Technical information

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Technician Guidelines for Antilock Braking Systems

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Power Jackknife A non-braking induced condition whereby the drive wheels of a

tractor will spin under engine power, resulting in a loss of

lateral stability.

Quick-Release Valve A commonly used valve located close to a brake chamber that

decreases the time required to exhaust air pressure from it.

Reference Speed An ideal rate of wheel speed deceleration (optimum wheel slip)

calculated by the ECU and based on actual wheel speed infor-

mation at the moment that the ABS is activated. The ECU

compares actual wheel speed to the reference wheel speed

during an ABS event and adjusts the brake application pressure

in an attempt to match the actual wheel speed with the ideal

reference speed.

Relay Valve See ABS Relay Valve for definition as it pertains to ABSs.

Retarder Control A system which prevents the tractor drive axle(s) from locking

on slippery surfaces by disabling the engine retarder during an

ABS event.

RFI Radio frequency interference. A type of electromagnetic inter-

ference (EMI) that occurs only in the radio frequency band. See

Electromagnetic Interference.

SAE Society of Automotive Engineers. An organization that sets

voluntary engineering standards for automotive and aerospace

components, systems, and vehicles. See J560, J1587 and

J1708.

Select High A system design in which ABS bases all control decisions to

release or apply brakes to an axle or tandem on the highest

measured wheel speed. Under this design, ABS won’t start

cycling until all sensed wheels experience a tendency to lock.

Select Low A system design in which the ABS bases all control decisions to

release or apply brakes to an axle or tandem on the lowest

measured wheel speed. If only one wheel locks, the ABS on all

other controlled wheels on that axle or tandem will also cycle.

Sensor Bushing The friction spring device that is first inserted into the sensor

block, allowing the sensor pickup to be adjusted and holding it

in position during vehicle operation. Also called a spring clip.