adjusting brakes

Pictures would help.... Not familiar with a "locking nut" on slack adjusters.

 

Caging bolt ?

 

If you are working on automatic slack adjusters you should not have to adjust them.

If you release your brakes and give them a few good hard applications, like over 90 PSI, they will adjust themselves.

If they do not adjust themselves they will need to be replaced.

It is important to keep them greased.

 

I second the hard to the floor applications of the service brake vs slack adjusters. You will probably get them good enough until the next mechanic who has training to look them over.

 

Meritors have what looks similar to the head of a bolt, 3/4". There is a spring and a lock pawl under it. The lock pawl has a flat side and will only go in one way.
If they are not working sometimes the lock pawl has to be replaced. We normally do not mess with them as well. Just check the travel at every service and maybe snug them up a couple clicks.
Auto slacks that need constant adjustment should have a professional look at them. Incorrect brake chamber lengths will also cause them to malfunction.

 

Yes and

Yes

Also make sure the chambers are the same.

I see alot of long and standard stroke chambers on the same axle. Some roadies dont know any better or just throw on what they have it seems.

 

I think there's a small round metal ball under that spring..Be careful not to loose it..

 

That is the pawl as @BoxCarKidd stated Meritor slack.

Thread it back in. Pry out the center with a flat blade to release the locking pawl. The 5/16 square on top is the adjuster. You must advance the adjuster tight slight to get the pawl to release from its bite. Then back off.