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Generally speaking, air brake systems have larger brakes than hydralic systems. Some of the Type D heavy buses had 11" front brakes and 14" rear brakes.
If you keep the moisture out of your air brakes you generally have few problems with them. Hydralic oil can attract water and reduce the boiling point significantly, enough to create a real hazard on a long downhill. The only way to get moisture out of hydralic brakes is to flush the fluid.
Air brakes can be drained with petcocks on the tanks, air dryers, or moisture ejectors on a daily basis or as you drive. Moisture should never be a problem.
The parking brake on most hydralic systems is a band around the driveline. The don't always hold very well.
The parking brake on most air brake systems utilize the rear brakes and are applied by a spring under several hundreds of pounds of pressure. If your brakes are adjusted properly the bus is not going to move.
Since air brakes are a state requirement on all school buses over a certain size in WA State, you really don't have much choice in the matter around here. Particularly in the used market.
Would I purchase a bus with hydralic brakes? Yes, of course. Hydralic brakes are safe and can be used for years with few problems.
If two identical buses were for sale and one had air brakes and the other hydralic, would I prefer the air brakes? Of course. The parking brake alone is worth it. But only if the prices were similar.
Good luck.
Mark O. |
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