[Vwdiesel] Air Brakes

[Kurt Nolte]

That would make a lot of sense, then. If the buses were '96 vintage and 
you were seeing them 7-10 years later, they were nearing the end of 
their expected service life anyway.

The buses we run have an expected service life of 12 years, when all the 
regularly scheduled maintenance, PM, and necessary repairs are done in a 
timely manner. Letting that slip, even slightly, can result in some 
fairly severe losses in service life. Add to that the fact that service 
lives are longer now than they were in the 90s, and it's very possible, 
even likely, that the buses you were dealing with were near, or even 
beyond, their service lifetime.

-Kurt


Dave Cook wrote:
> Hmm, I drove from Fall '03 to Summer '06.  The two air-brake busses they had were build, I think, '96ish.  
>
> Those two busses were comfy, but worn out.  The air conditioners almost never worked, they leaked oil like a seive, on and on and on.  The older of the two burned up a year or so after I quit.  I can't remember for sure the problem, but I think they traced it to a bearing in the engine (like alternator or something) that got too hot and eventually setting the engine alight.
>
> Luckily, everyone was able to get off and all were safe.  Though, when the insurance company started talking to the students, it seemed each one of them had lost a very nice iPod in the fire!    
>
> But what you say makes sense, thanks for the explanation.
>
> Dave Cook
>
>
> --- On Wed, 12/2/09, Kurt Nolte <syncronized_turbo at yahoo.co.uk> wrote:
>
>   
>> From: Kurt Nolte <syncronized_turbo at yahoo.co.uk>
>> Subject: Re: [Vwdiesel] Air Brakes
>> To: vwdiesel at vwfans.com
>> Date: Wednesday, December 2, 2009, 5:05 PM
>> Dave Cook wrote:
>>     
>>> I could never figure out why air brakes were better on
>>>       
>> the bigger busses than hydraulic.  Seemed like the
>> mechanics were always needing to dink with something in they
>> systems because the tank wouldn't work right, or there was a
>> problem with one of the cylinders, or something. 
>> Whereas on the regular busses, the only brake issues ever
>> were typical replacing pads/rotors occasionally.  
>>     
>>> I can see on a semi tractor/trailer where air brakes
>>>       
>> would be beneficial, IE being able to hook up the trailer,
>> and have brakes without the problem of bleeding hydraulic
>> brakes or something like that.  
>>     
>>> But why on a larger bus would they be better? 
>>>       
>> Just seems like more possibility of things to go wrong.
>>
>> One advantage is the inherent safety feature: something
>> goes wrong, the 
>> brakes engage, end of story.
>>
>> The other is the fact that the "working fluid" is
>> constantly being 
>> cycled out of the system, and the temperature of the fluid
>> makes no real 
>> difference. In a hydraulic system, you'll continually build
>> up heat in 
>> the brake fluid as you engage the brakes repeatedly.
>> Eventually you can 
>> build up enough heat to boil your fluid, then you're
>> screwed.. The 
>> heavier the vehicle, the faster you build up that critical
>> volume of heat.
>>
>> With an air brake vehicle, you're dumping that hot air out
>> of the brake 
>> lines each time you depress the pedal, replacing it with
>> cooler 
>> compressed air each time you release the pedal. You just
>> don't ever 
>> build up the kinds of critical heat levels that you can in
>> hydraulic 
>> systems, because you're cycling the working fluid out so
>> frequently.
>>
>> The bus company I work for has three hydraulic brake
>> "school bus" 
>> chassis vehicles, and their brakes are /horrible/ once you
>> get deep into 
>> a work shift. We use them for short trips and short shift
>> replacements 
>> because of that fact. School buses aren't meant to run
>> stop/go for 
>> 8-9-10-15 hours per day like a heavy transit bus, so they
>> can get away 
>> with having hydraulic brakes.
>>
>> Most school buses, at least in the local districts, are
>> air-brake 
>> vehicles now. South Carolina automatically tests you for
>> air brakes when 
>> you take your CDL tests, unless you specifically request
>> not to be. It's 
>> not an endorsement anymore, but you get a restriction if
>> you don't pass 
>> that part of the test.
>>
>> I'm not sure when you drove a school bus or how old the air
>> tech on the 
>> ones that constantly had to be messed with was, but ours
>> are pretty 
>> reliable. They do require more frequent servicing than a
>> hydraulic 
>> system might, but that service is pretty limited to just
>> draining 
>> accumulated water from the system and making sure the air
>> dryer is 
>> refreshed on schedule.
>>
>> -Kurt
>>
>>
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>>     
>
>
>       
>
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