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Drum brakes
I’ve worked on my Meritor disk brakes Front & Tag But I have not touched my drive axle drum brakes. I need to adjust them and check them out. What is the procedure for adjusting drum brakes?
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5 Replies
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Your coach if it has manual adjustment slack adjusters first block the wheels so the coach will not roll. Release the parking brake.
On the face of the slack adjuster should be an adjusting nut that has a round collar around it. Push the collar down with a 9/16 box end wrench and with the collar pushed down tighten the nut by turning clockwise. As the nut is tightened the brake shoes will expand until they are tight against the brake drum at which point you should back off about 1/3 turn. When you remove the wrench make sure the collar springs back and locks the adjusting nut.
If you can have someone apply the service brakes while you measure the push rod travel on the brake chamber I believe the travel should be 1 1/4″ or less. I do not know that for sure so verify that distance. If it is the specified distance or less you are properly adjusted.
If the coach has automatic slack adjusters you should not touch them. But if you insist the procedure is exactly the same except you are lifting a flat washer to free up the square adjuster. Travel should be the same. If the travel is within the specified range they do not need adjusting regardless of if they are manual or automatic adjusting.
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Art, there are a lot of youtube videos and/or you can call Meritor to get the manual # that applies to your brakes.
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For our older Meritor cam drum brakes and slack adjusters:
http://graphicvillage.org/meritor/mm4.pdf
and for our older Meritor Air disc brakes:
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Today I pulled the Tag wheels off and did maintenance on Meritor ADB1560 disk brakes, pulled pins cleaned and lubed with slick 50 lube with ptef then clay base grease on caliper. tightened pads to rotors greased rear fitting to power shaft, then outer fitting till grease came out popet valve in middle then back off slack adjuster all the way grease comes out valve, once backed off tighten back to rotors then back off 3/4 turn, check free play, it was 1 inch tightened up a little over 1/4 turn then its 3/4 of a inch free play. equals a little less then a half off a turn. Then I decided to service drive axle drum brakes, I tried to turn slack adjusters were pretty gummed up so I removed both slack adjusters cleaned them up so you could see them again, cleaned shaft up put syn grease on shaft and reinstalled them lubbed pins and greased 4 fittings 2 s cam and power shaft and slack adjuster. Tightened to contact shoes to drum then came back 3/4 turn, 1inch free play came up 1/4 turn to should be 0.5 to 0.625 inch free play, then had my wife push pedal at 95 psi in tank and it was about 1.5 inch movement. Called it good. Matt from Meritor was very helpful.
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For those coaches with automatic slack adjusters periodically measuring push rod travel to insure it is within specs is all that is required. On manual slack adjusters I found backing off from a tight brake about 1/4 to 1/3 turn consistently provided the correct travel so that was all I did at each service interval.
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