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It's Time to Inspect Your Harmonic Damper
(But please don't call it a balancer)

by David Magnoli, TDR Contributor

The Installation Process

The first step in the installation is to remove the belt. If your belt-routing diagram sticker is missing, draw the path or take a picture so you can re-install it properly. With an automatic transmission the engine turns as you remove the damper bolts, so I removed the small inspection plate under the torque-converter and used a pair of Vise-Grips on the flex-plate, cushioned with a piece of leather, and let it stop against the transmission housing. With a manual transmission just leave it in gear and set the parking brake. After removing the four 15 mm bolts that secure the damper, it is an easy removal, as it is not pressed onto the crankshaft.

The dampers are hub-centric, having a close-fitting, center-bore that aligns with the machined snout on the end of the crankshaft flange. They are heavy though; be sure you get a good grip on it before removing that last bolt. After cleaning off the surface of the crank flange, and applying a little anti-seize compound around the center hole, I torqued the bolts to 92 ft-lbs as listed in the Service Manual. I used blue Loctite on these bolts, although there was none from the factory. I've read on the TDR forum that these bolts should not be reused as they are said to be torque-to-yield, but the Service Manual does not say anything about using new bolts. Obviously if they are damaged they should be replaced. Because I had torqued mine several times during the testing procedure, going back and forth between the different dampers, I replaced them with new bolts with the final installation. With the number of TDR forum posts about broken bolts, I would suggest that new bolts would be cheap insurance.

The Cummins part number is 4937228 is for years '07-current. The Cummins part number 3903857 is for years '94-'06.

First and Second Generation 12-valve truck ('92-'98) installation is fairly straightforward. There is plenty of clearance to unbolt the old damper and install the new one after removing the belt. With the larger diameter of the Fluidampr, you will have to relocate and rewire the magnetic tach pickup from the top of the crank to the side and then adjust the clearance gap to the pickup, which is best measured before removal. The needed parts and instructions are included with the damper.

You can read Scott Dalgleish's article about changing a 12-valve damper in Issue 18, page 23. Also, in TDR Issue 52, page 28, there is a situation describing the alternator not charging due to the crank sensor not being in alignment with the timing notch on the damper. When installing on a 12-valve this is something to watch out for.

Installation of both the ATI and the Fluidampr on my Second Generation 24-valve truck ('98.5-'02) did not require the removal of the fan or the radiator shroud, although it is recommended in the instructions. I was able to do the removal, although it is a bit tight, just by removing the belt and unbolting it. You can rotate the fan blades to a wide spacing to allow easier access.

Third Generation 5.9L trucks ('03-'07.5) and the 6.7L ('07.5-'09) have a slightly different installation due to the closer clearances. Again, the instructions state that the fan and shroud need to be removed, and although it does make it easier, I have seen it done on a '04 without doing so. (Editor's note: We also installed a Fluidampr on a Third Generation truck, a ë03 model, without removing the fan.) However, the serpentine belt must be routed between the damper and the water-pump pulley before the Fluidampr is installed because of closer clearances with its larger diameter. This also means that to change the belt you must loosen or remove it also. This is not an issue with the ATI, due to its smaller diameter.

Installation was easier since the Fluidampr is one piece, but that was only because I chose not to remove the fan and shroud. And because most of you will not be installing these four times in one day it will not really be an issue.

Road Test Results

After installing each of these dampers I took the truck out for a test-drive to see if I could tell any difference between them and the stock unit. Keep in mind that this is not by any means scientific, but rather a seat-of-the-pants evaluation of these products. I don't have the instruments to measure or record actual differences, only my impressions. I drove the truck all on the same day, changing dampers and going back over the same route for comparison. The truck was at operating temperature for each of the tests. I drove the truck with the various dampers as follows: stock, ATI, Fluidampr, and then stock again just to get a good feel for any differences. I drove for about an hour with each one installed and tried to cover many types of driving, from freeway to winding steep roads to stop and go traffic and was surprised to actually feel a significant difference.

Idle Quality

My truck does not have large injectors that cause a pronounced idle lope like some trucks do. The ECM (Engine Control Module) does not have to work very hard to maintain idle speed. But there is always that slight throb at idle when in gear that disappeared with the ATI and Fluidampr installed. The truck is dead-still at idle. This was confirmed when I re-installed the stock damper and could feel the throb return.

