September 30, 2005
In Ford 4F50N, AX4N, AX4S and AXODE transmissions, main pressure valve regulates line by pushing the pump slide into a decrease or limiting position. The instability of the valve, combined with the slide return spring, causes pressure spikes in the decrease (PC) oil circuit of more than 500 psi. When the inboard end of the pressure regulator valve wears, the CBY or bypass oil cannot flow past the regulator valve. This causes delayed engagements and reduced converter fill and lube oil flow. In the 1998 and later AX4Ns, Ford changed the spool lengths on the pressure regulator valves at the converter/lube feed area. This change was to allow the converter circuit to be fed sooner. In the pre-1998 design, the converter/lube circuit is completely closed at high line pressure. Sonnax oversized pressure regulator valve kit 96206-10K mimics the later OE design to prevent converter/lube-related problems at high line pressure.
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