Technical insight: The importance of prop shafts

Technical Insight Prop Shafts

Imperial Engineering shares a list of routine prop shaft checks to help you keep this vital component of the drivetrain good condition

Prop shafts, often called drive shafts, transmit the rotational torque from the gearbox and engine to the drive axle, while allowing for relative movement between the gearbox and drive axle. These components can vary in length and incorporate a universal joint (UJ) at each end. Some units also feature a splined sliding joint to compensate for relative movement.

These components are subject to torsion and stress, so they need to handle all the forces applied. UJs consist of two hinges that are oriented 90° apart, which are connected by a cross shaft.

Prop shafts require regular checks, although intervals can vary depending on bus usage. In general, it is recommended that buses operating in cities have prop shaft checks at intervals not exceeding 25,000km, or every three months.

Bus parts specialist Imperial Engineering recommends the following routine prop shaft checks:

  • Check the main tube body of the prop shaft for damage and ensure the balance weights are present and not loose. Any dents, major damage or missing weights could cause excessive vibration through the drive train and lead to premature bearing failures or increased wear on the UJs. Significant dents around the sliding spline joint could reduce the effective stroke
  • Inspect the two main yokes on the UJs to ensure they align. Misalignment reduces the available range of movement the prop shaft can deliver
  • Ensure all the main mounting flange bolt assemblies are tight. Signs of rust around the bolt assembly could indicate a loose bolt/nut assembly
  • Check the UJ assemblies for excess rust coming from the bearing caps/seals, as this could be a sign of water ingress and reduced lubrication to the roller bearings, that can lead to failure
  • Test the UJs for excess movement. From the underside of the vehicle, lift the UJ to ensure there is no excess movement. This needs to be carried out at both ends of the prop shaft. Also check for excess movement on the sliding splined joint
  • Some UJ assemblies are sealed units and do not have the capability for re-greasing, while others have grease nipples to allow for this. Clean the grease nipple and apply the correct specification grease until it emerges from around the seals of the roller bearings
  • Some prop shafts have a protection cover over the splined sliding connection. Ensure the cover is present and has no damage, which could allow contamination to enter
  • If the prop shaft has been removed for any reason, it is good practice to inspect the rear axle and gearbox drive flange bearings for excess play. Check the mounting flanges of the prop shaft, gearbox and rear axle for any corrosion build-up and damage.

As one of the UKs leading PSV prop shaft suppliers and providers of prop shaft repairs, Imperial Engineering is an authorised distributor for Dana Spicer Driveshaft and GKN Driveline. Alongside brand-new OEM units, we also offer a comprehensive range of prop shaft parts, including universal joints.

Imperial Engineering is pleased to support operators with technical advice and guidance. For further information, please call 01992 634255, email enquiries@imperialengineering.co.uk or visit www.imperialengineering.co.uk