Shift Pointers
- Author: Mike Souza
Delayed or No Engagement in Ford 5R55N/W/S Transmission
At ATSG we have received several calls on the 5R55N/W/S transmission in the new Lincoln LS, Jaguar, Ford Explorer or Mountaineer concerning a complaint of delayed or no engagement. The condition occurs most often during first morning startup, under extreme cold-temperature conditions, and the transmission may engage if the throttle is snapped wide open.
This complaint may be caused by a sticking flow-control valve in the line-pressure relief-valve assembly resulting from a groove worn into the assembly sleeve. It also can result from an excessive oil-flow leak if there is not a proper seal between the very thin assembly-sleeve O-ring and the pump plate.
First thought might be to check for converter drain-back. This procedure is not as easily done as on most vehicles because of the absence of a dipstick. You’ll have to raise the vehicle on a lift to check fluid level by removing the oil-level check plug in the center of the pan/sump, as shown in the fluid-check procedure in figures 1 and 2 taken from the ATSG 5R55N and W/S bench manual.
Some rebuilders have said that the valve was completely stuck in the open position upon transmission disassembly. The drawing in Figure 3 from ATSG tech bulletin 04-26 along with the photos in figures 4 through 7 will show the line-pressure relief-valve assembly and the area of the sleeve that becomes worn, causing a ridge where the flow-control valve becomes lodged.
Figure 8 is a diagram from the bench manual showing the location of the pressure-relief-valve assembly and O-ring. The O-ring is very thin and barely extends above the surface of the pump body, which is a potential area for a leak. Adding an A4LD pump-bolt washer in the pocket of the pump under the sleeve would help raise the sleeve to compress the O-ring more tightly, creating a better seal. Caution: Be careful not to raise the sleeve above the pump surface, only the O-ring.
As demonstrated in the partial oil schematic from the tech bulletin in Figure 9, if the valve were to stick in the open position, or the oil flow leaked past the O-ring, the oil pressure would flow in the path of least resistance and return to the suction side of the pump. Notice that an orifice controls the oil on the spring side of the valve. During initial start-up (especially when the oil is cold and flow is slower) the valve will move toward the spring (which has very little tension) very easily, causing the valve to lodge on the ridge at the end of the sleeve.
If a pressure gauge were attached to either pressure tap (see Figures 10 and 11), the reading would be 40 psi or lower. On some occasions, snapping the throttle wide open will free the valve, regaining oil pressure and transmission engagement.
Although this complaint, sometimes referred to as “morning sickness,” is most common during an extremely cold first morning startup, it has been noted on some occasions to happen intermittently during coast-down stops under average temperature readings. When I say average, I’m not speaking about the temperatures here in south Florida, which are never average. Temperatures above freezing, say 40-55°, would be average during the colder months in most other states. (Although I don’t miss Massachusetts during those months, I have to say I do miss being in New England during the summer months here in Miami.)
At the time of this printing, I don’t know of any aftermarket or OE source for the relief-valve assembly separately. You can buy a complete pump assembly from Ford or several aftermarket hard-parts suppliers. You could rob a relief-valve assembly from another pump if you happened to have one. Keep in mind, though, that it might be in the same shape.
Aftermarket manufacturers are aware of the problem and are working on a replacement relief-valve assembly that should be available soon. So if one of these units arrives at your shop and the sleeve does not show excessive wear patterns, you may want to make sure that the O-ring is not misplaced and add an A4LD pump washer to create a better seal as a precaution.
Mike Souza is a technical-hotline specialist with the Automatic Transmission Service Group (ATSG).
