Know Your Transmission Brake
The transmission brake can become ineffective through wear, oil contamination or a stretched cable. Trevor Cuthbert shows how to keep it on top form
Trevor Cuthbert takes a brief look at variations of transfer gearbox and transmission brake types
Land Rover has used a transmission drum brake on all utility models since the first Land Rover in 1948. This type of handbrake – or emergency brake – was also used on Range Rover and Discovery from their introduction. While the size, specification and method of operation have varied over the years, the general principle of operation has remained the same. The transmission drum brake operates by two brake shoes expanding apart within a brake drum, by operation of a handbrake cable, to create rubbing or friction with the drum. This impedes or stops the rotation of the brake drum, which is directly connected inline with the propeller shafts – preventing the road wheels from turning.
The friction material on the brake shoes wears with use and an adjusting mechanism compensates for this wear up to a point. However, when the brake shoes have worn to a point where there is no further adjustment available, the handbrake will not operate correctly, so the transmission brake will require a service.
The rear output seal on the transfer gearbox can also fail, allowing transmission oil onto the friction surface, which reduces the efficiency of the material, resulting in a defective handbrake. Likewise, mechanical wear of the operating mechanism and stretching of the handbrake cable can also mean it is time to carry out a service. TYPES OF TRANSMISSION BRAKE Just as the principle of operation of the transmission brake has remained the same, the basic design and configuration of the transfer gearbox has changed little, over the years. Transfer gearboxes, from different Land Rover models, can have different final drive gear ratios and different methods of taking speedometer drive. There are also differences in how the handbrake cable operates the transmission brake – from more elaborate external operation linkages, to the later direct entry cable found on later models. Here is a brief look at variations of transfer gearbox and transmission brake types.