The responsibility of the Pontiac drum brake wheel cylinder is to use the hydraulic pressure it is supplied and push out against the brake shoes. It is this braking action that makes it possible for the friction to be created. The drum brake wheel cylinder has two pistons that are forced outward from its center when the hydraulic pressure is being applied to it. They push out in opposite directions with each one applying pressure to a separate drum brake shoe. The shoes are then forced against the drum's surface which slows the Pontiac down. The only non-metal components of this brake part are the polymer seals on the pistons used to hold the hydraulic fluid in the drum brake wheel cylinders. It is these seals that do fail in time and require the entire component to be in need of replacement. A driver will notice something is wrong when one of these seals in the drum brake wheel cylinder ruptures by the way the brakes react to pressure being applied to them. There will be a significant lack of stopping power of your Pontiac because the hydraulic fluid is coating the inside of the drum preventing it. The level of pressure is also limited and cannot be maintained. This leaking Pontiac drum brake wheel cylinder will also make its mark on the pavement by creating a puddle of hydraulic fluid there. The location of the drum brake wheel cylinder is in the center upper section of the brake plate that is only held in place by 2 bolts. Once the brake shoes are taken off, it can be easily removed and replaced. Remember the brake line has been in place for some time so care should be taken when removing it on your Pontiac.