Re: Need to know how to properly use retarder with 3406 trans
Reply #10 –
The retarder is on the output side of the transmission, therefore how much retarding it can do is totally dependent on the speed of the vehicle. The braking effect increases with vehicle speed. It's a vaned rotor in a vaned housing with a variable amount of transmission fluid from none to full. When the rotor is turning it heats up the fluid. Maximum braking effect and temperature occurs with a housing full of fluid. At slow enough speeds the housing can be full of fluid and it will not overheat. At high speeds the fluid can overheat with only a partial amount of fluid in the housing. There are varying opinions on how high the temperature can be. I personally try to keep the temperature from exceeding 250 although I doubt if much harm would be done with a short excursion to 300. Your transmission manual may state the max temperature. One has to take quick glances at the temperature gauge and at the same time keep the coach in the middle of the lane on that curving road.
What works for me when descending a mountain or long hill is to select about 1/2 on the joy stick if I am traveling at 40 - 50 mph. From experience I know that more joy stick will soon result in the transmission temperature being too high. This is a good starting point to begin with, then you can add or decrease joy stick position to control braking effect and/or temperature. How steep the road is and how fast you can safely go will determine which gear you need to use. You just have to vary the gear selection, speed, and joy stick position to keep the transmission temperature from overheating. Even if you have selected a lower gear than 6 the transmission can still and will upshift to prevent an engine overspeed that can destroy the engine. Also the retarder will empty if the temperature becomes too high for too long to protect the fluid. Both conditions result in a loss of braking effect when it is really needed. This will really surprise the driver and his initial impression will be that something has failed. The only recourse is to get on the brakes really hard to slow down so that a lower gear will be selected. The transmission is smart enough that it knows to downshift when you are applying the brakes. With the transmission in a lower gear it will not upshift until you apply throttle or engine rpm becomes too high. Manually selecting a lower gear usually results in a downshift unless engine rpm is too high. Also a manually selected lower gear will keep the transmission from upshifting above that gear unless rpm becomes too high. All this applies to the 6 speed Allison World transmission. Other transmissions may be different.
Hope this helps.
Topic: Need to know how to properly use retarder with 3406 trans (Read 1276 times)
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