Some owners of a 2016-2018 Cadillac XTS may comment that a vibration is felt in the seat under heavy acceleration around 20 mph. The condition may be caused by a second-order vibration (driveline shudder) from the cardan joint.
1. Raise the vehicle on a lift.
2. Remove one of the front differential mount bolts.
3. Loosen the opposite side front differential mount bolt.
4. Position the specified flat washer over the differential mount washer (see below for washer P/N)..
5. Loosely install the bolt enough to support the differential.
6. Remove the other front differential bolt and position a flat washer over the differential mount washer.
7. Install the bolt.
8. Tighten both bolts to the specification listed in the service manual.
The 14 x 42.5 x 3.61mm flat washers are available as P/N 11562546.