Usage:
776 Tractors;
777 Trucks
A hydraulic accumulator with a nitrogen charge is used in the transmission control circuit of 766 Tractors and 777 Trucks. The purpose of the accumulator is to control pressure pulsations (changes) from the pump during operation at low rpm. This keeps a smooth, even pressure in the circuit for good stability of valve operation.
To be sure the accumulator operates correctly, a new recommendation is made to check the nitrogen charge pressure every 1000 SMU (Service Meter Units), and adjust if necessary. This can be done at each oil change interval, and is in addition to checks made during transmission exchange or reconditioning.
Procedures to test and adjust accumulator pressure are shown on Pages 71 and 72 of the Service Manual Module "Systems Operation - Testing And Adjusting", Form SENR7158-02. A 7S5437 Nitrogen Charging Group and 5P2963 Charging Adapter will be needed. The correct charge pressure is 2760 ± 69 kPa (400 ± 10 psi) at 21°C (70°F).
The new recommendation is to be used for all 776 Tractors 14H1-Up and 777 Trucks 84A1-Up. Make a note of this information in Maintenance (Lubrication and Maintenance) Guides for these machines until revisions are complete.