What are the chances you know asphalt?

Rear rear brakes. The paver bumps the rear tires to control paving speed, so if the cans extend past the tires, the roller will contact the cans first. 

With two or more pushers, the cans grow to hold the loaded chassis on a 20% grade with all lift axles raised (FMVSS 121). 30/36 is common and is shown.

Check brake orientation. Some suspensions move the cans forward of the axle. Inverted cans may help. Mack has nice compact installation. Disc brakes solve the problem, since the cans are perpendicular to the spider. 

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