They are not new but some people are still having problems with them. Automatic slack adjusters on air brake equipped vehicles are only automatic if they are working properly. The only way to find out if they are working properly is to include them in a good daily pre-trip inspection. And, besides, it is the law; it is the driver’s responsibility to ensure that the brakes are in adjustment even if it is not the driver’s responsibility to adjust the brakes manually.
Automatic adjusters are very easy to adjust. There is no need for any tools. Simply make a full brake application of 90-100psi and hold that brake application for 2 – 3 seconds so that the air pressure in the brake chamber has a chance to build up to that of the application. Pumping the brakes several times and not holding a full application may not achieve the same result as the air pressure will not have a chance to get to the required 90-100psi in the brake chamber which will cause the adjusting mechanism to work.
The more often full hard brake applications are made the better chance that the brakes will be in adjustment. If the auto slacks don’t appear to be adjusting, then it is time to take the truck to the mechanic who should be trained how to recognize the problem. Manually adjusting automatic slack adjusters just covers up another problem.