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Key Takeaways

  • Master each process of adjusting a Jost fifth wheel for seamless trailer connections.
  • Ensure secure and safe towing by properly positioning and tightening the bolts.
  • Gain confidence in your hitching skills and eliminate frustrating coupling issues.

Tired of uncertain trailer coupling? Follow our guide to adjusting a Jost fifth wheel like a pro. Enjoy smooth hitching and worry-free towing experiences!

To adjust a Jost fifth wheel, park on level ground, loosen the adjustment bolts, move the fifth wheel to the desired position, tighten the bolts, test the coupling with a tug, and repeat if necessary. Ensure safe and smooth towing.

As a seasoned expert in the field, I've delved deep into this topic, gathering insights from industry professionals and conducting extensive hands-on research. So, rest assured, I understand the frustration that comes with hitching issues. I’ll share my firsthand experience and expert opinions, empowering you to conquer the art of adjusting a Jost fifth wheel like a pro.



How to Adjust a Jost Fifth Wheel

When it comes to maintaining the safety and efficiency of your truck's fifth-wheel coupling system, knowing how to adjust a Jost fifth wheel is essential. As a crucial connection point between the truck and trailer, the fifth wheel significantly ensures a secure and stable link during transportation.

However, these components may experience wear and tear over time, necessitating adjustments to guarantee optimal performance.

The process of adjusting a Jost fifth wheel involves manipulating the lock adjustment screw, which directly affects the positioning of the lock bar within the fifth wheel assembly.

Adjusting the Jost Fifth Wheel

To maintain optimal performance and safety, it's crucial to ensure that your Jost fifth wheel is adjusted correctly.

Follow these steps from the official JOST International website:

  1. Locate the lock adjustment screw: It is located on the left-hand side of the fifth wheel.
  2. Loosen the locknut: Using your 24mm tools, loosen the locknut on the adjustment screw.
  3. Wind the adjustment screw outwards until it becomes loose.
  4. Check the lock bar: Observe the lock bar's movement when you insert the lock tester in the fifth wheel. The lock bar should be tight around the kingpin and rotate freely with the lock tester.
  5. Adjust as needed:
  • If the lock bar is too tight, loosen the adjustment screw clockwise.
  • If the lock bar is too loose, turn the adjustment screw counterclockwise to tighten it.
  1. Secure the adjustment: Once the lock bar is adjusted correctly, tighten the locknut against the housing.
  2. Perform a final check: Lock and unlock the fifth wheel several times and use the lock tester to ensure proper operation.

Remember to inspect the release handle, release arm, and other connections related to the fifth wheel before and after adjustment, as mentioned in this tutorial.

Understanding Jost Fifth Wheel


The main components of a Jost fifth wheel include the lock bar, release arm, release handle, and adjustment screw.

  • Lock Bar: The lock bar securely holds the kingpin when the trailer is connected to the truck.
  • Release Arm: This component allows you to release the lock bar and detach the trailer from the truck.
  • Release Handle: The handle is used to activate the release arm.
  • Adjustment Screw: This screw is used to make adjustments to the lock bar, ensuring that it holds the kingpin tightly.


The main function of the Jost fifth wheel is to provide a secure connection between your truck and trailer. When adjusted correctly, the lock bar holds the kingpin in place, preventing any unwanted movement and ensuring a safe connection between both vehicles.

To adjust a Jost fifth wheel, you will need to:

  1. Locate the lock adjustment screw on the left-hand side of the fifth wheel.
  2. Loosen the locknut on the adjustment screw using a 24mm ring spanner or socket.
  3. Wind the adjustment screw outwards until it becomes loose.
  4. Use a measuring tool to check the clearance between the lock bar and the kingpin. The recommended clearance is 2mm to 4mm.
  5. Tighten the locknut to secure the adjustment screw in place.

Handy Tips for Adjusting Your Jost Fifth Wheel

To avoid any issues with your truck and trailer connection, follow these handy tips when adjusting your Jost fifth wheel:

Keep it Clean

Regularly clean the fifth wheel components and grease the lock bar, adjust the screw, and release the arm. This will help to prevent excessive wear and tear and keep your fifth wheel functioning optimally.

Regular Inspections

Inspect your fifth wheel every 6 months or 15,000 miles, depending on your truck's usage. This will help to identify any issues early and ensure your fifth wheel operates safely and efficiently.

Seek Professional Help

If you're unsure about adjusting your Jost fifth wheel, consult a trained technician. They can help ensure everything functions as it should and make any necessary adjustments on your behalf.

For further information and support, be sure to check the Jost International website, where you can find helpful resources, including maintenance procedures and product manuals.

Preparation for Adjustment

Before adjusting a JOST fifth wheel, it is crucial to prepare accordingly to ensure safety and efficiency during the process.

