Also an engineer here, so no reason why we can't overthink it. I think we can both agree that if we saw some present this as a solution to the parking brake we would fire them =P. I'm just worried because the youtube video shows both sides going out. Not the whole assembly moving to the right (in the direction of the lever) The drum part of the rotor shows clear indication the parking brake was touching.
it seems all the forces are pushing the assmebely to the direction of travel of the lever. There is not enough return forces to push both sides of the assemply out. Unless the return force is meant to be the force exerted on the inside drum.
[MENTION=937]TechWrench[/MENTION] what do you mean opposite the rear one? In this case, the pad in the direction of travel of the lever is working, its just the trailing shoe which is not being pushed outwards. I am going to place the rotor on 50% and apply the parking brake to see I can demonstrate proper operation.
My car has been on jacks since Saturday =/
I will try to be more specific, but bear with me if my terminology is not exactly correct....
First, so we are both on the same page, I hope, the left and right side parking brake assys, are mirror images of each other. When I speak of leading or trailing shoe, I am talking about (leading) the shoe closest to the front of the vehicle (either side), and the trailing shoe is the one closest to the rear of the vehicle (either side). At the top center of the brake assy., there is a fixed post (anchor) that both leading and trailing shoes rest against, and the two upper return springs pull the top of each shoe against this post. At the bottom of each set of shoes is the star wheel adjuster that is connected to each shoe and held in place by one spring that pulls the bottom of each shoe toward the other one and holds the adjuster in place. The two pins with springs and cup washers are designed to hold each shoe in position against the backing plate. They have nothing directly to do with actuating the parking brake. The parking brake shoe lever is connected to the top of the trailing shoe via a fixed pin, which it can pivot on. There is also a parking brake shoe strut with a compression spring that rests in slots in the top of each shoe, both leading and trailing, and also fits into a slot on the parking brake lever on the trailing shoe. The two upper return springs also serve to keep both shoes securely on the parking brake shoe strut. When the parking brake cable is pulled, it pulls the bottom of the parking brake shoe lever forward, toward the front of the vehicle. Because the lever is connected to the parking brake strut below the pin on the upper trailing shoe, it causes the top of the trailing shoe to push out toward the drum surface. ( The next few statements are specific to the left/drivers side assy., it would be the opposite for the passenger side)
When the pressure from the lever pushes the trailing shoe against the brake drum, and the vehicle is rolling forward, the trailing shoe tries to rotate counter clockwise, but because the top of it is against the anchor, it can't move. Once the trailing shoe has contacted the drum surface, the action of the parking brake lever, using the parking brake strut, then forces the leading shoe out toward the drum surface. With both leading and trailing shoes now in contact with the drum surface, and held there by the action of the lever and strut, braking force is applied. When the lever is released, the upper springs pull the shoes back into the anchor, to the rest position. When you are backing up, the leading shoe contacts the drum and because the top of the shoe is at the anchor, the force travels around the circle of shoes to force the trailing shoe outward and against the drum. When you are standing still, the lever still forces both shoes outward to the drum surface to apply braking force and hopefully hold the vehicle in place. In its simplest form, the entire lever and strut assy. is designed to make the two shoes expand the friction material surface circle to meet the drum surface circle. All the star wheel adjuster does is separate the two lower ends of each shoe enough to make the friction circle just a bit smaller than the drum circle, so the drum can turn without dragging. And, as the friction material wears off the shoes, reducing the diameter of the circle, adjusting the star wheel makes up for the loss of friction material.
I am hoping this makes sense. It is always a lot easier to explain this to someone, when I have them right with me, looking at the exposed assembly as we go.
