Skid Control, Jackknifing, and Emergency Procedures
Skids and jackknifes
A jackknife occurs when the trailer pushes the tractor sideways, folding the combination at the coupling. It is most often caused by overbraking the tractor (especially the drive wheels) or by driving too fast on a slippery surface. A trailer jackknife is when the trailer swings out; a tractor jackknife is when the tractor's drive wheels lock and the rear of the tractor slides.
Recovery
If the drive wheels lock and the tractor begins to jackknife, release the brakes to let the wheels roll and regain traction, then steer in the direction you want to go. If the trailer swings, steer into the skid - turn the wheel in the direction the trailer is moving - and avoid hard braking.
Emergency procedures
- Tire blowout: hold the wheel firmly, ease off the accelerator, and do not brake hard until you have control.
- Brake failure: downshift, use engine braking, and apply the parking brake gradually.
- Trailer breakaway: the emergency glad hand should automatically apply the trailer spring brakes.
Traps
- Questions ask whether to brake hard in a skid. No - release and steer.
- Another trap: steering away from the skid. Always steer into it.
- ABS questions: with ABS, keep firm pressure; without ABS, pump gently.
Rule of thumb
Release, steer into the skid, and do not overcorrect.