 April 2008: Isolated Drive System - Part 2
Band-Aid For A Symptom?
I believe kinetic energy pulses, or refraction, roll backward from the rear wheel pulley and through the powertrain. They reenter the transmission from the back, causing the backlash clatter in fifth-gear. The mainshaft and countershaft fifth gears absorb the power pulses creating the noise via backlash clatter. Backlash occurs within the mating spur or straight-cut gears because the gear teeth are not in constant contact. There are spaces between the gear teeth. Sixth, fourth, third, and second gears are helical cut, so the gear teeth are in constant contact with each other. Thus, backlash is not an issue in helical-cut gears. If there were no spur-cut gears in the Cruise Drive, this fifth-gear clatter would not exist. Of course, the refracted energy pulses might manifest themselves in other ways. Or they might not manifest at all, just roll back and forth like exhaust pulses. The spur-cut, first-gear set does not make any discernable refractive backlash noise because the fifth gears have already absorbed the returning pulses.
The Echo Chamber
The offending noise emanates evenly in all directions from the transmission, but the primary covers act as an echo chamber, resulting in the belief by some that the noises originate here. Switching from Syn 3 fluid to thick transmission hypoid gear oil will lessen, but not eliminate, the clatter. Why is this not a burning issue with the 2006 Dyna, where the six-speed Cruise Drive was first used? I think a number of factors easily explain this.
The Dyna is lighter, its riders more prone to higher rpm riding. We already know that riding at higher rpm in fifth gear will lessen and/or cause this gear clatter to cease. Dyna riders do not smell the roses as much as the touring bike owners do. Furthermore, the Dyna rear pulley is two-nubs bigger (68) than the 2007 Twin Cam (66), resulting in a higher secondary ratio of 2.13:1 for the 2006 Dyna versus 2.06:1 for the 2007 Twin Cams. The Dyna has a final drive gear ratio of 2.88:1 versus 2.79:1, and an overall gear ratio of 2.96 versus 2.70 for the Touring Models. Therefore, the refraction whip is pulsing with a different wave configuration. Also, the Dyna and Softail primary system is a different shape and length from that on the Touring Models. The internal webbed support structure and dampening system is also of a dissimilar style. Result: The echo chamber effect is muted.
I think the final answer of why the problem occurs in only 2007 models is actually a combination of factors, with each one alone incapable of causing the power-pulse refraction noise. First, the secondary, final, and overall gear ratios are unique to 2007 and 2008 Twin Cams. However, the 2008 touring models have the IDS system installed right from the factory while the 2007 models have the traditional rigid-mounted rear pulley sprocket. The sprocket shaft roller bearing has a part in transmitting power pulses, too. Ordinarily, the engine’s compensating sprocket can cope with these power pulses in combination with the sprocket shaft roller bearing, especially after realizing and checking the crucial torque specification procedures of the compensator nut. In contrast, the tapered Timken sprocket shaft bearings allowed up to and beyond 400 ft.-lbs. torque, or however much the backyard mechanic could muster with no ill consequences.
An Aggravating Culprit?
However, the kicker that brings this noise problem all together is the super-sized primary gear ratios compared to the conservative ratios in predecessor Twin Cams. We move from a compensator engine sprocket of the antecedent 25-tooth up to a radical 34-tooth. This overwhelms the compensating sprockets’ capacity to absorb power pulses as effectively as before. Higher gearing always encourages the possibility of spark knock, especially when overcoming the effects of the massive sprocket going up the rpm range. The pulses roll down the powertrain only to return back via the rigid-mounted, energy-transferring, rear pulley sprocket particularly at lower rpm levels. The returning harmonic pulses find the absorption point of least resistance, which, in this case, is the spur-cut fifth gears.
The IDS cure is to rubber-mount the rear pulley sprocket to absorb traveling pulses and prevent their transference back, or at least disrupt the wave pattern of the pulses. Harley-Davidson, in order to preserve traditional design, goes to inordinate lengths to mask symptoms as opposed to curing some problems. We now have compensator sprockets at the front and rear of the powertrain to curb the fifth-gear clatter. Therefore, the spur-cut gears are not the origin of fifth-gear clatter, but the end result of harmonic pulses traveling unhindered back and forth along the powertrain, much like exhaust pulses do in the exhaust system. Time will tell how reliable the rear rubber-mounted pulley is.
