Allison 1000 Oversize Control Main Relief Valve Number 37000-19. Fits 2000–2015 units only.
In 2000–2015 Allison 1000 / 2000 / 2400 units, wear in the control main relief valve bore can cause or contribute to reduced control main pressure to the shift solenoids and reduced A & B trim pressures. The control main relief valve limits peak control main pressure and is always active when the vehicle engine is operating. In action, the valve reacts against a stiff spring outboard using small diameter spools inboard to limit control main circuit pressure. The combination of a stiff spring and small valve spools creates significant valve side loads which can wear the valve body bore. As bore wear becomes excessive ATF is allowed to escape into the exhaust back-fill circuit or directly to the sump and critical pressure is reduced to the shift solenoids and A & B trim valves causing shift issues.
Reconditioning the bore and installing Sonnax oversize control main relief valve 37000-19 eliminates escaping oil and restores hydraulic control to the control main relief circuit.
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