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Todd Dills

Got fatigue? Your crankshaft damper may be the problem

| July 10, 2014

An often overlooked source of fatigue — not to mention equipment damage — that’s relatively easily mitigated with routine preventive maintenance is a stressed crankshaft damper, reports Brian LeBarron of Springville, N.Y.-based viscous damper manufacturer Vibratech TVD. LeBarron, with colleagues, took the time recently to spell out the issues in a report for customers he shared with me.

Viscous damper design incorporates a free rotating inertia ring surrounded by fluid inside a sealed housing. A Vibratech TVD viscous damper uses specialized silicone that is clear and gel-like in viscosity.

Viscous damper design incorporates a free
rotating inertia ring surrounded by fluid inside a sealed housing. A Vibratech TVD viscous damper uses specialized silicone that is clear and gel-like in viscosity. The damper is located at the front of your engine, mounted to the external face of the crankshaft. Its function is to reduce engine vibration created naturally from the force of combustion.

We’ve had reports on the damper periodically here, notably from both Pittsburgh Power’s Bruce Mallinson and Kevin Rutherford, when the latter was still authoring our monthly Dollars and Sense feature in the magazine. Mallinson and Rutherford both advise replacing the damper after your rig has passed 500,000 miles. Rutherford noted associated mechanical problems that can result if you don’t “run the range of broken alternator brackets, broken air-conditioning brackets, clutch and driveline problems and even loose or faulty electrical connections.”

Replacement could cost anywhere from $700-$1,000, noted Rutherford.

While both Rutherford and LeBarron note there isn’t a really easy way to inspect a damper for problems, LeBarron’s piece offered some helpful illustrations of some of the problems, noting that the damper’s control of engine vibrations means prolonged crankshaft life, reduced wear on accessory components, improved valve timing and an overall contribution to better fuel economy.

A visual inspection does not fully indicate a damper's operating abilities. This damper came from an engine that had been rebuilt but the damper was not replaced. The deteriorated condition of this damper was a major factor in the failure of the crankshaft (see the below image).

LeBarron concurs with Rutherford and Mallinson that a visual inspection does not fully indicate a damper’s operating abilities. This damper (pictured, above) contributed to a crankshaft failure. Pictured here with the cover removed to reveal the dark, thickened silicone that indicates it is beyond its effective service life, the damper came from an engine that had been rebuilt but the damper was not replaced. LeBarron notes that organizations training managers and techs may “brush over the topic” of the damper, “so it’s not in [techs’] processes to replace the damper, though if they would it could help lower warranty expense on rebuilds and generate greater customer satisfaction.” The deteriorated condition of this damper was a major factor in the failure of the crankshaft.


The general recommendation found in service manuals is to routinely visually inspect a viscous damper for signs of dents or leaks. If those are found, replace the damper regardless.

Here is shown the broken snout of the crankshaft from the above-mentioned failure. The general recommendation found in service manuals is to routinely visually inspect a viscous damper for signs of dents or leaks. If those are found, replace the damper regardless — the 500,000-mile (or 15,000-hour) interval, or whatever your engine’s service manual states, is also a good rule of thumb, LeBarron notes.


silicone dried up

After that long interval, the silicone inside the damper slowly undergoes a hardening process, and its ability to reduce vibration is diminished. Eventually, this uncontrolled vibration becomes evident in the cab, where it leads to greater fatigue. Uncontrolled vibration also creates all sorts of maintenance issues, as stated above. These can also include throwing and slapping of belts, broken accessory brackets and accessory drive gear wear, broken and loosening bolts, loosening bolts, excessive main bearing wear, loss of fuel economy, loss of torque and horsepower and broken camshafts. One way to save money on labor is to include damper replacement during in-frame rebuilds.  

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  • norman ott

    How true this is, I have seen this first hand, we had a truck that keep throwing belts all of the sudden without warning all belts come off. Can’t count how much we spent on belts. We changed damper 4 years ago haven’t had a problem since. I know KR is a snake oil salesman but is right on this one.

  • localnet

    I bought my current truck a few months back, an International ProStar money pit with the Cummins ISX 600 CM871 motor. I have been going through the mechanics of the truck as money and time allows… I replaced the damper at 700,000 miles at my local Cummins dealer. I went with the OEM damper after doing research on PP’s damper setup, which more than a few guys had issues with as far as fitment and clearances.

    When I had the damper replaced, upon picking up the truck, the difference in what I heard and felt was very noticeable. The Cummins motor now runs like a Singer Sewing machine… And I would attribute the old damper to the demise of my AC Compressor, Alternator and tensioner pulley. The vibration the old damper was putting off was not noticed until it was replaced, if you understand what I mean, and it was pretty bad.

    Also, the old damper looked OK, nothing really there to tell you if it was good or bad visually… But it was bad, so don’t think a visual inspection will work in diagnosing a bad damper.

    If you have over 500,000 miles on your ride, spend the money and get the damper replaced. I figure that I have added many more miles to that Cummins motor by taking the time to have this work done. The damper replacement cost me $1050, $580 for the damper and the rest in labor.

    Next up, a new clutch… Which I also attribute to that damper, the clutch/tranny has smoothed out with the new damper, but is still not right. strives to maintain an open forum for reader opinions. Click here to read our comment policy.