AFL和AFL

The right-hand ends of all three valves also receive the Actuator Feed Oil. It is shown in blue here but it comes from the same source as the orange. This blue side oil is either exhausted or allowed to build pressure by the solenoids. That pressure acts on a much larger spool diameter than the same pressure shown in orange, so it wins the battle. If the pressure is above a certain point, it will overcome spring force as well and then stroke the valve to the left.

没有tice that Solenoid A does double duty by directing AFL (blue) pressure to both the 1-2 and 3-4 shift valves to stroke them left. Notice also that Solenoid B does double duty by stroking the 2-3 shift valve left but also helping the spring force the 1-2 valve back to the right, even if solenoid A is on.

In this system, line pressure is always available for the shift valve to send to a clutch. If the shift valve is not in the intended position, it feeds the wrong clutch. For example, if AFL pressure was too low to overcome any of the shift valve springs, all the valves would be to the right. That happens to be the desired valve position for second gear with OD range selected, where both solenoids are allowed to exhaust off AFL pressure. The result of the low pressure in this case would be a 2nd gear start.

AFL oil pressure is an offspring of line pressure. Like line pressure, it is not a constant pressure but one that rises and falls. It is limited to a maximum regulated pressure of 115 psi in high line situations and will be less than line under all circumstances. AFL-related problems would most likely begin to occur in light throttle or coast situations when line is already low. When AFL pressure drops to the 45-48 psi range, problems begin to appear.

Lets look at this deteriorating condition. AFL pressure is present but it is getting dangerously low. What could be the first appearance of an issue? Another Fourth Lost. Here’s why. (SeeFigure 2)。1-2换档阀“蓝侧”区域优势与3-4换档阀区域的优势几乎相同，但它必须克服比3-4更轻的弹簧。它可以在较低的压力下克服光弹簧，并且不会是两个不能冲进其阀的第一个。

The springs on the 2-3 and 3-4 are very similar and the force needed to overcome either is very close. The “blue side” area advantage of the 2-3 is bigger than the 3-4 so at the same pressure, it applies more force to overcome the spring. The first valve to creep back as pressure begins to get critically low is 3-4. When it starts to move to the right, 4th clutch feed is diminished. When it moves too far to the right, 4th clutch feed is shut down. Another Fourth Lost.

Think about this the next time you get the unit that falls out of 4th or has no 4th at all. Consider it also if you do not yet have any 4th gear complaints but the teardown reveals 4th clutch distress. First look at the familiar 4th gear issues as you always did. Then remember AFL and AFL.