Fault diagnosismanual gearbox
Note: It is sometimes difficult to decide whether it is worthwhile removing and dismantling the gearbox for a fault which may be nothing more than a minor irritant. Gearboxes which howl, or where the synchromesh can be 'beaten' by a quick gear change, may continue to perform for a long time in this state. A wom gearbox usually needs a complete rebuild to eliminate noise because the various gears, if re-aligned on new bearings, will continue to howl when different wearing surfaces are presented to each other.
The decision to overhaul, therefore, must be considered with regard to time and money available, relative to the degree of noise or malfunction that the driver can tolerate.
Gearbox noisy in neutralWorn transfer gears or idler gear bearing (noise stops when clutch pedal depressed)
Layshaft bearings worn
Gearbox noisy in all gearsOne or both of above faults General wear
Gearbox noisy in one particular gearWorn, chipped or damaged gear teeth
Gearbox jumps out of gear on drive or overrunDetent balls and springs worn
Coupling dogs worn
Selector forks worn or rods loose
Worn synchro hubs or baulk rings
Crunching or crashing when changing gearClutch fault (see Chapter 5)
Worn baulk rings or synchro hubs
Difficulty in engaging gearClutch fault (see Chapter 5)
Gearchange linkage worn, loose or maladjusted