Secondary Transmission Correa Maintenance

In this article we will talk about the Secondary transmission straps that equip Harley-Davidson models and some Japanese customs. These straps that transmit the rotation of the transmission output to the rear wheel remind us of other past times, where the transmission chains still did not exist, they are a simple element in appearance but they have integrated a lot of design technology to make them silent, reliable and With little maintenance.

A little history
The first secondary transmission belt in a Harley-Davidson was used precisely in the first 1903 model,

I left the famous wooden cabin in Milwaukee.

In those days it was a leather strap without teeth, quite rustic.
With the industrialization of production plants, the transmission chains arrived, until in 1980 HD surprised the motorcyclist sector by launching the Sturgis model, the only one in the world with 2 dentated transmission straps, both primary and secondary.

From this moment the dentated straps began to use more and more models, until in 1991 the Sportster model was the last to say goodbye to the classic chain.

Characteristics and advantages
Since its first appearance, transmission dental straps have always been seen with some skepticism, especially by sports motorcycles, since this type of secondary transmission seems more fragile than the steel chain. This is only in appearance, since due to its construction they are really strong and lasting.
The heart of these straps is made up of several ropes of Aramida, a material as hard as steel but flexible as fibers.

This material is the one that gives the hardness (elongation resistance) to the belt. To further improve its characteristics, Aramide is replacing carbon fibers and kevlar.
This core of strings is covered by the 2 sides with a layer of hardened polyurethane, material with which the teeth are also manufactured.
Finally, the part of the teeth is covered with another layer of a Teflon -based material for low friction.
As an example, I will tell you that you can lift an electra glide ultra with only 1 cord of Aramida! Current straps have about 10 cords ...

Maintenance and adjustments
One of the advantages of toothed belts of transmission is their low maintenance, since they do not require any lubrication, and are resistant to gasoline, oils and chemicals, and work well in extreme temperatures.
These straps do not have a mileage interval for substitution, they change when they deteriorate. The main causes of belt breakage are:
-A incorrect tension hall
-Desalineration
-Excessive particle drag

As you can check except the issue of particles (sand stones and others, depending on the environment where it circulates) everything has to do with the correct maintenance.
If the belt is very tense, it can break, if it is very loose, the teeth and pulleys will break when it is decelerated.
To correctly tense the strap we have to follow the instructions of the service manual of our year and model to the letter.

The belt must be checked and adjusted at room temperature (I have seen straps break them in the workshop with the heating at 20ºC and then rolling to the snowy roads).
The voltage check tool (HD 35381 or similar), because our finger does not have adequate precision.

The strap is checked by applying the pressure of the tool and the deflection or total movement of the belt is measured, if this is not adequate, the wheel axis is loosened and the belt is tense applying the same number of turns to the tensioners, or applying the same turn to the eccentric, according to the model.

We tighten the axis to the recommended torque (this step is very important to measure the voltage correctly) and apply the check tool to see if everything is correct.

It is important to check the alignment, we will do this with a Specific useful, to ensure that the distance between the rear wheel axle and the tilting axle is the same on both sides of the motorcycle, in this way the belt will work completely parallel with the pulleys.

For cleaning we will use neutral soap, and we will inspect the belt on both sides to verify that there is no wear or breakage. We will also check the pulley, replacing it if the wear is excessive.

To run!
For those who are making a long or adventure trip it is convenient for you to know that HD markets an emergency belt kit that can get us out of a hurry in a remote place.

So from now on we will “tighten” our transmission strap correctly, precisely so that it remains in good condition and lasts many years, in this way we will only have to concentrate on the really important: enjoy the road and the Good vibrations.

Frank Burguera

#mecanicaharley