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Heavy Duty Representatives Association (HDRA)

An association of independent heavy-duty manufacturers representatives.

Heavy-duty Coil Spring

Coil sprints having larger wire diameter, and 3 to 5 percent greater load-carrying capability than a conventional spring.

Heavy-duty Shock Absorber

Shock absorbers having improved seals, a single tube to reduce heat, and a rising rate valve for precise spring control.

Heavy-duty Truck

A truck having a gross vehicle weight of over 26,000 pounds (kilograms).

Heavy-duty Vehicle

Any motor vehicle having a gross vehicle-weight rating over 8,500 pounds (3,856 kilograms), that has a vehicle curb weight over 6,ooo pounds (2,722 kilograms), or has a frontal area exceeding 45 square feet (4.2 square meters).

HEC

1. Acronym for Hybrid Instrument Cluster and Module (Ford).

Hecto

The prefix representing the number 100.

HEDF

High electro-drive fan.

Heel

1. The innermost part of the gear tooth on a ring and pinion gear set. 2. The bottommost portion of a cam on a camshaft.

Heel And Toe

The act of applying one's right toes to the brake pedal while applying the right heel to the accelerator to slow the vehicle as it enters a turn while keeping the engine revved up.

Heel To Toe Clearance

The space between the brake drum and the heel and toe of a brake shoe.

Heel-and-toe

A racing or high-performance driving technique in which the driver uses the right foot to operate the brake and gas pedal simultaneously, using the toe on the throttle and the heel on the brake. This leaves the left foot to work the clutch. The heel-and-toe technique is often used to match the engine speed to the rate at which the transmission will be turning when the driver downshifts.

HEGO

An acronym for heated exhaust gas-oxygen sensor.

HEGOG

Heated exhaust gas oxygen-ground.

HEI

An acronym for the General Motors high-energy ignition system.

Height Sensor

A sensor used to monitor the corner heigh of a vehicle for the level control system.

Height-sensing Proportioning Valve

A proportioning valve in which hydraulic pressure is adjusted automatically according to the vertical movement of the chassis in relation to the rear axle during braking; sometimes also called a weight-sensing proportioning valve.

Heim Joint

A spherical-rod end joint that allows precise adjustment of wheel position.

Heli-Coil

A trade name for a screw-thread insert used to repair damaged internal threads.

Heliarc

The trade name of a tungsten inert-gas form of welding developed by Linde Welding and Cutting Systems.