Manual-equipped trucks are said to have less gear clatter and to be smoother at idle with the installation of better dampers. I would think that a torque-converter, being a fluid-coupled device, would tend to be superior at absorbing vibrations at the rear of the engine than a clutch would, and would explain why manual transmission drivers would see a more dramatic idling improvement. Many claim reduced noise from the clutch. Also, with the installation of the damper on my friend Cliff Scott's truck, he noted that the truck was easier to shift into reverse.

Let's Drive It

At slow around-town speeds, there is nothing noticeably different about the aftermarket dampers, as the truck is not under much load under these conditions. Moving repeatedly from a stop did seem smoother with the two aftermarket models.

The real differences are noticed when driving under increased load. Under hard acceleration there is a reduction in the vibrations with the ATI and Fluidampr over stock. The engine just feels smoother. On a long incline with my truck in overdrive going 50mph, I'm only spinning around 1400rpm with my 3.55 gears and the engine is almost lugging. Accelerating hard to 2000rpm repeatedly resulted in much less of the shuddering I am used to when driving on this road. The vibrations in the steering wheel and pedal were greatly reduced under the increased engine loading.

Another area where I experienced a noticeable difference was at higher rpm. Accelerating in third from below 2000 to 3000 usually caused a dramatic increase in vibrations as the truck accelerated. This is also felt in the steering and the go-pedal. This has always been more noticeable with my Edge box turned up. With each of the aftermarket designs there was again a smoother overall feel under these higher power levels on the same stretch of road.

As far as any differences between the Fluidampr and the ATI, it was hard for me to determine. I would give a slight edge to the Fluidampr at idle and lower rpm, possibly due to the increased weight over the ATI. But, at speed and under load, I could not tell any real difference, as both were so much better than the stock damper. The other thing to consider is that although I could definitely feel an improvement in performance under several conditions, this is a part that does its job protecting the engine even if you can't feel it. A harmonic damper is not something that is designed or installed for the comfort of the driver; that is only a side benefit of it doing its job. In other words, it is designed to do a specific task. If you can feel the difference, great, but that is not the true test of its performance or protection. The fact is that the harmonic damper is protecting the engine, whether you can feel it working or not. Harmonic and torsional vibrations are very much an issue in our diesel engines, especially when power is increased, or when towing heavy; and, as mentioned before, the stock damper with its limited range of function only narrowly addresses this.

Conclusion

If your truck is stock, and your damper is in good condition, you probably do not need a better performing alternative although they are certainly a noticeable improvement. If however, you have substantially increased the power of your engine, I believe that you will benefit from the increased damping available from the aftermarket designs.

The problem that I see with a stock-design 5.9L damper, and the reason that I feel the aftermarket designs are so much better, is that it really does not absorb the vibration as much as just delay it, or throw it out of phase slightly. This, along with the fact that the bonded rubber ring only allows a limited range of damping, contributes to the stock damper doing merely part of the job assigned to it. Increased horsepower places more demands on our engines, and add to that the fact that the stock dampers do eventually wear out, and you have the need for an improved vibration-damping solution.

The ATI and the Fluidampr actually absorb the vibrations resulting in a smoother and more effective damping of the engine's resonance. Each of these designs allows the heavier internal inertia ring to float and move within the housing at a changeable amount dependent upon the varying inputs from the crankshaft. This allows them to self-tune to the variable inputs. They donít store any energy like the stock one does.

The ATI and Fluidampr are not only able to absorb more, but they also do it at a wider range of resonances, damping out the second, third, (and so on) order harmonics generated under increased engine loading. Being much heavier than stock means that there is more mass that the crank impulses have to work against and overcome, resulting in improved damping action. Another advantage is the fact that the pulley is part of the hub and not driven by a rubber ring, ensuring that the belt will always run true.

If your damper has failed and you are looking for a replacement, I would strongly consider the aftermarket type. If you are the kind of guy that just wants the best performance and you don't mind paying for it, you can replace your damper even if it does not show any signs of deterioration. Although that might seem wasteful, we tend to do exactly that with all the other parts of our trucks, often resulting in quite a few usable parts stacking up in our garages. Such is the diesel addiction. Although I was skeptical about the real-world advantages of these products, after my research and a direct comparison, I can clearly see the limitations of the stock units due to design and longevity issues and can very much feel the results of better damping. The two reviewed products have been around for a long time and have many miles of racing experience with high-rpm and rough usage. The quality, tolerances, and finish of both are excellent. They are not inexpensive, but their effectiveness is well-proven. They work and your engine will thank you.