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ADB Brakes adjustment?
I’ve been servicing the air disk brakes (ADB) Front and tags clean replace pins lube calipers with Meritor clay base grease. Last is the adjustment, I watched an older Rockwell video about the brakes, I do have the Yellow templates and they talk about (free stroke) set with template by hand with pry bar set at 3/4 to 1 inch of (free stroke) , and then they talk about (adjusted chamber stroke), with pushing on pedal, they talk about chamber size to determine adjustment, don’t really get it, What is a good way to adjust brakes???
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4 Replies
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Assuming you have the Meritor with self adjusting brakes in the literature they are kind of fussy (probably written by a lawyer) and say not ot adjust them unless you are qualified or certified.
If they are manual adjustable it is a whole different world.
I have adjusted both and it is a similar process. In manual adjustable, use the wrench (9/16″) and press down on the outer sleeve with the wrench. Once the sleeve is depressed the adjusting hex will rotate. Turn the wrench tightening the brake (combo brakes have to be released for brake adjustments) and when the brake is tight, back off 1/4 to 1/3 turn.
For the self adjusting brakes you use a flat bladed screw driver or similar tool (I used a small putty knife) to lift the flat sheet metal brake lock and then using a square ratchet similar to what you might use on a refrigerant valve rotate the adjuster to tighten the brake and back it off about 1/3 turn.
Then have someone apply the brakes and measure travel to insure it is within the specified travel range for the brake chamber size. In no case should you ever have so much travel the red mark on the brake rod is visible.
You can check travel manually by using a tool or whatever you can get to apply leverage to the slack adjuster arm. Rotate the arm and as stated the maximum travel should be around 3/4″. Using the brakes with air the travel is going to be far greater than trying to do it manually unless you have a lot of strength or a very long lever arm.
There is an alternative way to both verify and adjust self adjusting brake slack adjusters. Make sure the slack adjuster has more than an acceptable travel. Remove the service brake hose from the chamber. Using shop air and an air blow gun with a rubber tip shoot air into the air hose hole or fitting to apply the brake. Do that repeatedly to allow the slack adjuster to self adjust. If it does not self adjust it needs to be replaced.
That’s the Reader’s Digest version. If you get into it you will understand.
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This info is in the Meritor ADB mx manual mm4m, section 11 “Adjust The Brakes”, starting on p.50 of 68.
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When I adjusted after greasing and replacing pins with lube I tightened slack adjusters to rotor backed off 3/4 turn and free stroke is 3/4 inch, but before everything I tightened slack adjuster and it was a tad over 1/2 turn backed off. Isn’t it true the auto slack adjusters will self adjust so If they are a little loose it will selfadjust??
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If they are self adjusting they should re-adjust as needed to the correct point. If you are concerned back them off and either pump the brakes or give shots of supply air to the chamber to verify they are in fact returning to the correct point.
I’ve never been that patient after doing brake work, but after a few thousand miles I would check travel of the brake chamber rod either manually or by having my wife step on the brakes while I measured travel.
So far I have never had any issues with failed self adjusters.
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