I have an 89 f350 4x4 dually and my drum brakes seem to basically back off the adjusters by them selves. I adjust them and it stops great for a while and then it starts to slowly deteriorate until i have no rear brakes.

I have done this 4 times now so I am sure its actually backing of and its not just worn out.

Is there some sort of auto matic adjuster that is not working or something? I have herd of something that tightens when you back up, but I am not experienced with drums.

 

check to see if the right adjuster is on the left side and the left adjuster is on the right. They have a lh and rh threads and could have been swapped prior to you working on them. If thats the case, they will do as you describe while driving.

 

Like mentioned, once you get the drums off, carefully operate the rachet on the adjusters. Note what way it pulls/rotates and see if the threads are correct. If someone got them mixed around during a previous brake job, it could be loosening them(instead of tightening).

 

This is exactly why all new trucks come with disk rear brakes.

 

As others have mentioned, take the drums off and make sure that the adjusters are operating correctly and on the correct wheels. If you pull on the adjusting cable and release it should advance the adjuster one or two clicks. With the drums and wheels back on, and everything working properly, you can also adjust the brakes by slamming on the brakes in reverse.

Get a close adjustment with the star wheel. Then to finish the adjustment, carefully back up in reverse and get up to about 10 MPH than slam on the brakes and let the truck come to a complete stop before releasing the pedal. Do this several times and your brakes should self-adust to the proper position. They will not over adjust if working properly.