To be operated properly, the haul truck should back up to the spreader; a coupling on the spreader should engage on the rear of the truck; the coupling should lock securely together; and the spreader box should pull the truck (in neutral gear position) behind it. The truck should not push the spreader box. This is very important, because the amount of aggregate covering the asphalt depends partially on the traveling speed of the spreader. Thus, to maintain a constant speed and ensure a uniform aggregate application rate, the spreader must regulate its own speed.

The spreader coupling must be able to lock securely with the truck hitch, and the spreader box operator must be able to release the hitch easily and quickly. Figure 7‑28 is a photo of a typical spreader box truck hitch arrangement.

The truck hitch should be visually checked for anything broken or bent. Ensure the locking mechanism is working properly by having a truck hook up to the spreader box. Have the operator manipulate the release to be sure it will disengage the truck effectively.