Manual gearbox fault
10.2.5 Manual gearbox fault
Symptom Possible causes
Suggested action
diagnosis table 2
or faults Clutch Clutch
Possible cause slipping
Renew
Symptom
worn out Noisy in a particular gear Damaged gear Adjustment
Worn bearing incorrect
Adjust or check
(with engine running)
auto-adjuster
Oil contamination
Rectify oil leak –
Noisy in neutral
Input shaft bearings worn (goes
clutch may also need
(with engine running)
away when clutch is pushed down?)
to be renewed
Lack of lubricating oil Clutch release bearing worn (gets
worse when clutch is pushed down?) of gear
Jumps out Gearbox
Gearbox may
detent fault
require overhaul
Difficult to engage gears Clutch problem Noisy when
Gear linkage worn or not adjusted changing gear
Synchromesh
Gearbox may
worn
require overhaul
correctly
Rapid knocking Driveshaft CV
Work synchromesh units noise when
Renew or lubricate
Lack of lubrication cornering
joints worn or
joint
without
Gear linkage worn or not adjusted lubrication
Jumps out of gear
correctly
Ensure gaiter is in
Worn selector forks
place and in good
Detent not working
Weak synchromesh units Whining Wheel bearing Renew
condition
Lack of lubrication noise
Vibration
worn Worn bearings Other Investigate and
Mountings loose bearings
renew if possible
Gaskets leaking Difficult to
Oil leaks
Worn seals change gear
Clutch out
Adjust or check
of adjustment
auto-adjuster
Transmission systems 253
10.2.6 Clutch faults diagnosis
10.3 Automatic
table
transmission
Symptom Possible cause
10.3.1 Introduction
No pedal Broken cable resistance
Air in hydraulic system
An automatic gearbox contains special devices
Hydraulic seals worn
that automatically provide various gear ratios, as
Release bearing or fork broken
they are needed. Most automatic gearboxes have
Diaphragm spring broken
three or four forward gears and reverse. Instead
Clutch does As above
of a gearstick, the driver moves a lever called a
not disengage Disc sticking in gearbox splines
selector. Most automatic gearboxes now have
Disc sticking to flywheel Faulty pressure plate
selector positions for park, neutral, reverse, drive, 2
and 1 (or 3, 2 and 1 in some cases). The engine will
Clutch slip Incorrect adjustment
Worn disc linings
only start if the selector is in either the park or neu-
Contaminated linings (oil or grease)
tral position. In park, the drive shaft is locked so
Faulty pressure plate
that the drive wheels cannot move. It is now quite
Judder when Contaminated linings (oil or grease)
common when the engine is running to be able to
engaging Worn disc linings
move the selector out of park only if you are press-
Distorted or worn pressure plate
ing the brake pedal. This is a very good safety fea-
Engine mountings worn, loose or broken Clutch disc hub splines worn
ture as it prevents sudden movement of the vehicle.
For ordinary driving, the driver moves the
Noisy Broken components
operation Release bearing seized
selector to the drive position. The transmission
Disc cushioning springs broken
starts out in the lowest gear and automatically
Snatching Disc cushioning springs broken
shifts into higher gears as the car picks up speed.
Operating mechanism sticking (lubrication?)
The driver can use the lower positions of the gear- box for going up or down steep hills or driving through mud or snow. When in position 3, 2, or 1,
10.2.7 Drive shafts fault
the gearbox will not change above the lowest gear
diagnosis table
specified.
Symptom Possible cause
10.3.2 Torque converter
Vibration Incorrect alignment of propshaft joints Worn universal or CV joints
operation
Bent shaft
The torque converter is a device that almost all
Mountings worn
automatic transmissions now use. It delivers power
Grease leaking Gaiters split or clips loose
from the engine to the gearbox like a basic fluid
Knocking noises Dry joints
flywheel but also increases the torque when the car
Worn CV joints (gets worse on tight corners)
begins to move. The torque converter resembles a large doughnut sliced in half. One half, called the pump impeller, is bolted to the drive plate or fly-