Technically Speaking
- Author: Wayne Colonna, Technical Editor
On occasions technicians may find themselves fighting a loss of line-pressure rise with a GF4A-EL transaxle. The transmission has been unplugged and line pressure still does not rise, verifying that there is, in fact, an internal transmission concern. The pressure-control solenoid has been replaced, the pump and spool valve have been inspected and determined to be in proper working order, and the pan has not been pushed up into the newly installed filter.
The valve body is removed, and the pressure-regulator valve also looks good. At this time you consult a set of hydraulic schematics and discover that there is a pressure-modifier valve in the pressure-control system (see Figure 1). Consulting a picture of all the valve locations and their identifications reveals that nowhere in the breakdown is this valve identified in any way – an oversight that has puzzled many for years.
Figure 2 provides the location of this valve line-up, which can be identified easily by the adjusting screw in the end plug (see Figure 3). (This adjusting screw usually is adjusted at the factory to a depth of about 0.012 inch from the surface of the plug. Over-adjustment of the screw has been known to cause uncomfortable coast-downshift clunks). Should this pressure-modifier valve be stuck or the bore worn, there will be no line rise. So be sure to update the manual in your library with the identification of this valve and its location.
Another manual update that would be good to make concerns the F4EAT transaxle. The 2-3 shift valve and the bypass valve are side by side near the inlet port of the valve body as shown in Figure 4. The identifications of these valves have been switched in the manual, and this error can lead to a problem of no 2-3 upshift after overhaul.
The reason for this is that many technicians peg the bypass valve to allow for a firmer 2-3 shift. This works with the G4A-EL, the GF4A-EL and the F4EAT transaxles alike. A technician who is unaware of the mislabeling of the valves in F4EAT valve-body information can unknowingly peg the 2-3 shift valve, preventing the 2-3 shift from taking place. One way to remember the correct valve is that the bypass valve is closer to the inlet and the 2-3 shift valve is the larger of the two.
