Large truck brakes

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  #1  
Old 05-05-09, 09:11 AM
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Large truck brakes

Do large trucks (semi's) have disk or drum brakes?
If air assist fails can the truck be stopped by mechanical means.
Or
Does the air release the brakes and upon failure of the air, the brakes come on and stay on
 

Last edited by frankiee; 05-05-09 at 09:12 AM. Reason: title clarification
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  #2  
Old 05-05-09, 10:08 AM
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1. drum brakes
2. If air is lost , Brakes apply

Good luck and have a great day
 
  #3  
Old 05-05-09, 05:21 PM
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Air brakes need the air applied to keep the brakes closed and away from the drums. If you lose air, the brakes apply themselves via spring action. You don't have to worry about stopping if you lose air. Hopefully it is a small leak and the brakes engage slowly. A massive loss of air.....hold on for the ride. You will stop, but without control.
 
  #4  
Old 05-05-09, 05:47 PM
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90% of North America trucks are air drum brakes however there are few have air disc brakes.


In European area it 50/50 split between disc and drum air brakes.

As far for Air brakes failures if the air supply do go out below 50~60 PSIG the parking brakes automatic apply no matter what. { if you going on the highway speed and suddenly you lost the air supply the parking brakes will come on really hard and what we called them " dyamiteing brakes " in exterme contions the trailer axles will actally come off from the trailer { it did happened once a while however I did broke the 5 Th wheel when it dyamiting on me }

some truck and I know pretty good percentage coach bus do have specal override for one time shot useage it will hold engough air to unlock the parking brakes { only if the air line is not cutted off } and move it to safe spot and done with it.

99% of North America CDL will required a airbrake test when you do get new commercal driver liscense.

The other thing about air brakes you will not feel the fade or wear on them so that one thing you will have to check from time to time to make sure your brake chamber rods do not overtravel if that happend you just loose that brake no question asked.

The other thing about air brake responds it will be about half to full second slower than hydrallic brakes but once it apply full force both are about the same.

Merci,Marc
 
  #5  
Old 05-05-09, 06:08 PM
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Yeah, the third air tank is nice. It holds just enough air to keep you from totally locking down on the expressway at 5pm. You can move the truck.
 
  #6  
Old 05-05-09, 06:12 PM
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That one thing I am very famuir with air brakes due I have two service trucks with airbrakes on them.

They are pretty easy to use it once you get used with it however just one major glitch is the tempture if you are in frezzing zone or colder you will need to add air brake antifrezze or rubbing achool in the system to keep the moisture out of the system.

Merci,Marc
 
  #7  
Old 05-06-09, 12:45 PM
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wow! in 30+ yrs. of driving both semi trucks and class a motor coaches, I've never seen or heard of dyamiteing brakes, I would love to learn more about this condition.As the freight that I haul is of a very unique type and any unfortunate accident could be devastating.

Frame failure before tire slide? interesting
 
  #8  
Old 05-06-09, 08:13 PM
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Originally Posted by liljman View Post
.

Frame failure before tire slide? interesting
Yeah with 750 HP on hand with whole unit grossed out at 90,714 KG { 200,000 lbs } that will do it.

My road tractor have triple driver while trailer is quad axle format so you can see why I did have very high gross weight there { yeah I have overweight and over size permit the same time }

But heard some spider wheels { spokes } they actally cut the valve stem off after dyamited now that will really raise fun factor to replace X numbers of tires what got damaged.

Merci,Marc
 
  #9  
Old 05-07-09, 07:35 AM
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That is interesting. But why would the spring brake, being an 1800 lb pressure cause more damage of that type in a "dynamiting" scenario than the service brake which can apply much more pressure to the brake?

With 70 lbs of applied air pressure you would be well over 2000 lbs of application pressure - depending on the size of the service pancake.
 
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