How To Prevent A Jackknife

A jackknife occurs when the angle between the tractor and the trailer gets to a point where it can’t be straightened out by the driver. When action is taken promptly, an angle of up to 15 degrees is correctible.

Causes:

A jackknife can start with the trailer swinging out of line with the tractor, or it can originate with the tractor skidding sideways, Tractor skid out can occur when the drive wheels spin from too much power, or lock from over braking and from engine deceleration. Or it can be due to going into a turn too fast when the drive wheel tires can’t hold the tractor on course. That also can happen on a dry road. Too fast for conditions is usually the cause.
Trailer swing out usually results from over braking the trailer. Crowned roads, sharp turns, or rough roads can contribute to the problem as well.

Prevention:

The best way to prevent a jackknife is to prevent it from happening in the first place.
Here are some actions that will help prevent a jackknife.
* Brake before a turn, not in it.
* Apply power to the drive axle smoothly.
* Make smooth gear shifts and clutch engagements.
* Decelerate slowly, going easy on the brakes.

Trailer hand valves (trolley valves) have their place, but it’s easy to lock trailer wheels with them and that can start trailer swing. Keep an eye on the mirrors when making stops on ice. If the trailer starts getting out of line, release the brakes and get things straight before applying them again.

Steering is more important than braking when making a recovery. When the correction is started promptly, there is a pretty good chance of getting things lined up again. When the jackknife reaches 15 degrees, the chances diminish rapidly. If the trouble starts with the tractor skidding sideways, the trailer will quickly push it around to the point where damage may be done. The whole business happens in a matter of seconds. Either you make the right correction in that time or it’s too late.

Skillful drivers think ahead. They may leave room ahead to maneuver if jackknifing starts. They plan what to do if the tractor skids right or left. By planning ahead, by making sort of a "dry run" in their minds, they know what to do to keep control. They stay calm. They know a sudden jerk of the wheel makes things worse. When the tractor has a tendency to skid out, they back off the power. If they have to shift, they do it carefully. It’s easy to spin out right after shifting.

There are plenty of commercial truck drivers who have driven years without a jackknife. Superior performance doesn’t just happen. Thought, planning, and alertness are the ingredients of fine driving records.