General Question about Auto Slack Adjusters

Yes there is a manual adjustment that you should set, because the auto adjustor works about 50% of the time and depends on amount of grease that you put in it. The adjustor is set to tighten up and not back off with out removing the lock. Tighten down until you get the DOT prescribed travel on the slack adjuster.

 

There is no adjustment on the slack to change how much it adjust automatically. If it is adjusting too much or too little something else is wrong.

 

Some automatic slacks do have external mounts that triggers the adjustment. The Gunite brand general use the angle of the push rod coming out of the brake can as a way of triggering adjustment. Worn S-cam bushings and/or the brake can not properly installed can lead to improper auto adjust. Gunite auto slacks have the 2 arms that connect to the pushrod clevis. The second smaller arm with the rubber boot is the one that senses the angle and triggers adjustment. Sorry but I couldn't find a good pic.

The Haldex brand use a fixed point rod to trigger the adjustment. Wear on the rod or its brackets can thrown off adjustment. I have also see the adjustment pin move a tad or bend with a frozen slack adjuster. I have attached a pic of the Haldex unit and one can clearly see the gold colored bracket that is part of the adjustment trigger. The slot on the far bottom left is where the stationary pin goes through to tell the slack when to adjust.

Check out the manufacturers websites for service manuals and you will be surprised how easy they are to setup and inspect. Many slacks are replaced even though they are just improperly setup or need re-adjsuting.