How do Jake Brakes Work

Discussion in 'Shop Talk' started by Ken Scharabok, Jun 5, 2005.

  1. Ken Scharabok

    Ken Scharabok In Remembrance

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    Several communities in the area have a No Jake Brakes sign at the city limits. I understand Jake brakes are used to slow down a truck via the engine - and are loud. Just out of curiosity, how do they work and why are they noisy?
     
  2. fordy

    fordy Well-Known Member

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    ...................Basically , they have a round , flat plate that pivots inside the exhaust pipe . As this is swiveled to an ever increasing "closed position" the exhaust gas is prevented from being "pushed" out of the combustion chamber by the piston thereby creating an opposing force pushing Against the Piston\crankshaft which retards the forward movement of the Truck via the driveline . They are very noisey but efficient devices . fordy... :)
     

  3. Blu3duk

    Blu3duk Well-Known Member

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    They are called compression brakes..... "jake Brake" is the short name for the jacobs version of the compression brake and kinda the generic name that has stuck since the invention caught on outside the hills of logging areas and were puton OTR trucks in increasing numbers the past 30 years.

    Willim
     
  4. Darren

    Darren Still an :censored:

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    The original design Jacobs Brake works by controlling the exhaust valve so that instead of firing the mixture it's compressed and released. The compression slows the engine and the truck.The noise is the release of the compressed gas from the cylinders. Thus the rapid blat-blat-blat-blat-blat-blat-blat-blat-blat you hear when the brake is activated. Unlike the air brakes which only work as long as there's enough air pressure, the Jake Brake is a safety feature on a heavy truck that continues to work to prevent runaways.

    http://www.bernhardbus.com/theory.htm
     
  5. WanderingOak

    WanderingOak Well-Known Member

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    I have heard that the Jacobs Brake company is trying to prevent the term 'Jake Brake' from becoming generic for engine brakes. Supposedly, if you see a sign saying 'No Jake Brakes in town', you can contact the Jacobs Brake company, and they will contact the town to have them change the sign to 'Engine Brakes'. I beleive at one point in time there was a 'sign bounty', although I could be mistaken.
     
  6. Hip_Shot_Hanna

    Hip_Shot_Hanna Well-Known Member

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    a lot of the noise from a Jake Brake is from the exhaust gasses being spit back into the inlet manifold when the inlet valve opens , the gass has nowhere else to go as the exhaust valve fails to open
     
  7. nicholascovey

    nicholascovey Well-Known Member

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    Darren posted: "Unlike the air brakes which only work as long as there's enough air pressure"

    Uh, actually they only RELEASE when there's enough pressure. They are actually spring actuated so that they are in effect locked when there is no pressure. This was done for obvious safety reasons.

    Sorry, minor detail nit-pick; Carry on!
     
  8. Darren

    Darren Still an :censored:

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    You're correct. You have to have enough pressure to release the brakes before you can drive off. I should have added, that by the time the driver's hears the alarm, there's a good chance on a long steep downgrade that the brakes have overheated to the point that even the spring brakes won't stop the truck. You can often smell the hot brakes on trucks with drivers that don't know how to safely operate. The old mantra of descending in the same gear in which you ascended the hill doesn't always apply with the high horsepower engines of today.

    Unless a driver loses a driveshaft or something else compromises the drive train, there's no reason for the runaway truck ramps if the driver does in fact know what they're doing. I saw the result of a loaded tandem dump that lost its brakes on a long downhill. The spring brakes didn't prevent the out of control truck from tearing the front porch off a house and killing the woman who was sweeping the porch. A jake brake wouldn't have helped either because the driveshaft failed on the nearly new truck and ripped out the air lines.
     
  9. Hip_Shot_Hanna

    Hip_Shot_Hanna Well-Known Member

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    With the introduction of disc brakes on trucks there should be far fewer run aways , they are far mor efective at loosing heat than a drum brake , though there are drawbacks as drivers find out that they can abuse the brakes far more than they can with drums , i have seen the paint burnt off wheels on trucks fitted with discs !!
     
  10. james dilley

    james dilley Well-Known Member Supporter

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    First off Jake brakes are just a auxillary type of brake, And yes they do rely on the valve train of the engine to work. But lest we forget they are a Electronicaly controlled now. and your thoughts are on the money for the most partI can and do drive without using one thought as for what if they fail???? just think of that.
     
  11. Darren

    Darren Still an :censored:

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    I've seen the rotor on a Paystar with front disk brakes melt. Apparently the caliper froze and the trucker couldn't tell the brake was actuated. There was a heavy stream of sparks coming from underneath the truck. I signaled the trucker and he pulled over. There was nothing left under the caliper. I'm not sure disk brakes are a guarantee of no runaways