244
Model Code Page
51. Brake system
1. 9. 2002
6250--8950 521 2
1. 10. 1999
B. Parking brake on tractors with HiTech Shuttle
Picture 1. Parking brake mechanism
1. Parking brake cylinder
2. Valve block on which there is a
hand brake solenoid valve
2a. Parking brake solenoid valve Y18
3. Shuttle lever (position P)
4. Hand brake cable
5. Sensor
A. Valve allows oil to flow out of ram
with a little counter pressure
In connection with HiTech Shuttl e the hand brake is con-
trolled electro---hydraulically. When the engine is running
and the shuttle lever (3) is moved to position P, hydraulic oil
pressure from the low pressure circuit is cut off in the ram
(1) (solenoid valve (2a) becomes unenergised) and the
ram spring pulls the hand brake on.
When pressure again is connected to the ram (soleno id
valve energised), pressure compresses the spring and
hand brake is released.
When t he engine is stopped (pump stops), the hand brake
comes on automatical ly with an aid o f the spring force.
If the hand brake does not disengage (engine running)
although the shuttle lever is moved to the N, R or F position
so:
--- check whether the solenoid valve (2a) is energised (mag-
netic), when the hand brake is disengaged. If not, measure
the sol enoid resistance, which should be 11---12 ohms.
--- If the solenoid is faulty, it should be replaced.
--- If the solenoid is OK, measure whether current comes up
to the solenoid connector. If not, check the solenoid wires
and co nnectors.
--- The condition of the shuttle lever switch can be tested in
the AC 5/5.2 test mode, see pages 370/10 or 371/8.
--- If the s olenoid and its wiring and the hand brake switch
areOK,thefaultcanlieinthehandbrakerelayorintheAC
5/5.2 control unit.
---IftheseareOk,thefaultcanlieinthehydraulicsystem.
Note! If the hand brake engages itself during driving, the
solenoid valve (2a) has become unenergised or low pres-
sure circuit has malfunctions.
Note! If the driving speed exceeds 2 km/h (in the beginning
of the production 4 km/h), the hand brake engagement is
prevented by relay K28 (in the lever console) .
--- a non---return valve from ser. no. K50440 incl. has been
fittedinthesystemwhichtogetherwiththeAC5.2program
modification, retards the pressure drop in the low pressure
circuit in cases that e.g. engine stops during driving (e.g.
fuel runs out). Program disengages all transmission multi---
disc clutches, if the engine stops and the driving speed
exceeds 5 km/h. In this case the parking brake cylinder
starts to brake after 15...30 seconds.
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