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Thread: Engine "Jake" Brake Use

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    Default Engine "Jake" Brake Use

    I have been a Lt for my dept for 5 years now and the other da while responding to a call in light rain, the capt shuddered when i used the jake brake while responding, and then he told me to turn it off. He misquoted the operators manual and then misquoted NFPA 1500 regarding the use of jake brake in rain. He then told me to check out ffclosecalls.com and nearmiss.com and i found very little on the subject. Can anybody give me any info (good or bad) in this subject. I would appreciate it. Also let me finish by giving some background, I have been drivin the vehicle since 2003 sine I starte working for this dept, proir to that I drove aparatus on a volunteer department that had apparatus like equipped since 1995 and also have driven over the road tractor trailers equiped with jake brakes for several years. Any onfo would be appreciated. Thanks

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    Like any other accessory on a vehicle, an auxiliary braking device (whether it be a Jacobs Brake, a Mack Powerleash, Blue Ox, an exhaust brake, a Telma driveline retarder, etc etc etc.....) is a tool designed to assist you accomplish your job. It's use certainly is not mandatory, but it sure does make life easier.

    That said, to use it, you should have a basic idea of the physics behind it. Every manual I have ever seen for any device (I have driven something with almost everything listed above in the United States Government's extensive fleet of fire apparatus) specifically states that the device should not be used when road conditions present slippery conditions. Some, like the Jacobs Brakes, also state not to use them in wet conditions, as the auxiliary brake system could potentially cause the wheels to lock up.

    Do I buy that wet roads will cause an activated Jake to lock the wheels? Granted I am an educated man, but I cannot speak eloquently on the physics of a Jake Brake, however I am awfully skeptical. But in the end, any apparatus operator worth half his weight uses due diligence in any hazardous road conditions in inclement weather; and acts appropriately- so turning off the device should have no bearing on the operation of the vehicle.

    In short: Operators manuals will tell you not to use the device in wet or snow/ice.

    I do not know if NFPA 1500 addresses the issue so I will not comment.
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    In SLIPPERY conditions, ANY kind of braking in excess of the traction your tires have at the time will cause the tires to start sliding. It would be no different than applying too much brake pressure in the rain or snow. It doesn't really matter what is applying a braking force the wheels, the effect is the same.

    A blanket statement of no jake brake use in rain is wrong. In heavy rain, I would consider using a lower setting. If the road is covered in snow or ice, I would use low or off depending on the conditions.

    As to whether a Jake or any other auxillary braking system will lock the wheels, no. Its not possible. Unless the system is magically locking the torque converter and stopping the crankshaft of the engine from turning with the transmission in gear, the wheels are not locking up. Whats happening is the lack of traction breaks the tires loose from the road. The tires will be spinning still, just not gripping the road while they're doing it.
    Last edited by nmfire; 03-22-2010 at 10:18 PM.
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    We have had our engine lockup before because of the exhaust brake. We never run it on wet roads and definatly not on icy or snow covered roads.

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    Quote Originally Posted by nmfire View Post

    As to whether a Jake or any other auxillary braking system will lock the wheels, no. Its not possible. Unless the system is magically locking the torque converter and stopping the crankshaft of the engine from turning with the transmission in gear, the wheels are not locking up. Whats happening is the lack of traction breaks the tires loose from the road. The tires will be spinning still, just not gripping the road while they're doing it.

    Then is it best to leave it off and let the anti-lock brakes prevent the wheels from locking up and the breaking traction from the road?

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    Quote Originally Posted by prnancoz View Post
    Then is it best to leave it off and let the anti-lock brakes prevent the wheels from locking up and the breaking traction from the road?
    NMfire's description is technically quite correct in that an auxiliary braking system will not "lock" the wheels. What does happen is a sudden change in the of the torque applied to the drive wheels. You go from light braking to an abrupt addition of braking forces, or from minimal torque (drifting), or from torque moving the vehicle forward to opposite torque. In the case of a wet, snow or ice covered road surface, the friction between the tires and the road surface is materially reduced. As NM states, when the road surface is unstable, if any of these changes in torque are sufficient to overcome the friction, a skid can occur. The more radical the change or the more sudden the change, the more likely it is to happen. While no actual wheel lockup takes place, the effect is quite the same.

