Motorhome Automatic Slack Adjusters - Periodic Maintenance Required?

Brian Keys was a Country Coach motorcoach expert during his tenure at the defunct Country Coach, LLC Country Coach brand motorcoach manufacturing company. He shared his product knowledge in articles and at rallies held across the U.S. This article was authored in 2002 and shared in Country Coach LLC’s former print publication, Country Coach Destinations. I share it here for its technical value to owners of the older Country Coach motorcoaches still traveling America’s roads today. Obviously, with time some technical information may be outdated.  
Note: Country Coach Corporation, a service and consignment coach sales business in Junction City Oregon, currently produces a monthy epublication. You may learn more online at www.countrycoach.com.

 

 

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Is Maintenance Required on My Motorcoach's Automatic Slack Adjusters

 by Brian Keys

 

Q) My chassis user's guide indicates that my coach is equipped with Automatic Slack Adjusters. Since they are "automatic", is there anything that I need to do in the way of periodic maintenance?

A) That's a great question, because the answer is not as obvious as it may seem. As you may already know, in an air brake system, the Automatic Slack Adjuster (ASA) is basically a lever that transforms energy provided by the coach's air system into torque. This torque, or twisting power, applies the vehicle brake linings against the brake drums (or rotors in the case of disc brakes). Additionally, as its name would indicate, the ASA is the point in the brake system where slack between the brake linings and the drums or rotors is monitored and corrected.

This is necessary because as the brake linings wear due to normal usage, the slack adjuster must twist farther in order to obtain the same application force between the brake linings and the drums or rotors. At some point in this process, if no adjustment were to be made, you would find yourself pushing ever harder on your brake pedal, even as your coach became more difficult to stop. So ASA's are designed to make constant, small adjustments as the brake linings wear, thereby maintaining optimum brake adjustment. Before the advent of ASA's, slack adjusters had to be checked and adjusted manually and at regular intervals based on mileage in order to avoid this situation. So then, ASA's have made the old manual slack adjuster inspection and adjustment requirements obsolete, right? Well, actually, yes, with some qualification. With a properly engineered brake system like the one on your coach, no manual adjustment of your ASA's should be necessary until normal brake wear makes a standard brake re-line necessary. It is still a good idea to have these components checked at each chassis service. The most effective and straightforward test of proper ASA adjustment is the Chamber Power Stroke Measurement Test. This straightforward test takes just a few minutes, and will confirm that your ASA's are adjusting properly. Any qualified chassis shop will be familiar with the tolerances recommended by various brake manufacturers. If your coach is a 2000 model year or newer, the coach User's Guide should contain an Appendix section which lists the recommended tolerances for your vehicle's brake system. Of course, regular lubrication of the ASA's, along with a minor inspection of the brake system at the intervals outlined in your coach User's Guide is a necessary part of your overall chassis maintenance program.