The FSM tells us that, beyond some minor adjustment as to engagement and electrical connections from and to the switch, the unit should be changed as a non serviceable unit. Wonderful!.... 20 or 30 or 40 years ago but not now.
Having a weak or inop unit on your car can be a pain. It was for me on my 73 Town & Country and my most recent car; a 78 NYB.
Both would work only with the aid of my right foot and both had trouble keeping the set speed. Both also had their diaphragms replaced or repaired to no avail. Both were replaced with operable units and are working fine now. So, taking the deadest unit I had in my collection, I decided to take it apart to see what else could be wrong...
After removing the unit from the car and taking off the diaphragm cover and diaphragm, there is a round cover with three small screws that covers the guts.
The top winding element is the sensor/transducer for the position of the soft steel rod and magnet that run through it to the vacuum source valve (flap really) at the top. When you push the set button it energizes this coil and opens the vacuum source valve by pulling down the soft steel “L” shaped rod down at the set position establishing the mechanical “memory”.
That rod moving through the transducer is driven by a nineteenth century centrifugally driven governor powered by the transmission cable. This governor/actuator also allows the unit to be powered only beyond a certain point. Very clever switch indeed.
Below it is the vacuum control and dump valve that is electrically modulated by the above.
The rod that moves in and out is driven by the diaphragm position; modulating the vacuum source valve, regardless of position.
The rest is a collection of clockwork springs and counter springs that look and are delicate.
This diaphragm is pretty much shot after many heat cycles over the years.
Not all the faults are obvious.
What becomes obvious is that vacuum control for a semi working unit may be the problem beyond the leaking diaphragm. You can see that I changed the manifold filter at some point in the past to keep dirt out of the mechanism.
The gear driven governor and actuator. Showing almost no wear and working perfectly.
Side view of the governor and drive assembly. The seal is necessary as this is part of the overall vacuum chamber. Any leaks along the edge would weaken the vacuum chambers ability to work the diaphragm in pulling the throttle cable.
A look down into the unit side of the drive reveals the switch connected indirectly to the driven governor/actuator which is in direct line with the rod moving through the transducer. Got it so far? Good!
Ok... you will notice you can see the vacuum control/dump valve and that it has a seal. Carefully pushing back on it allows the seal to be removed... it was my suspected source of an additional leak into the overall unit. It’s made of cork... go figure.
The vacuum control/dump valve is held down by the internal cover only.
I think I got this now.
Having a weak or inop unit on your car can be a pain. It was for me on my 73 Town & Country and my most recent car; a 78 NYB.
Both would work only with the aid of my right foot and both had trouble keeping the set speed. Both also had their diaphragms replaced or repaired to no avail. Both were replaced with operable units and are working fine now. So, taking the deadest unit I had in my collection, I decided to take it apart to see what else could be wrong...
After removing the unit from the car and taking off the diaphragm cover and diaphragm, there is a round cover with three small screws that covers the guts.
The top winding element is the sensor/transducer for the position of the soft steel rod and magnet that run through it to the vacuum source valve (flap really) at the top. When you push the set button it energizes this coil and opens the vacuum source valve by pulling down the soft steel “L” shaped rod down at the set position establishing the mechanical “memory”.
That rod moving through the transducer is driven by a nineteenth century centrifugally driven governor powered by the transmission cable. This governor/actuator also allows the unit to be powered only beyond a certain point. Very clever switch indeed.
Below it is the vacuum control and dump valve that is electrically modulated by the above.
The rod that moves in and out is driven by the diaphragm position; modulating the vacuum source valve, regardless of position.
The rest is a collection of clockwork springs and counter springs that look and are delicate.
This diaphragm is pretty much shot after many heat cycles over the years.
Not all the faults are obvious.
What becomes obvious is that vacuum control for a semi working unit may be the problem beyond the leaking diaphragm. You can see that I changed the manifold filter at some point in the past to keep dirt out of the mechanism.
The gear driven governor and actuator. Showing almost no wear and working perfectly.
Side view of the governor and drive assembly. The seal is necessary as this is part of the overall vacuum chamber. Any leaks along the edge would weaken the vacuum chambers ability to work the diaphragm in pulling the throttle cable.
A look down into the unit side of the drive reveals the switch connected indirectly to the driven governor/actuator which is in direct line with the rod moving through the transducer. Got it so far? Good!
Ok... you will notice you can see the vacuum control/dump valve and that it has a seal. Carefully pushing back on it allows the seal to be removed... it was my suspected source of an additional leak into the overall unit. It’s made of cork... go figure.
The vacuum control/dump valve is held down by the internal cover only.
I think I got this now.
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