Date: 201901
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Landing
ATC / advisory: Tower ZZZ
Aircraft component: Landing Gear
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: Other landing roll
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Just after touchdown of all three landing gear and aircraft in reverse thrust operation; the aircraft shook dramatically left and right. The aircraft was also pulling hard to the right side of runway; required full left rudder input from flying pilot. I (Captain/non-flying pilot) reached over and turned off the Auto-Brake System; which cured the pulling to the right problem. I then took control of the aircraft from the First Officer with the ship still shaking left to right; this diminished with slowing rollout speed and eventually stopped at taxi speed. [We were] unable to determine any abnormal indications from cockpit instruments; rudder control and tiller steering all operated normally. With the aircraft still rolling unhampered; I informed Tower Controller we would clear runway southbound. Also informed Tower of our situation and the possibilities that we may have blown or shed a tire or tires on the runway; suggesting an inspection should be performed.Tower closed runway immediately; instructed aircraft behind us to go-around; and dispatched an Airport Operations Vehicle to inspect our aircraft. This inspection yielded normal tires all around; nothing abnormal except fluid around left main gear assembly. Subsequent checks in cockpit found good brake and hydraulic systems; pressure and quantity. Rolled aircraft ahead to test each brake and steering; informed Ground Control we would taxi aircraft on into ramp; [and we] parked aircraft. Had also informed Operations of this event and possible need of tow assistance as well as a mechanical inspection post flight; to be passed to Maintenance Control at Operations. Post flight inspection found the left main landing gear shimmy damper assembly had failed and broken free at the lower torsion support; and was completely missing from aircraft. At my request those parts were found on the runway and most of the bigger parts were returned to my aircraft after the runway surface was swept and cleared.Identification: After landing touchdown (all three gear) just after reverse thrust application. This was a 90 degree crosswind (15 to 18 knots no gust) however the First Officer did a normal crosswind landing; I.e. NOT a hard or side-load landing or a one main first hard or side load type event. Landing was a normal crosswind landing. We were first aware just after touch down when the aircraft shook left to right; very dramatically at higher speeds; and pulled to the right side of runway.Cause: Failure of the shimmy damper and or the torsion support links holding the shimmy damper unit on the left main landing gear; with extreme shimmy conditions it would appear this unit broke completely free from the gear assembly (parts found on the runway).Suggestions: Inspections of all of the fleet's shimmy damper assemblies.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew reported experiencing heavy vibrations and directional control issues after a landing that was later traced to a failed main gear shimmy damper.