Ariens HVZ 915085-2350 Service Manual download pdf (Page 23)

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7.1 PRINCIPLES OF OPERATION

The hydro transmission is a self contained unit

designed for the transfer and control of power. It

provides an infinitely variable speed range between

zero and maximum in both forward and reverse modes

of operation. See the manufacturer’s manual for a

hydraulic schematic.

This transaxle uses a variable displacement pump with

a maximum displacement of 10cc per revolution, and

motor with a fixed displacement of 10cc per revolution.

The variable displacement pump features a trunnion

mounted swashplate with a direct-proportional

displacement control. Reversing the direction of the

swashplate reverses the flow of oil from the pump and

thus reverses the direction of the motor output rotation.

The pump and motor are of the axial piston design and

utilize spherical nosed pistons which are held against a

thrust race by internal compression springs.

The transmission has a self contained fluid supply and

an internal filter. The fluid is forced through the filter by

a positive “head” on the fluid in the housing/expansion

tank with an assist by the negative pressure created in

the pump pistons as they operate.

The check valves in the center section control the

make-up flow of the fluid to the low pressure side of the

loop.

A cam style, block lifting bypass permits moving the

vehicle for a short distance at a maximum of 2 m.p.h.

(3.2 Km/h) without starting the engine.

7.2 HYDRO TRANSMISSION

TROUBLESHOOTING

The following troubleshooting chart is to be used to

isolate hydro transmission problems and give possible

causes and corrective action responses.

The troubleshooting key is generic and can be used for

several types of transmissions. Use only those

possible causes and corrective actions that apply to the

unit.

NOTE: In many cases, problems with the transmission

are not related to a defective transaxle, but are caused

by slipping drive belts, partially engaged bypass

valves, and loose or damaged control linkages. Be

sure to perform all operational checks and adjustments

outlines in this section before assuming the pump is

malfunctioning. The troubleshooting checklist is an aid

for determining the cause of operational problems.

SECTION 7 - DRIVE TRAIN

WARNING: Actuating the bypass will result in

the loss of hydrostatic braking capacity. The

machine must be stationary on a level surface

and in neutral when actuating the bypass.

TRANSMISSION TROUBLESHOOTING

Problem Possible Cause Corrective Action

Operates in only one

direction

Control linkage bent or out of adjustment Repair or replace linkage

Drive belt slipping or pulley damaged Repair or replace drive belt or pulley

Air trapped in hydraulic system Purge hydraulic system

Shift rod grooves worn Replace shift rods

Mower does not drive/

track straight

Steering handles out of adjustment Adjust steering handles. See Adjusting the Unit to

Track Straight for adjustment procedure.

Vehicle tires improperly inflated See Specifications, for recommended tire

pressures

Control linkage bent or out of adjustment Repair or replace linkage

Bypass assembly sticking Repair or replace bypass

Unit is noisy Oil level low or contaminated oil Fill to proper level or change oil

Excessive loading Reduce loading

Loose parts Repair or replace loose parts

Bypass assembly sticking Repair or replace linkage

Air trapped in hydraulic system Purge hydraulic system

Metallic pieces or foreign objects in unit Repair or replace transmission

Cooling fan damaged Repair or replace cooling fan

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