drive coupling repair
One very common problem
is with the drive couplings on the Bachmann range of locomotives.
Symptoms for this fault are that the locomotive will run OK at slow
speeds but as the speed increases the motor spins faster and the loco
actually slows down. Initial symptoms could be that this fault occurs
in only one direction. There may also be a screeching sound as the
engine slows down with more power being applied.
The fault is caused by a plastic
sleeve that takes the drive from the motor or driveshaft into the final
drive assembly. This small plastic sleeve is a push fit over a splined
shaft. The plastic sleeve cracks, opens slightly and can no longer grip
the splined shaft to transmit the drive power. The plastic sleeve simply
spins on the splined shaft.
are a series of pictures showing a repair of the drive unit from a faulty
Bachmann Class 221 DMU 221122 Virgin Trains model.
This is the drive unit of
the Bachmann Class 221 DMU 221122 Virgin Trains model. It contains the
motor, drive assemblies and the electrical power pick-up.
With the body removed you
can see the motor in the centre of the chassis and the two power bogies.
Two driveshafts with universal joints take the drive from the motor
to the power bogies.
This is a
close up showing the grey plastic drive coupling in location at the
top of the drive bogie. This grey plastic sleeve connects the drive
shaft at the bottom of the picture to the worm gear shaft in the drive
bogie. It also acts as a universal joint allowing the bogie to rotate
and float a little.
There's the fault. The grey
plastic moulding has clearly cracked and no longer grips the steel driveshaft
to transmit the drive power. It will grip at slow speeds but slips at
higher motor speeds. This causes the train to go slower and not faster
as more power is applied. Also, there is a screeching sound as the plastic
moulding spins on the splines of the steel shaft.
...and just in case you thought
this is an easy repair. This is the bogie drive unit taken apart to
carry out the necessary work.
At least it's a great opportunity
to clean and re-grease everything.