BMW 335i 2005-2011 Drivetrain Bolt Torque Specifications

Using a torque wrench ensures that bolts are tightened to the manufacturer's specified torque. Over-tightening can stretch or break bolts, damage components, or lead to stripping threads, while under-tightening can cause bolts to loosen, leading to component failure, noise, vibration, and potential safety risks. For example, over-tightening a driveshaft bolt might cause it to shear, while an under-tightened bolt could lead to driveline vibration and eventually failure.

Torque sequence, often used for multi-bolt connections, ensures even clamping pressure across the mating surfaces. Ignoring it can lead to warping, uneven load distribution, leaks, or premature failure. For instance, tightening the transmission bell housing bolts randomly could lead to misalignment and potential oil leaks.

Some bolts, particularly those used in critical drivetrain locations (like the flywheel or pressure plate), are designed for single use (torque-to-yield) and should be replaced after each removal. Reusing these bolts could compromise their integrity and cause failure. Check the vehicle's repair manual or parts catalog for specific recommendations. Reusing these bolts could also alter the clamp load of the component.

Lubrication can significantly affect the applied torque. Torque specifications are typically based on dry threads. If you lubricate bolts (with oil, anti-seize, etc.), the achieved clamp force will be higher than intended for the same torque, potentially leading to over-tightening. Always check the service manual and if lubrication is needed, it will specify what lubricant and what torque adjustment needs to be made.

Torque bolts are tightened to a specific torque value, while torque-to-yield bolts are tightened to a certain torque, then turned a specific additional angle. Torque-to-yield bolts stretch when tightened, creating a more precise and consistent clamping force and they must be replaced after each use. These are often used in high-stress areas.