Advice: Turntable Maintenance

During winter, the roads are generally wetter than in other seasons. Consequently, more road grime and mud gets flung around the workings of a truck.

Needless to say, this road grime and mud mixing with grease under the turntable forming a thick gunk substance that inhibits the turntable's operation, causing the locking mechanism to stick and bind.

One of the most compelling indications a turntable has a problem is when a driver notes that the turntable is hard to release on their daily trip sheet.

Technically-minded fleet operations managers will heed this sign as a warning. That’s because if the turntable is hard to release, it will be equally hard to lock up properly when coupling.

When uncoupling, depending on the turntable brand, a driver can use the truck's horsepower to force the jaws to open. However, when it comes to coupling up a trailer, it is the free movement of the turntable's mechanism combined with the tension and timing provided by the springs to get the jaws to lock correctly.

When the mechanism under the turntable is hindered by a build-up of grime and grease or corrosion, the coupling and uncoupling operation will become problematic.

However, regular cleaning turntable maintenance will reduce grease and gunk build up. In fact, some turntable manufacturers suggest switching to a thinner 90-weight oil during extended cold weather operation.

When the turntable mechanism is covered in gobs of grease, a thorough inspection may be not possible. Needless to say, an extensive steam cleaning around the working parts of the turntable will certainly make inspecting the turntable far easier.

The exact inspection requirements vary depending on the model and brand of the turntable, but in essence, you're searching for any damage to the top plate, condition of the release handle, checking for slack in the jaws and proper operation of the jaws.

In terms of the turntable's preventive maintenance process, much of it is inspection, diagnostics and adjustment. For example, when checking things like the release handle, make sure the springs are all in place and adequately tensioned and jaw and locks are clean and lubricated.

It is important to note that while adjustment procedures differ across brands and models, the allowable tolerance of clearance does not.

NHVR Roadside inspectors will sideline a truck with any more than 12mm of fore and aft movement between the turntable top plate and the trailer skid plate. The majority of turntable manufacturers recommend about 1.6mm free play around the kingpin.

However, excessive play between the truck and trailer will be felt like an uncomfortable bang or clunk during gear changes and when launching. Continued use of a truck with extreme wear in the turntable will eventually wear the throat of the fifth wheel.

As mentioned earlier, corrosion may develop on bare metal springs, so inspect them vigilantly and replace them as necessary.

Most manufacturers’ operating instructions have no description for wear on the springs, other than to say if they are functioning appropriately, then they're doing their job.

Trailer winches can easily damage or bend release handles. In some situations, a damaged handle could hinder the locking mechanism.

An adequately lubricated turntable top plate will deliver optimum operation.

Subsequently, a layer of grease is essential for free movement between the prime mover and trailer. However, it's often misapplied. If too thin a grease film is applied, this will cause more significant wear of the turntable.

On the other hand, too much grease is a more common problem and brings its own set of issues. Old residual grease contains dirt and dust that accumulates over thousands of kilometres; contaminated grease lessens its effectiveness.

Most manufactures recommend cleaning the old grease from the top plate before applying new grease. Once the top plate is cleaned thoroughly, apply a small bead of grease evenly in a back-and-forth motion starting the top of the edge (front) of the turntable.

Increase the bead size towards the rear of the turntable because the trailer skid plate will push grease forward during the coupling process. Remember, too much grease is unnecessarily messy and wasteful. Furthermore, it will do you no favours at the end of the day other than getting stuck on diff housings and brake boosters.

Most turntable handbooks advise that you don't need a tremendous amount of grease, other than ensuring the grease pockets in the top plate are full. However, for optimum lubrication and service life, manufacturers recommend using greases formulated specifically for turntable applications.

Thin greases will wear away quickly, especially during wet conditions, while an excessively thick grease layer may cause clumping, especially in the cold. Greases formulated with heavier base oils, high solids content and extreme pressure (EP) additive package are the preferred lubricant to attain adequate film thickness,

You will find that most manufacturers suggest water-resistant lithium or moly-base grease. But consult the specific maintenance manual for your turntable for the correct recommended lubricant.

Inspect greaseless liners for cracks and damage. Replace liners that are worn excessively or broken; it's important to note that both liners should be replaced simultaneously if one liner is damaged.

Manufacturers recommend that liners be replaced every 300,000 kilometres in highway applications and every 200,000 kilometres for severe duty applications or less than 3mm thickness at the top of the liner.

Do not overtighten the liner screwing screws, and the recommended torque setting is 45Nm.

You mustn't grease the top surface of the greaseless liners. However, greaseless turntables do require that you grease the jaw.

For the correct lubrication specifications to suit your turntable or if you’re unsure, refer to the owner's manual.