- Subject: Transmission goes to neutral on shift to fourth gear
- Unit: 4F27E/FN4A-EL
- Vehicle Applications: Ford, Mazda
- Essential Reading: Rebuilder, Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
A frequent call we receive on ATSG’s technical hotline with the 4F27E (FN4A-EL) transmission is a neutralizing shift going into fourth gear. The reason why it is such a frequent complaint is that there are several causes of this malfunction.
One of those causes is a failed solenoid-body bonded gasket leaking off SSA feed pressure (Figure 1). As a result, the 3-4 shift valve does not stroke properly, and this causes the band to be released at the same time the forward clutch is released, producing the neutral condition with just the direct clutches being applied.
Likewise, a mechanically failed shift solenoid A (SSD with Mazda) can produce the same complaint for the same reason (figures 2 and 3).
The third cause is a failed servo (Figure 4) preventing application of the band after the forward clutch has been released.
With three possibilities causing a neutral shift into fourth gear, yet another possible cause was masked. This fourth reason for not having fourth gear is a foreign piece of material blocking SSE oil from stroking the solenoid shift valve in the valve body. When Gerald Campbell originally discovered this on the technical hotline it was still elusive to us as the technician said, “All I could find is what looked like a sliver of silicone the size of a hair stuck in an orifice,” yet we didn’t know which orifice in the spacer plate he was referring to.
Eventually Gerald ran into this again with Ernie Garza from Victor Transmission in San Fernando, Calif., who was willing to take a picture for us. His foreign debris (Figure 5) was much larger than a sliver of hair we had heard about earlier. So we were concerned and wondered, was this the same orifice or a different one, and how could such a large piece of debris find itself in such a location?
Nevertheless, this problem of orifice-blocking debris persisted on our phone lines, giving us the opportunity to confirm that this was the orifice being blocked. Donald Holliday from Covington Auto in Louisiana had not only provided for us verification that this was the orifice being blocked but also sent us the debris (Figure 6) that blocked the orifice in his spacer plate. It was stringy rubber material balled up as if it were pieces from a skinny rubber band that had traveled through the hydraulic circuit, collected in a pocket and fused together. Where this material came from is as much a mystery as where it is found. One guess is that it is coming from the release side of the band’s bonded servo, where there may be excessive “rubber flashing” that separates from the piston and travels through the circuit in small pieces. But the one mystery that can be solved is what actually happens when this orifice in the spacer plate is blocked.
Figure 7 is a hydraulic schematic of third gear showing how solenoid pressure from shift solenoid E is used to release the band servo, apply the direct clutch and stroke the solenoid shift valve in preparation for the 3-4 shift.
Figure 8 is a hydraulic schematic of a normal 3-4 shift during which the forward clutch is released and servo-release pressure is exhausted, allowing apply pressure to apply the band.
Figure 9 is a hydraulic schematic showing what occurs during the 3-4 shift when foreign debris has blocked shift-solenoid E pressure from stroking the solenoid shift valve. Pressure from shift solenoid A will now stroke the clutch-control valve rather than the 3-4 shift valve, exhausting direct-clutch oil and releasing the band. This equates to total neutral, as there is not even one apply or holding element in play.
It is obvious that this type of complaint will occur if the valve body was never disassembled for cleaning. And in some instances that decision is made when the transmission appears to be clean enough to do so. We have seen where the unit is in for repairs for this very reason, a neutralizing going into fourth. Since the solenoid body molded gasket, shift solenoid 2 and the servo are the three most commonly known reasons for this complaint, they are replaced without the valve body ever being disassembled. With now knowing yet another cause, you may be able to say to this 4F-27-3 Neutral, “Take a hike!”