What Are Fifth Wheel Top Plates?

From RVs to heavy duty class 8 tractor trailers, a towing job may not be possible without the use of a fifth wheel top plate. You probably see them while you’re driving down the road, and don’t even realize it. But what exactly is a fifth wheel top plate?

The fifth wheel top plate is the horseshoe shaped plate that is attached to the main frame of the vehicle. They consist of many internal components, such as lockjaws, springs, bushings, and a release handle, that must all work together smoothly for operation. The purpose of the fifth wheel top plate is to provide trailers and cargo a secure connection for heavy loads, if coupled correctly. If the internal components are not working properly, the truck may not be able to connect or disconnect from the trailer; or worse yet, the trailer could disconnect while driving down the road causing thousands of dollars in damage or even worse yet! Excessive movement between semi and trailer can affect the semi’s handling and could result in loss of control. That is why proper maintenance of your fifth wheel plate is essential.

Proper Maintenance of Fifth Wheel Top Plates

Proper maintenance of your fifth wheel top plate is essential to you and the cargo you haul. A top plate that has not been inspected and maintained can cause serious issues while on the road. The following 3 factors will help you get the full longevity of your fifth wheel top plate.

1. Inspect All Components
2. Lubrication
3. Rebuild Kits vs. Replacement

Inspect All Components

Top Plate Free Play

The adjustment screw plays a silent but important role on your fifth wheel top plate and could mean the difference between getting to your destination with your trailer or losing it while driving down the road. Over time, your lockjaws will wear down and loosen from the pulling weight and jerking motion of your trailer. If your lockjaws are too loose, your trailer could completely disconnect while you’re driving down the road. This happens all too often and can be easily prevented.

To prevent your trailer from disconnecting, most importantly you need to routinely inspect the top plate locking mechanism for proper play. Most manufacturers recommend free play of 0.080” but check your manufacturer specifications before tightening or loosening the adjustment screw. By tightening your adjustment screw, the lock jaws of your fifth wheel top plate will remove any excess free play between the fifth wheel top plate and the king pin on the trailer. Although it is less common, sometimes your lock jaws can become too tight and loosening the adjustment screw is needed. By loosening the adjustment screw, the lock jaws will add free play between the top plate and king pin, but most manufacturers don’t recommend having less than 0.040” of free play.

King Pin Wear

The trailer’s king pin is what locks into the fifth wheel top plate’s lockjaws to securely couple the trailer to your truck. This king pin will wear down with time, creating more free play with your top plate. The king pin of the trailer needs to be inspected for damage or too much wear before every hook-up.

It is not recommended to repair damaged or worn king pins. The king pin should be replaced to ensure there are no issues when connecting. If there is a king pin that is thought to be too worn, use a king pin gauge to check the kingpin for excessive wear limits. If the king pin is damaged or worn beyond the manufacturer’s specifications, replace the king pin.

Lubrication

Keeping your fifth wheel top plate lubricated has many benefits by itself. Proper lubrication of your fifth wheel plate will allow for your trailer to move smoothly and freely while on the road. Unless you have a no-lube fifth wheel, insufficient lubrication can damage the top plate, locking mechanism and trailer kingpin and irregularly wear steer tires. It may seem like an easy task to add some grease on your fifth wheel top plate, but too little and it can cause greater wear.

To lubricate your fifth wheel top plate correctly, you want to remove the old, built up grease layer that is pre-existing. Next, fill the dips, known as grease pockets, with a liberal amount of grease intended for fifth wheel applications. After filling the grease pockets, you now want to apply a thin layer of grease over the whole top plate, with any excess grease being moved towards the back two-thirds of the fifth wheel plate. Once you couple a trailer, the grease will be pushed forward helping to spread the lubricant across the mating surfaces.

Other surfaces on the fifth wheel top plate will also need to be lubricated on a routine basis. Grease zerks can be found around the outside and just under the top plate. Make sure to apply grease to these areas, but do not over lubricate. Over-lubrication can lead to locking components sticking, especially in cold weather.

To help avoid lubrication, new technology has been developed to ease the maintenance requests of fifth wheel top plates. The NoLube Plate allows you to continuously work without the worry of ever greasing your top plate.

Rebuild Kit vs. Replacement

Rebuilding or replacing your fifth wheel top plate can be determined by many factors. Rebuild kits are a great option for plates that are still in good condition, but before you choose to go with a rebuild kit, you will want to inspect all components closely for any underlying factors or damage that may stop you from using a rebuild kit. Top plates that have some wear but still show good grease grooves and with no damage are usually a good fit for using a top plate rebuild kit.

Fifth wheel top plates are a piece of safety equipment that if too worn or damaged, they may not hold the new parts from a rebuild kit. If your top plate is damaged, or just too old and worn out, a new replacement fifth wheel top plate is in order. Replacing your top plate can be a quick change on most machines and offer you the peace of mind knowing your new top plate would be under warranty.

There are many factors to help make the decision between a replacement and a rebuild kit. Comparing the cost of a rebuild kit to the purchasing of a replacement top plate, the two really are not too far off of one another. The cost of the rebuild kits and replacement plates will depend on many factors including the brand, model, and special features that the top plate may have. By the time you also factor in any labor for the rebuild kit, the replacement and rebuild kit cost almost equals out.

Wheelco’s Fifth Wheel Top Plate Recommendation

Proper maintenance and care of your fifth wheel top plate will assure you that you’re getting the most out of your fifth wheel plate. But even with all the proper care, your fifth wheel top plate will eventually need to be replaced. At Wheelco, we stock only the brands we trust to get the job done successfully. If you’re looking for high quality and brand name,SAF-Holland is your desired fifth wheel top plate. With their new innovative ELI-te fifth wheel top plate technology, SAF-Holland is a cut above the rest.

SAF-Holland

SAF-Holland has been around for nearly 100 years, specializing in coupling, lifting, and suspension systems for trucks, buses, tractors, and trailers. As a global supplier in the commercial transportation industry, SAF-Holland continues to provide new innovative technology such as ELI-te, the Electronic Locking Indicator Fifth Wheel Top Plate. This advanced top plate helps drivers GET IT RIGHT when coupling a trailer.

SAF-Holland’s ELI-te Top Plate extends road safety with the addition of red and white flashing LED lights, letting drivers know if they have successfully hooked-up to the trailer. Red LED warning lights will flash outward, warning the driver of a failed coupling. If a coupling is successful, high intensity white LED inspection lamps will light up the fifth wheel throat, making lock inspection easier and more reliable.

Next Step

There are plenty of options available for fifth wheel top plates and we know it can be a tough decision. Visit with our Wheelco team of aftermarket experts and service techs to help find the best fifth wheel plate for your needs. Give us a call or stop in to one of our store locations today.