BMW i3 2014-present Drivetrain Bolt Torque Specifications

Using the correct torque ensures proper clamping force. Under-torquing can lead to bolts loosening, causing component failure, excessive wear, and potential safety hazards. Over-torquing can stretch or break bolts, damage threads, and compromise the integrity of the drivetrain components. For example, a wheel bearing carrier bolt torqued incorrectly could lead to a bearing failure and wheel detachment.

Overtightening can deform the bolt or the mating surface, weaken the bolt's clamping force through stretch, and make future removal difficult. In extreme cases, it can cause bolt failure resulting in costly repairs and potentially dangerous situations. Example: overtightening the axle shaft bolt could damage the spline or fracture the axle.

Generally, it's recommended to replace torque-to-yield (TTY) bolts, which are commonly found in drivetrain applications, after each use. TTY bolts are designed to stretch when tightened, and their clamping force may be compromised if reused. Always refer to the BMW repair manual or parts catalog for specific bolt reuse recommendations. Some non-TTY bolts can be reused if they are inspected for damage and show no signs of thread wear. For example, hub bolts should be replaced, but control arm bolts could be reused after inspection.

You'll need a calibrated torque wrench of the appropriate range for the specific bolt you're tightening. You may also need sockets, extensions, and potentially adapters to access the bolts. Digital torque wrenches are highly accurate, but a good quality click-type torque wrench is sufficient for most applications. For example, a 1/2-inch drive torque wrench is suitable for axle and suspension components, while a 3/8-inch drive may be used for smaller bolts.

Nm (Newton-meter) and lb-ft (pound-foot) are units of torque. Nm is the standard unit in the metric system, while lb-ft is commonly used in the imperial system. 1 lb-ft is approximately equal to 1.356 Nm. Always ensure your torque wrench is set to the correct unit, and the specified torque value for that unit, to achieve the required clamping force. Using the wrong unit will lead to incorrect torque application. Example: an i3 axle bolt requiring 100 Nm should be tightened to approximately 74 ft-lb.