7 speeds for Harley-Davidson

We are going to proceed with the assembly of a 7-speed kit on a Harley-Davidson, specifically on a Softail model with a Twin Cam engine.

Is it really necessary?
The first question I asked myself when I saw this kit was what reasons might lead someone to need an extra gear in these engines, which as of 2007 (2006 in Dyna models) are now equipped with the 6-speed Cruise Drive transmission as standard.

This original 6-speed transmission is an evolution of its 5-speed predecessor and uses helical gears (with helical teeth, rather than straight ones) to comply with increasingly stringent emissions (noise) regulations. It began with a design flaw in 2006 that was later corrected, and it has worked quite well to this day. This gearbox has a 1:1 final drive ratio, or "direct drive," which means that with the last gear engaged, the output shaft rotates one revolution for every revolution of the input shaft. To avoid this sounding too technical, we can compare it to "overdrive" type gearboxes, where the output rpm is lower than the input rpm, achieving a smoother shift but with less torque (remember the gear shifting on a bicycle: when you engage a smaller cog and pedal with fewer strokes, you get higher speed).
Although 6-speed transmissions perform very well, some owners find they lack greater agility when accelerating and shifting up, especially with boosted or larger engines (103ci, 110ci, 127ci, etc.), where a noticeable RPM bump is noticeable when shifting up. Added to this is a certain amount of excessive noise at certain speeds and loads, which, moreover, is a characteristic and does not pose any problem.

Let's go for the seventh
The kit we're going to install is manufactured by Baker Drivetrain, a world leader in innovation in gearboxes for American twin-cylinder engines.

This kit has a similar output ratio to the original 6-speed gearbox, i.e. 1:1, but by having one more gear all the gears are shorter, therefore gaining in acceleration, progressiveness and flexibility.
In addition to this advantage, Baker incorporates a series of improvements, such as a reinforced transmission door with wider bearings,

Diamond-cut gears with zero-backlash engagement, ARP bolts (used in Formula 1) and a shift drum that eliminates the old arm-and-spring detent system and installs a linear detent system with ball bearings, achieving a much smoother and more precise shift.

This, combined with the fact that they have applied a technique originating in the automotive industry, which consists of eliminating mass from the main shaft to avoid inertia (the HD shaft weighs quite a bit since it has the gears incorporated) almost completely eliminates the typical "clonk" when engaging gears (I will miss it).
The kit comes complete and directly and very easily replaces our 6-speed transmission, using only the transmission's crankcase.

Disassembly
Before starting, we must know that to correctly perform some of the procedures mentioned above, we need special tools for 6-speed gearboxes and, of course, the most important tool: our motorcycle's workshop manual.
Following the service manual, we disconnect the battery and drain the transmission and primary oils, after which we proceed to completely disassemble the primary transmission, blocking it with the special tool.

and we also disassemble the starter motor and the transmission pulley using a blocker.

We will continue using the specific tool to remove the clutch bearing race.

From here we can move to the right side of the motorcycle to remove the clutch mechanism cover and then the transmission “door” screws,

After this, we can completely remove the gears from the transmission. It's important to pull the door and not hit the shaft from the other side to remove the assembly, as this could damage it.

We take out the entire assembly and place it on a stable surface (it's heavy), and from here we can begin installing our new 7-speed kit.

Main Drive Gear
Now we just need to extract the main gear by removing the retaining circlip.

and then we use the special tool for this purpose, which will push the gear out of its location.

Please note that this operation will break the gear bearing, so it must be replaced with a new one.

Once removed, and still using the special tool, we reinstall the new bearing and the new main or direct gear, which will now transmit 7th speed.

Let's go for change!
Next, we prepare the main gearbox gear assembly for installation, removing the shipping ties and lightly lubricating the gears with gearbox oil. We then carefully insert the assembly into the transmission housing.

Once in place, we can proceed to tighten the ARP bolts that come in the kit to hold the transmission door in place. This operation will be performed following the order and torque recommended in the workshop manual.

We finished the assembly
Following the reverse order of disassembly, we install the top cover, the clutch mechanism cover, and the clutch bearing support.

and the propulsion pulley.

At this point, we continue with the complete assembly of the primary transmission, exhausts, etc. until the bike is ready to ride again.

Odometer adjustment
It's important to note that by modifying the gears, we've changed the gearbox's output ratio, so the speedometer won't work accurately. Baker has taken this into account and includes a device in the kit to easily reset the odometer to the new specifications.

Road test
It's time to check that the assembly was correct and evaluate the benefits of the new gearbox. After checking the oil levels and ensuring the gears engage properly with the engine off and the rear wheel elevated, we take the bike out onto the road.
Our test model is a Softal Screamin' Eagle with a 110ci (1800cc) engine, with a Thunderheader exhaust and a TTS control unit with a custom-made fuel injection map. In previous tests with the original 6-speed transmission it works quite well, although it lacks some aggressiveness, since the change is a little docile compared to the engine.
All this has changed after installing the DD7 kit. The engine now shifts up more powerfully, barely losing any revs, and the torque kick is progressive, leaving a tingling sensation in our stomachs when accelerating.
Another surprising change is that the typical "clunk" when shifting gears has been virtually eliminated; it's now just a "click," and the feel is absolutely precise and accurate. The noise coming from the gearbox at high speeds has also been significantly reduced.
The only drawback is that it's sometimes difficult to tell what gear we're in (not really necessary if you know your car), as you lose track. In our case, we installed a digital speedometer on the test model that constantly displays the gear, including 7th.

Conclusion
We therefore give this kit an excellent rating, which will delight those who like to "get into it" at traffic lights on sportbikes. It also provides a significant change in smoothness and performance, which translates into a big smile when you open the throttle.

Frank Burguera

#harleymechanics