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    I agree with the above statements about exhaust brakes and retarders causing sudden excess braking on slick roads.

    That said, I believe that apparatuses with ABS can be driven with aux. braking devices engaged.

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    I cannot speak from any one manufacturer of trucks but, in several of our owners manuals it states "it is recommended that the use of auxillary braking devices not be used in increment weather"

    In my opinion that is a recomendation to cover the manufacurers butt in the chance of an accident.
    I personally prefer to use them all the time but I also drive a truck for a living so I have a fair amount of miles under my belt.
    DKA 5816 likes this.

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    Quote Originally Posted by footrat View Post
    I agree with the above statements about exhaust brakes and retarders causing sudden excess braking on slick roads.

    That said, I believe that apparatuses with ABS can be driven with aux. braking devices engaged.
    I have to question that. ABS systems can control the application of the vehicle's service brakes. I do not believe that any auxiliary brake can react to the ABS control at the same rate as the service brakes. The one possible exception would be the Telma retarder.

    I believe that attempting to have ABS control other retarders would lead to very erractic braking, similar to pumping the brakes on an ABS equipped auto.

    Please note: This is only from my understanding of the physics involved, not from any actual occurrence. Our newest engine is equipped with a 3 stage jake and ABS. I normally run with the jake in the medium setting except on slick roads. I have not to this point gotten into a situation where the jake was on and the ABS actually operating.

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    I used to be very skeptical when people or manuals told me to turn off the Jake in wet conditions, then I had 50,000lbs of fire truck come unglued from the pavement in light rain, luckily I was operating well within my capabilities and I quickly recovered, but had anything gone wrong...

    I know a fair bit about how these systems work, and in modern trucks the ABS is tied into the jake controller so that should a skid start it will disengage the engine brake, however there is considerable delay compared to when it dumps the regular brakes.

    In my case the light rain was just enough to make the roads a little greasy, we were responding MA to a working fire. Following SOP I was coming to a complete stop at all red lights (we don't use preemption). The first light I felt a little squirrelly right after letting off the gas, I wondered "did I just skid?" The second light caught me a little short so I got off the gas and hit the brakes and boom (literally), rear end came around about half the width of the truck before the ABS kicked in. The combination of the Jake on high and just a little brake was all it took. Had there been a car to my right I would have hit it.

    I now turn off the Jake when responding in the rain, I do however leave it on low for routine driving as I am less likely to be pushing the limits of traction just heading around town.

    edit: Chief, if the ABS detects a skid it just disengages, it does not "pump" the engine brake. Once the skid condition is cleared it will allow the jake to turn back, I do not know if there is a "time out" before cycling or if its immediate, if so you could end up in a negative feedback cycle.
    Last edited by Fire304; 03-23-2010 at 08:49 PM.
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    I had a man tell me one time...... The gear you go up the hill should be the gear you go down in. He never drove a truck with an auxillary braking system that I can think of.
    Just a thought. We never use the jake while traveling on snow/ice covered roads, nor do we use it while operating on clear roads while the chains are still on. From November till March, the Chains are on.

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    Quote Originally Posted by Fire304 View Post

    edit: Chief, if the ABS detects a skid it just disengages, it does not "pump" the engine brake. Once the skid condition is cleared it will allow the jake to turn back, I do not know if there is a "time out" before cycling or if its immediate, if so you could end up in a negative feedback cycle.
    Thanks for the clarification. I will definitely go back and reread the info on it.

    farmerfire1156 "I had a man tell me one time...... The gear you go up the hill should be the gear you go down in. He never drove a truck with an auxillary braking system that I can think of."

    1156, none of my trucks ever had jakes, either. I learned the same rule, and for my money, it still applies, jake or no.

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    I just read through my Spartan and Caterpillar instruction manuals. They agree that the jake is disabled when the ABS is activated. They point out that if you are on an unstable road surface and have an ABS fault light the jake should be shut off as under that condition the ABS will not disable the jake.

