Engine Brake

[Cathy&Paula]

I am a little confused on this engine brake thing. I keep hearing jake brake, engine brake, exhaust brake, auxiliary brake, engine retarder. Are all these things the same thing??

I think I have an engine brake because that is what is on the button that I push but when it is engaged it says auxiliary brake. I have only used it a few times but I am know in Colorado and need it more but I am not sure if I am using it right. When the brake is on I can fell the MH jerk when I let off the gas and when I am going down hill the gear goes down to 2nd is this suppose to happen. I was told to downshift as I go down the hill but how much do I downshift and how can I downshift if it goes into 2nd automatically. I know I am not suppose to ride my brakes but it is a little scary and I don't think the engine brake is slowing me down enough.

Any advise as to how this thing works and how I am suppose to use it would help.


Thanks
Cathy

[bigskymt]

You probably have a Pac Brake, a valve in the exhaust that uses the engine to slow down. If it were a Jake brake you would likely have different settings like 2,4,6 or lo,hi.
Jake Brake refers to a Jacogs Engine Brake that opens exhaust valves in the cylinder heads for braking. Retarder was the old Caterpillar brake before Jacobs made one for Cat.
Our Newmar KSDP w/Cat will auto downshift the trans. with brake on. I think it will show "2" as that is as low as it will downshift while braking.
Releasing the accelerator will activate the exhaust brake, "feathering" the pedal will activate/deactivate the exhaust brake.
In the mountains we use the exhaust brake and apply foot brakes as required to keep RPMs down below 2200.........just my preferrence.
I wouldn't bother to downshift.
There are plenty of DP owners here that can explain it better.

[W8RLM]

I'm not familiar with Dutch Star, but it sounds like you have an exhaust brake. If you have the switch on, when you release the accelerator, the exhaust brake automatically engages. A "flap" closes the exhaust, and the fuel is shut off. The engine compression now works against the forward motion of the motorhome and acts as a brake. The transmission is programmed to downshift to get to 2nd gear as fast as possible. The limiting factor is the computer which calculates how high the engine RPM would be as it downshifts from gear to gear. It will prevent the downshift until the speed of the coach is slow enough that the engine will not overspeed. Therefore, on steep grades, you may have to use the service brake to help slow down the motorhome until the computer calculates that the downshift safely. I believe that the CAT diesel limits to 2500 RPM. The older style transmission controls have only one window to show gear information. The engine brake will cause the display to show "2". That is the goal of the system - get to 2nd gear as soon as possible. My CAT manual says that you can use the exhaust brake as often as you want. The engine and transmission computers prevent any damage.

As far as downshifting is concerned, you can downshift anytime that you want, but if the downshift would result in overspeeding the engine, then the computer will prevent the shift.

There are several sites that can explain the differences between jake brakes, etc.

Hope this helps.

W8RLM - Bob

[Dennis M]

An exhaust brake is usually an aftermarket installation while an engine brake is designed into the chassis and usually more effective. I expect that you have a real engine brake.

"Jake" is slang for Jacobs Brake Co. that manufactured exhaust brakes.

In real life the terms are usually used interchangeably. Either one will provide additional engine retardation (not actual braking) when you lift off the throttle.

The old rule of thumb in the mountains is to go down one gear lower than you came up, although with todays more powerful engines two gears down might be better.

Do not worry about going too slow! Decide on the speed you want (it's a good idea to go by the truck speed limit), let the engine brake hold you back and the speed to build until you are 5 or 10 MPH over your desired speed, then hit your service (foot) brake hard and bring the speed back down below your target speed. Then get off the brakes and let them cool as your speed builds back up again - repeat as needed. No need to worry about overheating the brakes if you give them enough time to cool between applications.

If I select my gears right I can often get down a mountain on the engine brake only without using the service brake, and we weigh 37,000 lbs.

The most important rule is do not ride the service brake. Use it as needed to scrub off speed, but then give them time to cool before you use them again.

A little practice and you will do fine. Just remember, you are big and people will go around you, don't go any faster than you are comfortable with.

["007"]

Here is a explanation of PAC-BRAKE operation if it applies to you may help.
Another tip found in Quick Tips.

[GaryKD]

Hi Cathy,
Forget what is printed on the button. Newmar uses the same button in several different coaches. If you coach has a Cummins ISC engine, you have a Jake brake or similar brake. This was explained in the previous posts. If you have a Cummins ISL engine you could have a Jake or engine brake. It really does not matter which technology is being used. As long as you understand the concept, you're good to go. I have 63 feet and 37+K total lbs of weight. My Jake brake will hold my coach on grades of 7% or less at 50 MPH without use of the service brake. Steeper down grades require "stabbing" (like in the Hitchcock movie) the service brake every now and then to hold the coach at a speed I feel comfortable.

Know your maximum RPMs and do not exceed the maximum RPMs. If you do, the tranny may upshift to protect the engine. This is not something one wants to happen on a downgrade.

[Parkerrs]

Dennis and Gary have the hill decent with an engine brake dead on regardless of the type. There are two types regardless of the name brand, Jacobs or "Jake Brake" are a brand.

Exhaust brake - This is located in the exhaust after the turbo, usually on it's outlet. It contains a butterfly valve operated by either an air cylinder on the outside or an electric solenoid in some smaller applications. When activated and you release the accelerator pedal the butterfly closes blocking most of the exhaust gas from escaping the engine. This back up of pressure make it hard for the engine to spin. Therfore the backpressure retards the engine which slows your coach through the transmission and differential. Similar to taking your foot off the gas in a car, Diesels don't have the natural back pressure of a gasoline engine.

Engine brake - this device is installed between the head and valve cover of the engine. It has electronically actuated valves between the rockers and valve stems essentially. When activated and you release the throttle, this device does not allow the exhaust valves on the engine cylinders to completely open, holding exhaust gases within the cylinders and essentially turning your engine into an air compressor to slow its rpm. this slows the vehicle through the drivetrain as the exhaust brake does. Engine brakes can have one setting but usually have more. High and low is a two stage brake, one setting allows the valves to open more and create less back pressure and less braking. This is the low setting. Road tractors have a 3stage brake available, high, med, and low,

Hope this helps clarify from an ex- truck driver and heavy truck equipment mechanic. I haven't done either in ten years.

Tommy

[Cathy&Paula]

Thanks for all the information, I have been reading everything I can find on this issue and I have read all the manuals that came with my coach. I do not have all the manuals seeing as I bought my coach used and all the information was not available. I am never in a hurry to get where we are going especially down the side of a mountain. I just want to make sure that I am not doing damage to the transmission or the breaks as I am driving because it does fill alot different with the engine break on, I guess I will have to just get use to it.

I love the scenery here is Colorado but I think I will be glad to get to some flat driving for awhile. Ha Ha

Thanks