How To Adjust A Jost Fifth Wheel

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You have a Jost fifth-wheel plate in your truck, but it needs to be adjusted. How do you adjust a Jost fifth wheel?

Adjusting a Jost fifth wheel begins by loosening the jam nut and turning the adjustment screw one full rotation counter-clockwise to tighten the locking mechanism of the fifth wheel plate. If more tightening is needed, repeat the turning of the lock screw until the proper tension is reached.

Every day, hundreds of thousands of independent truckers hitch up their trailers to their semi trucks and move the goods Americans depend on. But as any semi-truck driver will tell you, having a secure and tight connection between the trailer and the truck is essential. With over 100,000 accidents involving semis occurring yearly, the key to protecting everyone on the road is ensuring the trailer stays right where it should (behind your truck). Since Jost is the industry leader in commercial fifth-wheel hitches, we wanted to help semi-truck owners learn how to adjust them when needed. If you feel some sway or jerking, or it has been a while since the last adjustment, chances are the hitch might need to be checked. How do you adjust a Jost fifth-wheel hitch? Well, we have the answer for you. So, keep reading.

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How To Adjust A Jost Fifth-Wheel Hitch

The Jost fifth-wheel hitch has four moving parts. The moving parts include the release handle, the release arm, the lockjaw, and a lock bar. The handle is pulled out when the fifth wheel plate is unlocked and pressed inward when the lock is in place.

The adjustment screw is located on the right side of the unit (just below the centerline). The screw tightens the lock bar, which is tapered, and moves the locking jaw tighter or looser as needed. As you adjust the screw, the locking jaw moves closer (the hole gets smaller).

The adjustment screw will rest against the lock bar, keeping it in the proper position. The purpose is to keep the locking jaws firmly around the kingpin when engaged. Turning the adjustment screw counter-clockwise will tighten the lock bar, while turning it clockwise will loosen the hold.

The Jost fifth wheel should come with a Jost lock tester. Move the lock tester into position, and hook the J-bolt under the fifth wheel plate's front edge (top). Once hooked, pull the handle on the lock tester up (toward the top of the faceplate) until the kingpin connects and is secure with the locking jaws of the fifth wheel hitch. Once locked, move the tester back and forth. If there is movement, you will need to continue to turn the adjustment screw until there is no movement by the lock tester component.

Unhook the J-hook from the top of the fifth wheel and move the lock tester from side to side. The tester should move sideways back and forth without moving forward or back. (Be careful to ensure that the top of the lock tester does not show any gap between it and the face plate).

If further adjustment is needed, loosen the jam nut and turn the central adjustment screw a complete turn counter-clockwise. (Remember to turn the adjustment screw counter-clockwise since turning it opposite loosens the connection and can result in a bent release arm). Retighten the jam nut and retest with the lock tester. Once the adjustment is correct, proceed with your trailer hookup.

For a helpful video on the adjustment procedure, see the YouTube Video.

What If More Adjustments Are Needed?

The adjustment screw for a Jost fifth-wheel hitch is located on the side of the mounting plate. Loosen the jam nut and turn the adjustment screw counter-clockwise. Then retighten the jam to hold the adjustment in place. (The process may have to be repeated until the proper adjustment has been reached).

What Are The Signs That the Fifth Wheel Plate Needs Adjusting?

Typically, fifth-wheel hitches don’t need adjusting that often. However, if you notice too much play or trailer sway, you might need to adjust the plate. A prime example of trailer sway is if your trailer fishtails while you are towing around a corner or if you feel a lot of jerking happening as you take off from a starting position. (We have all seen videos of tractor-trailers fishtailing back and forth while towing, rolling over, or worse, killing someone, so it is essential not to be that guy).

How Often Does A Fifth Wheel Hitch Need Adjusting?

While most semi-trailer hitches do not need to be adjusted often, the stress of everyday work can create issues. A fifth-wheel hitch should be inspected at least once a month or every 6 - 8K miles, whichever comes first.

Where Are Jost Hitches Made?

Jost International has grown into the leading purveyor of commercial fifth-wheel hitches for the trucking industry. The company patented the very first steel cast fifth wheel coupling mechanism (which has been duplicated across the industry). The company is headquartered in Grand Haven, MI, with another manufacturing plant located in Greeneville, Tn. The company offers various hitches for Semi-truck applications ranging from 6 tons to over 20 tons.

What Are Some Primary Causes Of Semi-Truck Accidents?

According to the Department of Transportation statistics, over 439,206 police-reported accidents involving large trucks occurred in 2020. (The last year where statistics are available). While many of these accidents resulted in a serious loss of property and damage, almost 5k people lost their lives, and over 146k people were injured (68% were occupants in other vehicles). There is no question that large semi-trucks are frequent travelers up and down American highways, and due to their prevalence, it is paramount to ensure that all equipment is functioning correctly before setting out on the road. While the numbers have been trending in the right direction over the past few years, it is crucial for every semi-trailer operator to be vigilant about the effects a bad connection could have to cause an accident.

Do Semis Cause A Lot Of Traffic Accidents?

While the majority of auto accidents that occur yearly do not involve Semi-trucks, about 2 - 3% of accidents result from a crash involving a big rig.

What is the Primary Cause Of Semi-Truck Accidents?

Fatigue tends to be the primary reason for accidents involving a tractor-trailer. Often, drivers push themselves to drive when they shouldn’t (they get paid for the loads they deliver and the miles they drive). Most states have laws about the length of time a driver can be behind the wheel, but despite the best efforts of law enforcement, drivers continue to push the boundaries of their limits.