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BURNING BUSES
As another bus burns do you believe there could be an inherent problem in the engine area and rear brakes in all prevost? My rear brakes locked up on one rear wheel but was caught in time !
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12 Replies
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No, I don’t think so. Prevost makes coaches that are very safe. I bet you can trace every fire back to user error (running on flat tires), lack of maintenance, or optional equipment that either failed, or was installed incorrectly.
You don’t see seated coaches burned up along side the road like you do conversions or entertainer coaches.
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Dan, I know on my bus fire it was 100% a shitty compressor replacement by a Carrier shop that eliminated the unloader valves because the mechanics were much smarter than the Prevost engineers.
NOT!
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On most, if not all? of our buses, the drive and tag axles have: 1) the normal “air/service” brakes; and 2) “spring” brakes that serve as parking and/or emergency brakes. If there’s a castastropic air system failure, the springs apply the brakes when air pressure drops below 60 psi.
On my bus when the key is ON and the pressure <60 psi there are multiple idiot lights that come on and a horn that sounds. Your results may vary?
Tag axle disc calipers, if they’re over greased or greased improperly, can cause the caliper to not release and possibly burn up the brakes, and possibly cause a fire.
Drive axle drum brakes if over greased the grease can end up on the linings and the drums and then the brakes aren’t as effective. If the linings and/or drums become too worn, the S-cam can go over center and not release and burn up the brake, and possibly cause a fire.Of course improperly lubricated bearing(s), or improperly torqued(end play) bearing(s) can cause heat and a fire.
Proper maintenance practices will prevent these problems. -
Proper maintenance practices will prevent these problems.That might be the problem.
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Fires caused by brakes are often operator error. Driver lets unit get Away on a downhill and keeps the brake pedal to the metal. Truckers do that and the trailer brakes burn the trailer. Electrical fires in many rv’s are common.
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We’re talking about dragging brakes, more often due to overgreasing the fitting, but also due to one not fully releasing when the parking brake is disengaged.
Poor driving habits are a whole other subject.
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If I have not used the coach in several months, on the first time out I stop after 20 miles and check the temperatures of the hubs/wheels. Just touching them is sufficient. If one is significantly hotter than the rest I investigate. This is how I caught a locked tag axle disc brake (my fault due to over greasing).
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Tirepressure monitor shouldcatch over temp also.
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Regarding over greasing the tag caliper and drum fitting… what is the proper procedure? This is on my long list for upcoming maintenance.
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Threegreens:
How did you overcome the over greasing after the fact?
Chuck
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John L, If you are doing the lube the shaft from the slack adjuster to the caliper has two fittings. All the grease does is lube the shaft so it rotates easily. One shot is all each fitting needs. With fittings such as tie rod ends, only apply enough grease to detect a slight motion on the rubber dust boots. The grease fitting is located so a relatively small amount of grease is all it takes to lube between the moving surfaces.
If you pay someone to lube your coach expect a ration of attitude because it seems they feel the more grease they pump the better the job.
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I just got done cleaning, inspecting, and adjusting all 6 brakes on my bus. On the drive axle, I pulled the axles out, removed the drums, hubs, and replaced the inner hub seals. Passenger side was starting to leak. I cleaned and painted everything. On the tag and steer axles, I inspected the pads, removed the slide pins, cleaned them, lubed them and their bushings. While I had the wheels off, I cleaned the inside of each.
To lube the disc brake calipers properly, they must be unadjusted, greased, then readjusted. Just pumping grease into the calipers can BURN things up.
Over greasing the drum brakes risks getting grease on your brake shoes(not good)
Below are the Meritor mx manuals links that describe the proper way to lube the drum and disc brakes, how to check then adjust the slack adjusters so the brakes work properly.Meritor cam drum brake mx manual mm4:
http://graphicvillage.org/meritor/mm4.pdf
Meritor Air disc brake mx manual mm4m:
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