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Time for a new bus. billowing smoke until I warm up to operating temp. on my ford 6.6...i can see tickets in my near future. the only thing i can't decide is air or hydraulic brakes. i know from experience that hydaulic parts are expensive and the pedal pressure is uncomforatably high. but do air brakes have the "feel" that hydraulics have on, say, slippery surfaces?? i've seen air cylinders around $30 (rebuilt) which is reasonable and i got to look at the internels of a air brake front end and it seems more stout overall. comments?
There are advantages to air brakes - it also depends where you live and how large the bus is. Living in the mountains, air brakes are preferable. They have a good feel to them when using them. Here's one consideration; if a hydraulic line fails, you lose braking power. If an air line goes, the wheel will brake. Air pressure is used to disengage the brake, so when there is no air the brakes engage.
You may want to read up on air brakes through the DOT - Good luck with it.
Something else to consider: Brake pressure applied on hydrualic brakes is proportional to how hard you push the pedal. With air brakes, it's how *FAR* you push the pedal; pedal pressure is usually 20 to 25 pounds of force from the top to the floor. It's a different mindset.
First time I drove a vehicle with air brakes, I was very proud of myself: for not putting myself through the windshield!
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.
I just bought a 1990 Prevost Le Mirage XL.
I am in Heaven. Except when I have to back it up! The brakes work great when going forward. When I back up the brakes growl, shudder and grab. What might be causing this? Anybody? Thanks, Bob
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