Today’s modern transmissions are the most complicated component of the vehicle. Hundreds of parts are assembled with precision to give you precise shifting and performance. One of the components that live inside of the transmission is the transmission band or sometimes called a transmission brake band. Let’s take a closer look at what a brake band does and the common symptoms of loose transmission bands.
How does a transmission band work
Just like a manual transmission, an automatic transmission transfers the power of the engine through a series of gears to gain different speeds and torque outputs. While a manual transmission does this by simply meshing gears together to transfer power (think of your bicycle gears). The automatic transmission does this with a series of planetary gear sets.
A planetary gearset is a combination of gears that can provide different gear ratios and even reverse by holding and driving various combinations of gears. The band is constructed of a metal backing with a clutch material (known as friction material) that resembles the material that you would find on a manual vehicle’s clutch.
The transmission band is a holding device. It holds a component of the transmission to prevent it from spinning and holds a component.
The transmission brake band is wrapped around a component known as a drum. With a machined outside surface it gives the transmission band a place to hold when needed. This drum generally does double duty in the crowded space inside of the transmission and inside will hold a multiple disc clutch that will generally drive a different component.
When the transmission control module decides it needs to shift gears and the band needs to be engaged, hydraulic pressure is passed through the valve body by a combination of electronic and mechanical shift control valves. This fluid causes a piston to extend and clamp the band tightly against the drum stopping and holding it securely.
What causes a loose transmission band
The band is designed with a friction material wear surface, over time through normal use the friction material will start to wear down. The transmission fluid aids in preventing this but eventually the wear gets so bad that symptoms begin to appear.
The other cause that can have symptoms very similar to a loose transmission band is a hydraulic seal that has failed. The transmission brake band relies on hydraulic pressure to engage the band. If a seal has failed it can leak out hydraulic pressure as it tries to engage the band piston. This causes the band to slip resulting in similar symptoms as a loose transmission band.
Symptoms of loose transmission bands
The most common symptom of loose transmission bands is slipping into gear. When the transmission control module requests a shift the transmission band takes a longer time before it can hold the clutch drum. This causes the RPM of the engine to increase.
This increase of RPM decreases when the transmission finally shifts into gear. Depending on how loose the transmission band is, this can be very noticeable when shifting.
The slipping into gear only gets worse. Every time that your transmission shifts causes more and more damage to the band causing the condition to get worse.
If you notice your transmission slipping it is time to get it to a reputable dealer or even check an online automotive service manual to see if your transmission band is adjustable.
Can a loose transmission band be adjusted
While some transmission bands cannot be adjusted, others can be adjusted by a qualified mechanic.
Even if transmission bands are adjustable this is an adjustment left to transmission professionals. The process of adjusting a transmission band is complicated and takes some time to complete.
First the transmission valve body must be removed, once this is done you can access the adjustment for the bands. A torque procedure is then completed to ensure that the correct torque is placed on the band. Once this is done a lock nut ensures that the adjustment does not loosen over time.
The transmission valve body is then re-installed, transmission is filled with new fluid and test driven to ensure that it now shifts correctly.
What can happen if I ignore a faulty transmission band
As mentioned above, if you ignore the problem of a loose transmission band it will only cause more severe issues. If you do not adjust the band as soon as symptoms are noticed the band will continue to wear faster.
This wear can cause debris to travel all throughout the transmission resulting in failure of costly internal parts that could have otherwise been avoided if taken to a service center as soon as a problem is noticed. If you do not you could have to rebuild or replace the transmission.
While transmission problems can be difficult to repair. Keeping a close watch on symptoms of a loose transmission band will allow you to identify what is wrong with your vehicle’s transmission and get it repaired as soon as possible. Ensuring you have none of these symptoms is an important thing to check before going on a road trip.
Saving you not only money but also the dreaded roadside breakdown caused by simple symptoms of loose transmission bands.
