check the lower rear hub bushing. my 98 has a bad one which causes the thump. I'm trying to locate a replacement bushing instead of replacing the whole hub for $200. Know anything about this?

dm