Safety Precautions

Always observe proper safety precautions when working on a fifth wheel. It is essential to:

  • Ensure the truck is parked on a level surface, with the engine turned off and a parking brake applied.
  • Disconnect the trailer to prevent accidental movement.
  • Wear protective gloves and safety goggles to avoid injuries.
  • Keep a fire extinguisher nearby in case of emergencies.
  • Check for signs of damage or wear on the fifth wheel and related components as these may hinder proper functionality or pose safety risks.

Gathering Tools

Gather the appropriate tools for the job, which include:

  • Two 24mm ring spanners or a 24mm ring spanner and a 24mm socket.
  • A lock tester for checking the adjustment.
  • A torque wrench to tighten the locknuts.

Common Adjustment Issues

It is essential to be aware of potential issues that may develop during the adjustment process.

Some common problems include:

  • Worn or damaged components causing adjustment difficulties: Replace these before continuing.
  • The release arm or handle may not engage properly, indicating an issue with their connection or a damaged spring.
  • Excessive movement in the fifth wheel once connected to the trailer may indicate the need for further adjustment.

Inspecting the Fifth Wheel

Checking for Wear

When it comes to maintaining your truck, inspecting the fifth wheel is a crucial step to ensure your vehicle performs efficiently. One of the key aspects of fifth wheel inspection is checking for wear.

Look for signs of wear on various components, including the lock bar, release arm, and release handle. If any of these parts appear worn, replacing them with genuine parts is crucial. Replacing worn components ensures that your fifth wheel will function optimally and remain safely connected to your trailer.

JOST International provides a helpful maintenance guide for JSK 37U Fifth Wheels.

When inspecting your fifth wheel, it's essential to go through a list of key components and features.

Some areas to focus on include:

  • Bracket pin bolts and locking tabs
  • Bent or broken parts
  • Corrosion or rust
  • Performance during the winter season

Identifying Issues

During the inspection process, watch for specific issues such as loose or improperly adjusted components. You'll need to locate the adjustment screw on the left-hand side of the fifth wheel and use a 24mm ring spanner or socket to loosen the locknut.

A loose adjustment screw can lead to reduced performance and safety concerns. If you identify a loose or improperly adjusted lock bar, it's important to follow the appropriate steps to make adjustments. Rotating the screw outwards until it is loose will help ensure that the lock bar is adjusted correctly.

You can find specific adjustment guidelines in your truck’s owner’s manual or on the official JOST website. Other measures to ensure optimal performance include routinely greasing the components and cleaning the top plate.

Key Component Inspection Tips
Bracket pin bolts Ensure locking tabs are properly secured
Lock bar Check for wear and proper adjustment
Release arm Inspect for signs of wear or damage
Release handle Ensure it’s functioning smoothly

Adjustment Process

Releasing the Lock

Begin by locating the release arm or release handle connected to the fifth wheel. Lift the release arm upward or pull the release handle back to disengage the lock bar.

Adjusting the Kingpin

Next, focus on the adjustment screw, which is critical to the process. You will find the lock adjustment screw on the left-hand side of the fifth wheel. To begin adjusting the kingpin, two 24mm ring spanners, a 24mm ring spanner, and a 24mm socket are required.

Tool Size
Ring Spanner 24mm
Socket 24mm

Before adjusting, loosen the locknut on the adjustment screw. Rotate the adjustment screw outwards until it becomes loose. To ensure proper kingpin adjustment, measure the gap between the kingpin and the lock bar when connected to a trailer.

Tightening the Lock

Once the kingpin is properly adjusted, focus on tightening the fifth wheel's lock. Rotate the adjustment screw inward to tighten the lock bar. Using a lock tester or other suitable tool, check the fifth wheel's lock bar several times for proper engagement.

A lock bar is adjusted correctly when it:

  • Locks and unlocks each time easily
  • The lock tester rotates smoothly and securely

With the lock bar tightened, secure the locknut to prevent unwanted movement. Regularly inspect the fifth wheel and all its components for signs of wear or damage. A worn or damaged fifth wheel can lead to unsafe conditions when towing a trailer with your truck.

Maintenance Tips

Maintaining your Jost fifth wheel is essential for optimal performance, safety, and longevity.


Proper lubrication is essential for the smooth operation of the fifth wheel. It reduces wear and tear on all moving parts and ensures that the lock bar, release arm, and release handle function smoothly.

To lubricate your Jost fifth wheel:

  1. Disconnect the trailer from the truck to ensure easy access.
  2. Clean off any old grease and debris from the fifth wheel's surface.
  3. Apply the lubricant to all-wheel moving parts, including the lock bar, release arm, and release handle.
  4. Reconnect the trailer and ensure proper functionality of the fifth wheel.

Regular Inspection

Regular inspections should include checking for:

  • Excessive wear on the lock bar and lockjaw
  • Proper adjustment of the adjustment screw
  • Signs of damage or wear on the release arm and release handle
  • Proper alignment and smooth operation of the wheel