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Internal Wind-off Mechanism on Spring Brake Actuators

We can't stress enough the importance of understanding the internal wind-off mechanism on spring brake actuators to correctly fit these in the vehicle. Andrew Blower, Sales Manager at EBS has discussed this with Transport Operator and has provided tips on avoiding fitment and warranty problems.

Andrew Blower, UK sales manager at air brake specialist EBS, explores the topic of internal wind-off mechanism spring brake actuators

Spring brake chambers are a fundamental part of the wheel end braking system, transforming the energy of compressed air into a mechanical movement with such high forces as to bring the vehicle to a safe stop, as well as being able to keep the brake in a parked position.

A regular pattern we see is that users do not fully understand the workings within the internal wind-off units or how to properly set these during the fitment process, along with the ‘dos and don’ts’. One ‘don’t’ we regularly see evidence of is the use of air tools to set the wind-off mechanism; our units clearly state that air tools must not be used for this, but they still are.

So that we can educate the users of this product type and assist in avoiding further vehicle downtime and costs, our engineers at EBS have compiled an explanation of the internal mechanism process during each stage, and what the result will be when these steps aren’t followed.

Full vehicle guidelines and health and safety procedures must be followed when replacing items of this nature and to ensure the vehicle is in a safe and secure manner in order to carry the work out safely. Never attempt to remove the brake chamber’s body.

Two common issues we encounter on a regular basis come down to the fitment process when this style of actuator is being replaced, these being:

The wind-off bolt mechanism not being turned in the correct manner until the ‘button’ is fully retracted into the wind-off bolt end (see right-hand diagram).

The mechanism being over-torqued (usually from the use of air tools during fitment) and subsequently causing a breakage of the connection between the piston and spring, rendering the unit unfit for use and voiding all warranty.

EBS supplies all internal wind-off brake chambers in a pre-fitment state known as ‘caged’, with the push button exposed from the wind-off mechanism nut, and these are how they will reach the user.

The left-hand diagram shows the pre-fitment state (the lower body is not shown in the diagrams so that the internal workings are visible).

During the fitment process the winding mechanism is turned, with air pressure of around 6.5Bar applied to port 12, in the correct direction (as is clearly stated on the instructional label affixed to the units EBS supply) which begins to move the protective plate allowing the spring to actuate the piston. Do not use air tools to perform this.

When the mechanism has entirely uncaged, the button on the winding mechanism’s nut will have fully retracted inside the mechanism itself (right-hand diagram) and is now ready to fit to the vehicle.

Once the chamber is fitted to the vehicle and the handbrake is applied, this will release air from the chamber, and the piston will actuate.

The EBS Aftermarket Group holds one of the largest ranges of brake chambers, available with a two-year warranty, manufactured to OEM specification and fully inspected by EBS’s own team of QC engineers.

More information on EBS brake chambers, as well as over 35 other product ranges, are available at the website.

www.ebs.co.uk