Occasionally, someone asks me about our retarder. I always have a difficult time in answering this question.
Anyone care to try to come up with a layman's description I can use in answering that question next time?
Thanks.
George To me the retarder is an auxiliary braking system that's built into the Allison transmission . It uses the transmission fluid acting on a vaned flywheel to induce drag or braking on the rear wheels. This system can be controlled by hand or with the brake peddle .The only down side i know of is that it can raise the transmission fluid temp. Joe
Retarders give you another way to slow down, lessen the need to use the brakes, and reduce brake wear. All retarders can be turned on or off by the driver.
The exhaust brake uses a valve installed on the engine exhaust system to restrict or hold back the engine exhaust. The closed valve causes a buildup of exhaust gases that flows back into the combustion chamber of the cylinders. Pressure buildup in the cylinders creates a power loss by restricting the fuel mixture delivery to the cylinders.
Motorcoach Brake Systems and Safety Technologies (http://beamalarm.com/Documents/motorcoach-brake-systems-and-safety-technologies.htm#RETARDERS)
I like Joe's description.
Another factor I present is that the heat generated by vaned wheel moving transmission fluid is transferred in a heat exchanger to the engine coolant, and discarded via the radiator. To dissipate energy and slow the coach, you turn the energy of motion into heat. Most vehicles heat up the brakes. The retarder allows you to heat up fluids and then get rid of that heat through the radiator. Brakes can easily overheat on a downhill run. The retarder and radiator can send the heat into the air more effectively than the brakes in a long descent.
K.I.S.S. Pull back on little stick (reins)+ horses down, push little stick forward, horses take off. The end.
LDavis,
'01 GV
http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=SA2953EN.pdf (http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=SA2953EN.pdf)
I found this link that has an explanation of how the retarder works. It's the operator's manual for the Allison 3000 and 4000 series transmission. Anyone that does not have the manual could print this out for future reference.
www.rvtechlibrary.com/transmissions/3000_4000_operators.pdf (http://www.rvtechlibrary.com/transmissions/3000_4000_operators.pdf)
There is also some serious stuff about procedures to achieve smoother shifting and a section on fault codes.
The best explanation that I have heard is to imagine the transmission as a backyard swimming pool, with 10 little kids all going in one direction, moving the water in a swirl. When you apply the retarder, you turn some or all of the kids around and make them all move against the water flow ... slowing everything down. I volunteered that explanation at the Ladies Driving School, when one student asked the question ... and for some reason lots of light bulbs went on. The instructor was searching for words that would work for those of us who don't "speak mechanic", and this image helped, I think.
I go this idea from Dave Head.
Think of a large water wheel.
From which I extrapolated: if you think of the large water wheel turning rapidly clockwise and then you are able to slowly or rapidly change the flow of the water hitting the wheel, then you will slow down the movement of the water wheel drive shaft. That image works well for me.