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    Quote Originally Posted by chiefengineer11
    I just read through my Spartan and Caterpillar instruction manuals. They agree that the jake is disabled when the ABS is activated. They point out that if you are on an unstable road surface and have an ABS fault light the jake should be shut off as under that condition the ABS will not disable the jake.
    The same is true with those that have ABS and Telma retarders. When the ABS kicks on, the Telma is taken away. However, if there is an ABS fault, the Telma is turned off, and unusable.

    FM1
    Last edited by FIREMECH1; 03-25-2010 at 01:22 AM. Reason: more info....
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    One of the issues related to skidding with the Jake is that it only applies to the drive axle (the rear). Therefore going down a slippery road and suddenly just the rear axle "brakes" causes a chance to skid. This is magnified significantly if this occurs in a turn.

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    Quote Originally Posted by farmerfire1156 View Post
    Just a thought. We never use the jake while traveling on snow/ice covered roads, nor do we use it while operating on clear roads while the chains are still on. From November till March, the Chains are on.
    Why would you have chains on from November to March if you're Way South of the Mason Dixon Line? Are you afraid you'll get a half inch of snow. I hope you only run a few calls a year. Our city would go ballistic if we were tearing up the streets with chains when the roads are clear. We would have to have a heck of a lot of snow and ice before we would put on the chains. But we are used to driving in the snow.

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    Haven't "ironed" a rig in over ten years. Seldom shut the Jakes down either. Might set them to low but almost NEVER off. Ours shut down at about 1200RPM so usually they are OFF by the time you've slowed enough for you to stop. T.C.

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    Exclamation Summary

    A few people have touched on various issues, but overall, you're taking a risk when using them in rain (light or heavy) or snow. The Jake-brakes and Telma-retarders slow the rear wheels only when your foot comes off of the accelerator. If the road is slippery, this can cause the truck to skid.

    Might be a little over-dramatic, but think of applying only the rear brakes on the truck in 4" of snow. In a semi, this can cause the trailer to try and pass the cab (jack-knife). If a fire truck, provided it's not a tiller, the back end of the truck could slide towards the shoulder simply due to road-crowning, or another direction due to a curve.

    Light rain is risky because it adds just enough water to the road (that usually has at least a little bit of an oil film on it) to make it slick.

    Experience is going to play a big part in this. Those of us who have been driving for a long time may be able to use them in certain situations that others would not. But overall, it really is in ALL of our best interests to not use them any time the roads are questionable (even loose gravel and wet leaves could be a problem).

    Hope this helps.
    Last edited by Tim1118; 06-09-2010 at 04:01 PM.
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    Quote Originally Posted by Tim1118
    A few people have touched on various issues, but overall, you're taking a risk when using them in rain (light or heavy) or snow. The Jake-brakes and Telma-retarders slow the rear wheels only when your foot comes off of the accelerator. If the road is slippery, this can cause the truck to skid.
    Your info on the Telma retarders is WRONG!!! They are only activated by hand or foot controls. Telma's are controlled by the air pressure given either by a hand control, or off the air pressure of the foot treadle valve. They do not work off the accelerator, as jake or compression brakes do.

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    If I am wrong, I apologize...

    However, I have driven several fire apparatus equipped with Telma Retarders, and they all started to engage when I took my foot off of the accelerator pedal. In fact, in spec'ing a few apparatus, I've been able to specify to what stage it would engage to off of accelerator. Maybe you could shed some light on this?

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    Quote Originally Posted by Tim1118
    If I am wrong, I apologize...

    However, I have driven several fire apparatus equipped with Telma Retarders, and they all started to engage when I took my foot off of the accelerator pedal. In fact, in spec'ing a few apparatus, I've been able to specify to what stage it would engage to off of accelerator. Maybe you could shed some light on this?
    I'll apologize first.

    Found out that they do make an off-throttle system. Not sure when they came out with it, but they do make it.

    I stand corrected.

    FM1
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