What makes you think they're over-adjusting? If you back the adjusters down, the shoes are going to have to move further so you WILL have a low pedal and the parking brake will run out of cable. The shoes have to move for the adjuster to do its thing, and the shoes can only move if they aren't out far enough.
If one of the drums is getting tight, check for a sticking parking brake cable that isn't fully releasing. If you find that either shoe is not contacting the large anchor pin, the shoes will be able to rotate a little each time you apply the brakes while you're moving. That can activate the self adjuster. There must also be a little free play in the parking brake strut rod when you push it against the anti-rattle spring.
Sunday, April 10th, 2011 AT 1:11 AM