Another verification, my 89 f250 came with a c6.
A c6 is a "automatic" transmission. But it needs information on when to shift. It gets this information from the governor inside the tranny that measures road speed, and from the vacuum modulator(the thing with the black band) that gives it information on throttle position.
On a gas engine, those engines naturally have vacuum and it varies with throttle position and engine load. This is perfect for the vacuum modulator on the back of the tranny. But a diesel doesn't have vacuum, only a external vacuum pump driven by a belt. So Ford invented what they are calling the "VRV". It's just a variable valve hooked to the throttle shaft. They run the vacuum supply from the pump to the VRV, and then another line from the VRV to the modulator on the back of the tranny. As you move the throttle, the amount of vacuum sent to the tranny is changed, giving it info on when to shift.
Lots of vacuum(this would be the case for the line hooked up directly) means the throttle is not open very much. So the tranny's program assumes there is very little power demand from the engine, so it shifts soft and very quickly up to 3rd gear. When you open the throttle up, there will be very little vacuum going to the tranny. In this mode it assumes you are demanding power from the engine. It raises the line pressure in the tranny, giving a firmer shift and delaying the shifts to let the engine rev up and get things going. It juggles the vacuum applied to the modulator along with the road speed from the governor to make these decisions.
A c6 is a "automatic" transmission. But it needs information on when to shift. It gets this information from the governor inside the tranny that measures road speed, and from the vacuum modulator(the thing with the black band) that gives it information on throttle position.
On a gas engine, those engines naturally have vacuum and it varies with throttle position and engine load. This is perfect for the vacuum modulator on the back of the tranny. But a diesel doesn't have vacuum, only a external vacuum pump driven by a belt. So Ford invented what they are calling the "VRV". It's just a variable valve hooked to the throttle shaft. They run the vacuum supply from the pump to the VRV, and then another line from the VRV to the modulator on the back of the tranny. As you move the throttle, the amount of vacuum sent to the tranny is changed, giving it info on when to shift.
Lots of vacuum(this would be the case for the line hooked up directly) means the throttle is not open very much. So the tranny's program assumes there is very little power demand from the engine, so it shifts soft and very quickly up to 3rd gear. When you open the throttle up, there will be very little vacuum going to the tranny. In this mode it assumes you are demanding power from the engine. It raises the line pressure in the tranny, giving a firmer shift and delaying the shifts to let the engine rev up and get things going. It juggles the vacuum applied to the modulator along with the road speed from the governor to make these decisions.
