TM-5-3805-254-14-P-2

TRUCK, DUMP, 20 TON, 6X4, ON-OFF HIGHWAY 71,000 GVW, IHC MODEL F-5070 (CCE)

TECHNICAL MANUAL; OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, GENERAL SUPPORT AND DEPT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS INFORMATION AND SUPPLEMENTAL MAINTENANCE INSTRUCTIONS)

JUNE 1980

TM-5-3805-254-14-P-2 - Page 698 of 894

TRUCK SERVICE MANUAL

DESCRIPTION AND OPERATION

Para 2-26/2-27

r. Automatic Downshifts

(1)

Automatic downshifts, like upshifts, are

controlled by rear governor and modulator pressures.

Downshifts occur in sequence as rear governor pressure

and/or modulator pressures decrease.

Low modulator

pressure (open throttle) will hasten the downshift; high

modulator pressure (closed throttle) will delay downshifts

(2)

In any automatic downshift, the shift signal

valve acts first.

This exhausts the shift signal holding the

relay valve downward.

The relay valve then moves

upward, exhausting the applied clutch and applying the

clutch for the next lower gear.

s. Downshift and Reverse

Inhibiting

(1)

Inherent in the system, as a result of valve

areas and pressure calibrations, is a means for

preventing downshifts at a too high vehicle speed or a

reverse shift at an excessive forward speed.

(2)

Progressive downshifts occur because the

regulated hold pressure is calibrated, along with the

valve areas, to shift the signal valves downward against

rear governor pressure only when the governor pressure

decreases to a value corresponding to a safe downshift

speed.

Thus, if speed is too great, rear governor

pressure is sufficient

to hold the shift signal valve

upward against hold pressure.

As rear governor

pressure decreases, the shift signal valves move

downward in sequence.

691

TRANSMISSION