Mack Engine Brake Operation Question

[75CF611]

My 75 CF-600 has the factory engine brake I have always called them jake brakes but I know that mack calles them something else. How is it supposed to work mine dosent feel like it does anything. I know that the switch has to be in the dry road position but that is all I know. Can anyone tell me how this system is suppose to work.

[mackkid]

My 75 CF-600 has the factory engine brake I have always called them jake brakes but I know that mack calles them something else. How is it supposed to work mine dosen't feel like it does anything. I know that the switch has to be in the dry road position but that is all I know. Can anyone tell me how this system is suppose to work.

That would be the Mack Dynatard.The engine model number will have a B in it eg.675entb on the plate behind the fuel pump on the block.

The jacobs brake system is entirely different being a bolt on system. These are easy to pick as they use a spacer between the block and rocker cover. Altho some early Macks were fitted with jacobs brakes Mack developed their own system calling it the Dynatard..

With any engine brake the engine is basicly turned into a compressor

Without going on for hours this is my understanding.

The Dynatard uses a special profile on the cam lobe of the exhaust valves

When the system is engaged basicly oil is pumped into a piston in the rocker thus giving zero clearance between the rocker and valve. This opens the exhaust valve just before top dead centre on the compression stroke. This already compressed air flowing thru the manifold and turbo increases charging pressure into the engine. This increased flow gives the retardation.

You should be able to hear it if it's working! Check you have power to the solenoids (on top of the rocker cover) when the system is switched on.

Hope this helps a little

Steve

[maxidyne237]

are you sure you are not looking at the front brake limiting valve?

[75CF611]

are you sure you are not looking at the front brake limiting valve?

I don't know for sure what is the front brake limiting valve. In the console where the pump engage switch, e-brake, and battery switch is another switch. It has a plat that says dry road and slippery road on it and it is an air switch. We have a 05 FFA pumper tanker at the dept that has a jake brake and the onn/off switch is labeled the same way so I thought that is what it was. I need to trace the air line and see where it goes. I do have an air line that goes in to a maifold that comes out the head and has the coolent filter and the upper raidator hose connected to it. Does anybody know what that is for. I will try to get some pics of the setup in the next day or 2.

[75CF611]

Ok I got some pics the first one is of the switch and the second one is where we think it goes into the engine. If anyone knows what that is on the motor let me know.

[MACKS]

That switch has nothing to do with an engin brake,it limits or shuts off the air to the front brakes so when in the slippery position your front brakes wont work,this prevents them from locking up on wet or icey roads,are you sure you have an engine brake should be a wire going to the top of each valve cover,not sure about that other thing on the motor maybe some kind of temp senser,do you have shutters on the radiator.

[75CF611]

That switch has nothing to do with an engin brake,it limits or shuts off the air to the front brakes so when in the slippery position your front brakes wont work,this prevents them from locking up on wet or icey roads,are you sure you have an engine brake should be a wire going to the top of each valve cover,not sure about that other thing on the motor maybe some kind of temp senser,do you have shutters on the radiator.

There are not any wires going into the engine cover so I guess we don't have an engine brake but thats alright weren not pulling that much weight anyway. Yes the raidator has shutters on it but it has been a long while since they last worked. Where would the valve that works them located at. Thanks fo all the help.

[Rob]

There are not any wires going into the engine cover so I guess we don't have an engine brake but thats alright weren not pulling that much weight anyway. Yes the raidator has shutters on it but it has been a long while since they last worked. Where would the valve that works them located at. Thanks fo all the help.

In the photo you posted on the right there is a valve that is screwed into the water manifold. It is shown with a black plastic line with flaking red paint. That line will run to the air shutter cylinder that is mounted on the radiator frame someplace. That valve is called a "shutterstat". There are different temperature ratings for them and I'm not really familiar with fire apparatus so no real help there. There is also a valve mounted someplace that is an air pressure regulator that leads to the opposite side of the "shutterstat". When the temperature is attained, the "shutterstat" switches positions internally, exhausts the air in the line to the cylinder and the shutter springs return the shutter blades to the open position. By default they are in the open position as you can tell when there is no air in the tanks. When the engine temperature falls to under the setting of the "shutterstat", the valve switches positions again, charges the air line to the cylinder and the shutter blades close.

Pretty simple rudimentary system that they had to improve. Only worked for about 75 years or so.

Rob

[HK Trucking]

That looks like a heat exchanger in the top radiator hose, and those copper lines look like water lines , could those be water lines from the fire pump or tank to give supplemental cooling when the engine is working hard pumping water at a fire scene?

[75CF611]

That looks like a heat exchanger in the top radiator hose, and those copper lines look like water lines , could those be water lines from the fire pump or tank to give supplemental cooling when the engine is working hard pumping water at a fire scene?

Could be, I know that the pump is cooled by the coolant. I think one of them go to the in cab heater as well.

[mackdaddy]

In the photo you posted on the right there is a valve that is screwed into the water manifold. It is shown with a black plastic line with flaking red paint. That line will run to the air shutter cylinder that is mounted on the radiator frame someplace. That valve is called a "shutterstat". There are different temperature ratings for them and I'm not really familiar with fire apparatus so no real help there. There is also a valve mounted someplace that is an air pressure regulator that leads to the opposite side of the "shutterstat". When the temperature is attained, the "shutterstat" switches positions internally, exhausts the air in the line to the cylinder and the shutter springs return the shutter blades to the open position. By default they are in the open position as you can tell when there is no air in the tanks. When the engine temperature falls to under the setting of the "shutterstat", the valve switches positions again, charges the air line to the cylinder and the shutter blades close.

Pretty simple rudimentary system that they had to improve. Only worked for about 75 years or so.

Rob

Regarding the position of the shutters when there is no air in the tank. Mack has it where the shutters are open but I have noticed older KW and Petes where the shutters are closed until you air up. Just switching the hoses or is the shutters built differently? I always thought it a better idea to have them open with no air so if you were pulling a hill and lost air or hose you would not over heat.

[Rob]

Regarding the position of the shutters when there is no air in the tank. Mack has it where the shutters are open but I have noticed older KW and Petes where the shutters are closed until you air up. Just switching the hoses or is the shutters built differently? I always thought it a better idea to have them open with no air so if you were pulling a hill and lost air or hose you would not over heat.

Hi Dan,

I've never seen a shutter system that was default closed by design myself. It does not make good sense to me for them to operate that way because they cut off at least 95% of free airflow through the coil, (radiator) when closed. On Mack trucks there is always a pair of extension springs attached through linkage to pull the shutters open upon either a drop in air pressure to the operating cylinder, or the shutterstat dumps the air supply to them.

I have seen spring balanced, air actuated cylinders in usage that were default closed, but not in an on road truck application.

Engine overheating would certainly occur if the shutters were not allowed to open in warmer temps.

Rob

[theakerstwo]

All air operated shutters that i have seen on trucks or air closed but with the Kysor system that has a temp control bulb in the rad that controls the shutters by a manual linkage the shutters will be spring loaded closed. So if the bulb fails then you have a over heat problem unless you have a shut down system on the engine.

[Mack2012]

I have a 2012 mp8 the engine break isn't working nor is the eng oil temp gauge I replaced the eng oil sensor on side of eng by filters and also eng oil lvl sensor. I am currently at a loss as what to look at next

[Joey Mack]

I beleive the engine brake will not operate below 150 degree's. so mabey the temp gauge issue is telling the ECM to dissable the engine brakes... jojo