Some 2015-2020 Transit vehicles equipped with rear wheel drive (RWD), single rear wheel (SRW) and a U-joint at the transmission flange and rear driveshaft may experience a boom/hum/moan noise or vibration from the rear while driving. This noise or vibration is most prevalent at highway speeds (112-121 km/h 70-75 mph for 4.10 axle ratio, 121-128 km/h75-80 mph for 3.73 axle ratio, and 136-145 km/h 85-90 mph for 3.31 axle ratio) and may also be present to a lesser degree at roughly half of those speeds. This may be due to a 2nd order driveline frequency transmitted through the rear drive shaft, rear axle and into the body through the leaf springs. To correct the condition, follow the Service Procedure to install a driveshaft torsional damper.
