7 speeds for Harley-Davidson

We will proceed to assembly a 7 -speed kit in In a Harley-Davidson, Specifically in a softer model with Twin Cam engine.

Is it really necessary?
The first question I asked myself when I saw this kit are the reasons that can lead someone to need one more march in these engines, than from 2007 (2006 in the DYNA models) they already equip the 6 -speed Cruise Drive Transmission standard.

This original 6 -speed transmission is an evolution of its predecessor of 5, and uses helical gears (with propeller -shaped teeth, instead of straight) to comply with the increasingly strict emission regulations (noise) and that had a start with a design defect in 2006 that was subsequently remedied, working quite well to date. This box has a “ratio” of final output of 1: 1 or “Direct drive”, which means that with the last speed the output shaft rotates 1 return for each round of the entrance axis. So that this does not sound too technical we can compare it with the “Overdrive” type boxes, where the output revolutions are lower than those of entrance, getting a softer but with less torque march (remember the change of marches of a bike, when you engage a smaller pinion and with less pedaling you get higher speed).
Although 6 -speed transmissions fulfill their work very well, the truth is that some owners miss a greater “agility” when it comes to accelerating and going from marching, especially the enhanced or large cubic motors (103ci, 110ci, 127ci ...), where a “pothole” of RPM is excessively appreciated while changing a superior march. To these we must add some excess of loudness to certain speeds and loads, which on the other hand are a characteristic and do not imply any problem.

A for the seventh
The kit that we are going to install is manufactured by Baker Drivetrain, world leaders in innovation in exchange boxes for American bicilindrical.

This kit has an output ratio similar to that of the original 6 -speed box, that is, 1: 1, but by having 1 gear plus all the marches are shorter, therefore gaining acceleration, progressivity and flexibility.
In addition to this advantage Baker incorporates a series of improvements, such as a reinforced transmission door and with wider bearings,

Gens with diamond and grocery cut without slack, ARP screws (used in formula 1) and a change drum that eliminates the old arrest system by arm and spring and installs a linear detention system with ball bearing, achieving a much softer and more precise change.

This, together with which they have applied a technique that comes from the automotive consisting of eliminating mass from the main axis to avoid inertia (the HD axis weighs quite a lot since it carries the incorporated gears) almost completely eliminates the typical “clonk” when the marches are engulfed (I will miss it).
The kit is complete and replaced directly and in a very simple way our 6 -speed transmission, taking advantage of only the crankcase.

Disassembly
Before starting we must know that to correctly perform some of the aforementioned procedures we need special toilet for 6 -speed boxes and of course, the most important tool, the workshop manual of our motorcycle.
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 engine and transmission pulley using a blocker.

We will continue using the specific tool to extract the clutch bearing track.

From here we can already pass to the right side of the motorcycle to extract the clutch mechanism lid and then the “door” of the transmission, transmission,

After which we can completely extract the gears from change. It is important to pull the door and not hit the axis from the other side to extract the set, since we could damage it.

We take out the whole set and support it on a stable surface (it is heavy), and from here we can start with the installation of our new 7 -speed kit.

Main Drive Gear
Now we only need to extract the main gear for which we remove the cirp from fastening

And then we use the special tool for such a task, which will push the gear outside its location.

Keep in mind that this operation will break the gear bearing, so you have to replace it with a new one.

Once outside and always using the special tool we install the new bearing and the new main or direct gear, which will now transmit the 7th speed.

For the change!
Next we prepare to prepare the main gear set of the gearbox for installation, removing the flanges that come for transport and lubricating the gears with gearbox oil. Then we introduce the set in the transmission crankcase with great care.

Once in its place we can proceed to tighten the beautiful ARP screws that come in the kit to hold the transmission door. This operation will be carried out following the order and tightening pair recommended in the workshop manual.

We finish the assembly
Following the reverse order to disassembly we are installing the upper lid, the clutch mechanism cover, the clutch bearing support

and propulsion pulley.

At this point we continue with the complete assembly of primary transmission, escapes, etc. Until we have the motorcycle ready to roll again.

Adjusting of the accountking
It is important to know that having modified the gears we have changed the output ratio of the gearbox, so the speedometer will not work exactly. Baker people have thought about this and includes a device to easily readjust the accounting to the new specifications.

Road test
The time has come to verify that the assembly has been correct and evaluate the advantages of the new gearbox. After checking the oil levels and the gears engage well with the standing engine and the rear wheel we remove the motorcycle on the road.
Our test model is a SCREAMIN SOFTAL 'EAGLE with 110CI engine (1800CM3), with TUNCHERHERHEADER and switching TTS escape with custom -made injection map and in the previous tests with the original 6 -speed transmission it works quite well, although some aggressiveness is missed, since the change is a bit docile compared to the engine.
All this has changed after the installation of the DD7 kit, now the engine rises with more force marches, without losing just revolutions, and the "kick" is progressive, leaving us a tingling in the stomach when accelerating.
Another change that has surprised us is that the typical "clonk" has practically eliminated when the marches are engulfed, now it does not go from "click", and the touch is absolutely precise and exact. The noise from the gearbox at high speed has also decreased a lot.
The only "but" is that sometimes it is difficult to know what march we circulate (it is really not necessary to know if you know your machine), since you lose your account. In our case we install the test model a digital speedometer that indicates at all times the march, including the 7th.

Conclusion
We are thus giving an excellent note to this kit that will delight those who like to “chop” in traffic lights with sports motorcycles and also provide a change in smoothness and very important benefits, which translates into a big smile when you open gas.

Frank Burguera

#mecanicaharley