IRS Axles and Drop Axles with Thin Drop Plates causing Problems

Thin Drop plates on IRS and Drop Axles are continuing to cause problems.

Drop plates with a thickness of 25mm are breaking during shock loading events. Couplemate and Alko use 32mm drop plates which effectively results in less damage to IRS and drop axle builds.

Shock loading events occur unexpectedly when, for example, the trailer jumps a roundabout curb or when the caravan is forced off the road, climbing a gutter.

The trailer that suffered the broken drop plate in the above image was a 2000kg tandem trailer. The problem is magnified substantially on 4.5t vehicle.

Forensic Investigation

There may be a more sinister, unseen reason for this drop plate breakage.

Did you notice the bearing buddy that replaced the dust cap? We suspected the owner inadvertently overfilled the bearing buddy.

As a result of overfilling the bearing buddy, grease was expelled out of the back grease seal and into the mechanical backing plate cavity.

This, in turn, caused brake shoe contaminated, which in turn caused brake failure.

So was the brake failure the cause of the accident or was it the broken drop plate the cause of the accident?

In our opinion, excess grease from the bearing buddy escapes through the rear seal once the hub is at speed and pressurised. The heat caused an increase in the grease viscosity thereby causing contamination of the brake shoes.

As a result of contamination, the brake shoes became ineffective.

At this point, we can only theorise that a sway event occurred which a brake event failed to rectify sway before the wheel hit the gutter thereby causing shock loading on to the drop plate, breaking it.

Bearing Buddy

Bearing buddies are designed for unbraked, disc brakes and hydraulic braked trailer axles. Should bearing buddies be overfilled on this type of axle, the excess grease is expelled to the ground of highway. Brake pads are not generally subject to contamination on this type of axle assembly.

In our opinion, bearing buddies can cause grease contamination of brake shoes when overfilled.

Couplemate has concluded that bearing buddies are unsafe to be used in conjunction with drums brakes and should be immediately replaced with conventional or grommeted grease caps.

50mm Square x 4″ Drop Axle

How Can Drop Plate breakages be Minimised

The hollow electric drop axle assembly in the right-hand image has a 32mm thick drop plate.

Couplemate uses 32mm plates because we found too many examples of 25mm plate breakages.

Sturdy drop plates cannot prevent grease from escaping into brake cavities, but they can avoid breakages of equipment.

This type of assembly carries loads up to 1450kg per axle.

© Stephen Wotherspoon, 14th April 2020