So let’s see what happens if shift solenoid D (SSD) is stuck open ( Figure 3). This allows line pressure to flow to the reverse clutch and SSB pressure to the low/reverse clutch.
AUTOMATIC TRANSMISSION SHIFT SOLENOID MANUAL
One of the first things we see is that line pressure from the manual valve flows through the clutch control valve to shift the low/reverse shift valve to the reverse position. It is time to revisit the oil-circuit diagram. Remember, we said earlier that the problem did not affect any of the forward upshifts. If the solenoid is stuck closed then the unit would not have 2nd and 4th gears. The low/reverse shift valve is what allows the solenoid to perform double duty. One problem with this is that in the forward ranges SSB applies the 2-4 servo. Obviously, the low/reverse clutch would not apply and we would have no reverse. So let’s take a look at what happens if SSB is stuck closed. Next, if we look at an oil-circuit diagram for reverse ( Figure 2), we see that shift solenoid B (SSB) is sending solenoid pressure to the low/reverse clutch. This allows the reduction brake to apply even if SSF is not working. There is a case passage that feeds reverse-clutch pressure to the secondary valve body to move the 4-5 shift valve. There is one problem with this theory, though. In the forward ranges, the reduction brake is what gives you engine braking. 2 one-way clutch would hold the secondary sun gear instead of the reduction brake. First through 4th gears would work fine because the No. If SSF is stuck closed the 4-5 shift valve would not move, the reduction brake would not come on and there would be no reverse. At first glance it seems like a no-brainer. The 4-5 shift valve in turn routes line pressure to either the reduction brake in reverse and 1st through 4th gears or the direct clutch in 5th. SSF is on the secondary valve body and controls the position of the 4-5 shift valve. If you look at the solenoid application chart in Figure 1, you’ll find that only shift solenoid F (SSF) is on in the reverse position. Looking for more technical transmission info like this? Be sure to sign up for the Transmission Digest newsletter to have it delivered to your inbox once a week.
Shift solenoids D, E and F are normally closed (do not allow pressure to flow when de-energized) on/off-type solenoids. Shift solenoids A, B and C are normally open (pressure flows through when they’re de-energized) duty-cycle-type solenoids. The FNR5 uses six shift solenoids to control upshifts and downshifts and TCC apply.
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