DTS Harsh Ride

EDCAL

MEMBER
2002 CADILLAC DEVILLE DTS
V8
FWD
AUTOMATIC
107,000 MILES

I've had this car for 6 years. This car has experienced periodic vibration and harsh ride problems as long as I've owned it. I've had the wheels and all mounting surfaces, engine mounts and ball joints checked, replaced the steering rack, front struts, bearings, brakes and rotors and tried 4 different sets of tires (different manufacturers, road force balanced) - overall, vibration has decreased to reasonable levels, but on a smooth road the car often reacts strongly to the smallest bumps/road inconsistencies, and vibration in the steering wheel comes and goes (particularly at highway speeds). No DTCs are being set. I've consulted many experts including GM technicians and they are all stumped. The most common reason given is the tires - need the softest tires available, which is a joke since there are no such critters available (H and S ratings only). My question is, is the RSS responsible for this, or is it just the nature of the beast? Any suggestions to nail tis down?

5 Replies

RIVERMIKERAT

CERTIFIED MECHANIC

The electronic ride control could be setting it for a stiffer ride than you're used to. The DTS is sold as a sports/performance car, so a stiffer ride is to be expected. There should be a switch to set it between comfort and sport modes. The stiffer ride reduces body roll while cornering, giving you more control and steering feel while driving at speeds. The down-side is the slightly harsher ride.

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Wednesday, July 13th, 2011 AT 3:52 AM

EDCAL

MEMBER

Well, there appears to be no way to manually switch modes (ref. Service manual), and without a DTC being set, there is also no way to determine if there is a problem with the RSS selecting the correct mode for the surface/speed. It still seems to be too harsh on smooth surfaces, but performs great on rough roads. I will need a tech scanner to check if all functions are working properly. Thanks.

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Friday, July 15th, 2011 AT 12:39 AM

RIVERMIKERAT

CERTIFIED MECHANIC

This is true. Most parts stores like Advanced, Autozone, Pep Boys, and O'Reilly will allow you to borrow a tech scanner for little to no charge, usually no charge. Let us know if we can be of further assistance.
Vibration in the steering wheel can also be caused by minute changes in brake rotor thickness. If you have access to a thickness gauge, check the rotor thickness at many multiple locations around the rotor. I know you said you had the rotors replaced, but they may still have minute amounts of what we call runout causing the vibration.
Also, find a shop that will perform a high-speed wheel balance with the wheels on the car. This is the best way to balance the wheel as it is installed on the vehicle, making possible the greatest reduction in wheel/tire induced vibration.

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Friday, July 15th, 2011 AT 1:05 AM

EDCAL

MEMBER

The scanner needed is the certified GM version programmed for this specific vehicle's suspension and Bosch CVRSS, which is damn hard to find outside a GM shop (and usually only a Cadillac dealer at that, and they sure don't lend them!). As for a wheel shop that will do on-car balancing, no luck with that here. I checked thickness and runout on both front rotors - thickness on both had no measurable variation around the surfaces (less than 1 thousands of an inch variations). I cleaned all caliper bracket, rotor and wheel mounting surfaces, and installed the rotors on the car. The right one was right on (no measureable runout laterally or vertically). However, the left one showed a lateral runout variation at one point of 5 thous, with no vertical runout. When I mounted the wheels and checked the wheel runouts, I got the same results. According to GM, this variation is well within spec. I changed the pads, just to be sure - still no joy. Like I said before, this is puzzling - the only conclusion I can draw is that no company makes a perfectly round perfectly homogeneous tire for this car, and that the smallest torsional imperfection reacts badly with this RSS. But thanks anyway.

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Friday, July 15th, 2011 AT 2:38 AM

RIVERMIKERAT

CERTIFIED MECHANIC

Ok. The next option would be to have a tire shop with someone that knows his stuff balance the tires using a lug adapter plate, instead of the hub adapter that most use.
The road force balance you mentioned, if I recall my days in a tire shop correctly, ensures a perfectly round tire. Or is supposed to, at least.