A crawler vehicle undercarriage which comprises a first cylindrical track frame pivotally mounted to a vehicle frame and a second cylindrical track frame telescopically received within the first track frame. An idler is pivotally and rotatably mounted through a cushion pad to a forward end of the second track frame while a drive sprocket is mounted to a drive shaft. A track chain encompasses the idler and the drive sprocket and is in driven engagement with the drive sprocket. A recoil spring is interposed between the first and second track frames for urging the idler away from the sprocket to maintain track tension. First and second crank members are pivotally mounted to the first track frame with a common pivot axis. A bogie is pivotally mounted to the respective crank members and a pair of track rollers are pivotally mounted to each bogie, the track rollers engaging the track chain.