Workhorse Auto Park parking brake “Over-Travel” explained

Workhorse Auto Park parking brake “Over-Travel” explained

One of our user sent the following:

“On my 2003 P32 chassis, the “AUTO PARK” display and the combination Brake System Warning Light / Parking Brake Indicator Light (!) are on with the Yellow Button pulled out and the shifter in Park position.  This is correct according to the Workhorse manual.  However, there is also a buzzer sounding for some reason.  Also, the (!) light stays on and the buzzer still sounds when the Yellow Button is pushed in, but they should go off according to Workhorse. Workhorse states that this indicates that the brake system needs servicing.  But if I put the shifter in Drive with the Yellow Button pushed in, both the “AUTO PARK” display and the (!) light and the buzzer go off.  What’s going on?  What needs servicing?”

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Here is our response:

As mentioned else ware on this site, a condition called “over travel.”  Explanation:  Your parking brake is a drum type brake on the driveline – – right behind the transmission.  This brake is APPLIED by a very heavy spring that is inside a hydraulic cylinder.  When the cylinder is pressurized, the piston compresses the spring.  When the pressure is removed, the spring expands, AND pulls on a cable that applies the brake.  I’ll send an illustration that portrays this action.

Under normal circumstances, when the pressure is removed and the spring expands, the piston travel is limited by the cable drawing tight as the brake shoes tighten against the drum.  So if the shoes are badly worn, or the cables too loose, the piston will travel farther than it would otherwise.  When the piston DOES travel too far (over travel), it engages a micro switch that sounds the buzzer – – thus warning you that your brake shoes need adjustment/replaced, or the cables need adjustment.  It is pretty unusual for the shoes to be worn enough to require replacement unless the brake has been dragging for some time.

Questions and comments and questions are always welcome  oldusedbear

Posted in: Category 2 - - AutoPark troubleshooting, and isolating the problem

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