Whichever name you want to know it by, this out-of-sight, little known, sometimes misunderstood, integral part of the drive train on our boats can ruin your day and cruise if not maintained. For purposes of this article, we will settle on the name Drive Damper, since it best describes its function and location.
Where is the Drive Damper?
Located in the bell housing between the engine and transmission, the medium pizza-pan sized drive damper is usually bolted to the flywheel of the engine and spline connected to the transmission. Its purpose is to absorb or dampen the torsional impact and noise of the power stroke from the engine. Without the drive damper, the continual pounding of the engine’s explosive power strokes could cause transmission chattering and possible damage to the transmission.
What is it and how does it work?
Composed of two separate discs that are connected by flexible springs, or Teflon or polyurethane pucks, the flexible connection between the two discs cushions the engine’s torque impact. Both diesel and gasoline engines need drive damper plates to protect the transmission and eliminate gear chatter, especially at low RPM. Drive damper plates come in a number of varying sizes and torsional rigidity. The correct drive damper is sized to the horsepower and torque of the engine. Some plates use laterally mounted springs for shock absorbing, others use several puck-shaped flexible donuts between the two discs.
They don’t last forever!
Because of their location between the engine and transmission, it is impractical to inspect drive damper plates. Inspecting them requires nearly as much time and effort as replacing them. It is sometimes possible to visually check them with a borescope or through vent holes in the bell housing; however, this cursory view may not reveal their entire condition. The normal service life of a drive damper plate is 2,500 to 3,500 hours. Usually the shock absorbing connection between the two plates is the point of failure.
What happens when they fail?
At best, when a drive damper plate fails, it effectively acts as if the transmission is in neutral; with no forward or reverse capability. At worst, broken metal pieces of the plate scrape, score, and damage other bell housing or drive train parts. No matter what, you won’t be going anywhere with that engine and transmission.
What is involved in replacing them?
The drive damper plate part varies in price from $200 to $450. However, the process for replacing it is quite involved and labor adds to the cost. The transmission needs to be removed from the engine. To provide the needed space, the prop shaft must be pulled back, which is usually done when hauled out. Occasionally, removing the shaft coupling from the transmission provides enough space to remove the transmission. In many instances, the aft end of the engine must be supported before the transmission is removed.
Unless you are supplying your own labor for the job, the cost of the part becomes a very small part of the cost for this repair and replacement project. However, given the undesirable consequences of a failure while cruising, it is a small price to pay to replace these parts before their service life expires.