V-Rods spearheaded the IDS system. However, the high-rpm V-Rod’s torque curve is different from the Twin Cam curve. The last time H-D attempted a rubber-mounted compensator was long ago, with the disastrous Shovelhead FXS Sturgis. Rubber technology has improved drastically since then, plus the IDS rubbers are larger and doubled in number. So, if you’re experiencing the clatter on your 2007 FLHT series Twin Cam, then I feel confident this may be your fix (“enhancement”?) for dampening the mechanical noise! An all helical-gear transmission, like that provided by S&S Cycle, would eliminate a noise problem without requiring a dampening solution. Ditto with the BAKER Drivetrain F6F helical-gear fix for the Cruise Drive.
IDS Installation
Whenever installing any kit, always use the Harley-Davidson workshop manual in conjunction with the instructions sheet supplied with the parts. In this case, use the 2007 Touring Manual (#99483-07), along with “Instructions: Isolated Drive System -- J04467, Rev. 2007-06-28.” We can see that the release date for the IDS is June 28, 2007. As with any mechanical work where injury may occur with accidental start-ups or battery-powered rotation of parts, it is crucial to disconnect the battery ground and the maxi-fuse before doing any work. Also, remove any rings and hanging jewelry, such as necklaces and wrist chains. Loose metal objects can short across powered electrical parts. Rings can leave perfect scars around fingers if they cause an electrical short.
The IDS installation is straightforward. Just follow the removal and installation of the rear wheel instructions in the manual. The instruction sheet that comes with the kit is informative and clear. There are two instructions of note. The first is the bearing (#40670-06) installation into the new final drive sprocket pulley (#40265-08). Use H-D’s rear wheel compensator sprocket bearing remover/installer (#H-D-48921). Also, use this tool for the removal of worn bearings when servicing and replacing with a new bearing. The second instruction of note ensures the new pulley sprocket threaded holes are deep enough for the new 7/16”-14 hex screw bolts and captive washers (#3814) that hold the compensator bowl (#40560-05) to the rear wheel. A 7/16”-14 x 1-1/2” go/no-go gauge (also called a gauge screw) is supplied with the complete kit (#40287-07). The 7/16”-14 x 1-1/2” designator means the hole is 7/16” in diameter with 14 threads per inch, which is a standard-sized national coarse (NC) thread. The bolt hole threads to a depth of 1-1/2” deep. The stock wheel bolt hole threading may not be as deep as indicated by the go/no-go gauge Screw. If not, thread them to 1-1/2” with a 7/16”-14 tap.
Use hot soapy water and a nylon brush to wash away any old threadlock material from the sprocket pulley wheel mounting holes. Do not use a wire brush of any type. After lubricating them with a half-and-half mix of water and isopropyl alcohol, install the six rubber isolators into the compensator bowl (#40278-08) according to the instruction sheet. Do not use oil or any other petroleum-based product for this purpose, as it may cause the rubbers to deteriorate. Align the compensator bowl mounting holes with those in the rear wheel. The bowl obviously must face out for the pulley sprocket lugs to interact with the installed rubbers. Now install the bolts and captive locking washers in the standard crisscross pattern. Tighten them in an alternately pattern (back and forth) until you attain a torque of 65 ft.-lbs. (88Nm).
Next, install the inner thick spacer (#11846) against the inner compensator bowl bore. Re-lubricate the rubbers with a 50/50 mix of water and isopropyl alcohol where they will contact the sprocket pulley lugs. Install the sprocket pulley, ensuring the lugs seat fully. When installing the wheel, use the outer thinner spacer (#11844) provided in the kit. Tighten the axle nut to the manual-specified torque to seat the parts. Loosen and retighten, ensuring the compensator bowl lip does not contact the inner sprocket face at any point in its circumference. You can then reconnect the negative ground cable and the maxi-fuse. Go for a test ride with the hope that the previously noisy gear clatter will be dampened/eliminated as a result of the IDS absorbing the engine-generated power pulses.
ConclusionThe IDS currently retails for around $375. This Harley-Davidson riding pleasure enhancement should offer a successful Band-Aid for the annoying fifth-gear noise, to both the rider and the EPA. |
Why 
Linear Mode
