Re: 1951 200 Vacuum Wiper Motor

Posted by HH56 On 2023/4/28 9:10:26

Not sure exactly what you mean but nothing in the motor holds vacuum when it is off. The slider valve on top of the motor operated by the wire cable prevents vacuum from entering from the engine hose connection on the passenger side of the motor when it is turned off. On the other side of the valve the rest of the motor is open to air. The sliding valve covers different port openings but when off, only the park position port gets vacuum. Valve and paddle in park position should both be sealing tightly preventing a vacuum leak to any of the other ports or to the outside.

When you turn motor on the valve slides. It closes the park port to vacuum then uncovers the main passage into the motor. Vacuum is allowed to enter motor where it is immediately passed to a second internal valve which directs the vacuum to one side of the paddle. Paddle then starts moving. This second valve also allows the other side of the paddle to be open to air so it can be free to move as vacuum pulls it to one side. As the paddle nears the end of its travel in the first direction a mechanism operated by the paddle switches the internal valve. Vacuum is redirected to the formerly open side of the paddle and it can start moving the opposite direction. At the same time the internal valve switched vacuum sides it opened the first side to air so the paddle could move. This back and forth action repeats as long as the motor is on. The main port the slider valve uncovers when you turn the motor on is actually a thin slot and motor speed is somewhat controlled by how much of the slot the slider valve uncovers so more or less vacuum can enter. When the valve slides to off again the main port closes and park port connects to vacuum so paddle is forced past its normal operating sweep range to pull the blades down to the chrome molding. When the paddle reaches park position it closes the port which should prevent any leaks as the motor sits.

On motors used from around 48 to 53 there is a second hose connection located on the drivers side of the motor. That connection will be just sitting empty unless the optional windshield washer is installed. When the operator knob is turned opposite the direction needed to turn the wiper motor on there will be spring tension felt. Turning that direction and holding the knob against the spring tension causes the sliding valve to move a small amount to the other side of the off position in order to uncover another port and allow vacuum to reach that second hose connection to operate the washer.