TM 5-2420-230-24-1
Spicer Speciality Axle Division - Technical Publications
SECTION 21
INSTALLATION AND USE OF CROSS AXLE AND THIRD DIFFERENTIAL LOCKS
Installation Recommendations and Instructions
21.1
Warning light system
Each diff. lock is fitted with a switch which shall be connected directly to an individual warning lamp in
the drivers cab, to indicate when the lock is fully engaged. Each light shall be of the double bulb type or
incorporate a bulb checking feature to avoid an incorrect warning.
Differential locks on steer drive axles
Differential locks are not recommended on steer drive axles. This is because, when a locked axle is
steered, the required speed difference between off side and near side wheels is prevented, causing a
wind-up of torque in the shafts, gears and dogs. This can cause the tyres to skid, a phenomenon which
will affect vehicle control. Moreover, it greatly increases the torque required to turn the steering swivels.
If indeed, a customer does demand a diff. lock on a steer drive axle, then it must be emphasised that
this shoiuld be engaged only when wheel slippage has immobilised the vehicle and that it must be
disengaged within a few seconds of recovery.
Instructions for vehicle operators
21.2
Warnings
Diff. locks are for use only under conditions where adhesion between tyres and ground is extremely low.
They must be disengaged as soon as conditions permit.
Prolonged running with locks engaged can (due mainly to steering), promote wind-up between off side.
and near side shafts, gears and dogs. This can lead to breakage of components.
If a diff. lock is fitted to a steer drive axle, it should only be engaged when wheel slippage has
immobilised the vehicle and it must be disengaged within a few seconds of recovery.
Engagement
IMPORTANT :- DIFF. LOCKS SHALL ONLY BE ENGAGED WHILST THE VEHICLE IS
STATIONARY.
i)
On approaching low adhesion terrain :-
The vehicle shall be stopped and diff. lock switches operated. If dogs do not engage
fully, as witnessed by the warning lights, the vehicle shall be driven and manoevered
slowly until full engagement is achieved.
ii)
When vehicle is immobilized due to wheel spin.
Any wheel spin must be terminated prior to attempting diff. lock engagement.
Diff lock switches shall be operated. If the dogs do not engage fully, as witnessed by the
warning lights, the transmission shall be allowed to rotate until full engagement is
achieved.
Driving shall not be resumed until full engagement has been verified by each respective
warning light.
Disengagement
Release pressure from operating chamber. It is then essential that the vehicle is
manoevered slowly to ensure full disengagement of diff. lock dogs and relieve
wind-up.
Manual No. 1785 Issue A
Page No.C24
Spicer Speciality Axle Division
J-88
