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Maintenance Series Part # 1 – Shimming the Clutch and Brake

Quite often WPT encounters clients in the field that don’t quite recognize the importance of correct clearances and the shimming. Some customers are just unaware of the need to adjust the shim stack when it comes to new friction verses used friction. Shimming is also required when conducting maintenance where other key internal clutch components are replaced.

In a Power Grip or Low Inertia unit, all the internal components have a manufacturing tolerance. When a new unit is assembled, it is shimmed to fall within a set clearance range. Each brake or clutch model has a specific operating clearance that can be found in the installation and maintenance manuals. They are also displayed on each assembly drawing. Should there ever be a difference between the manual and drawing, always defer to the drawing.

Clearance is important because the airtube actuator can only travel a certain distance before the tube starts rounding. When the airtube starts to round, this causes a surface area loss against the pressure plate. Reduced airtube surface area has a direct impact on torque capacity and may encourage extra slip time. This will impact the performance, accuracy, and generate higher internal heat levels resulting in unnecessary wear.     

When units that use an airtube for actuation are in operation, and under normal service conditions, the friction material wears and becomes thinner. To keep the set clearance range, it is possible to remove shims and thereby extend the service life. Once all shims are removed, it is time to replace the friction discs. When replacing friction discs in a unit, it is very important to add any removed shims back into the assembly and re-check the clearance.

Checking clearance is quite an easy process. Instructions can be found in the installation and maintenance manual for the unit. For additional information on determining clutch measurements, read the article, How to Measure the Operating Clearance in Your Power Grip PO Clutch.

The staff at WPT Power are always here to help, be it a WPT Power assembly or fault finding with a competitor’s compatible unit. If you or any of your maintenance team need some support, please contact WPT Power: https://wptpower.com/contact/

Written By: Brett Emson, Sales Manager Asia Pacific & Africa