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Trans Retarder
I’m asking for a friend, Really, who’s not on the forum.
He has an 01 H3, 150k miles, with a Transmission Retarder, He says after approx 30-45 minutes of driving, the Retarder stops working. The next day, it will work again for a while, and then quit again.
Any Ideas? I know the brake and accelorator, and stalk control have an input but not sure where to start.
Also, is it true that the air regulator (that looks like the one on the engine air bags) which is mounted on the bulkhead right across from the starter inside the engine bay door, about the same height as the power steering reservor……..I’ve heard it is for the Retarder as well? IF so, what should the pressure be set at?
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6 Replies
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Jerry, my engine and trans are of the same vintage. The retarder will shut itself off if it detects that the trans is too hot. If trans is not running hot, perhaps there is a bad temp sensor in the system. The transmissions of this vintage have the temp sensor in the sump, which tends to read a lot hotter than elsewhere in the trans. Later Allisons moved the sensor from the sump, so presumably there was an issue with locating it there. I don’t beleive there is any air line involved in the retarder operation. It is all electro-mechanical.
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I agree with Bryan and suggest monitoring the transmission temperature. His coach should have the digital readout on the message center and if in fact the temperature is high (I have no clue what the set point is, but correct temp should track engine temp) then do a transmission fluid level check using the key pad. If temps are OK then look to the sensors.
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Any high temp should turn on the warning light on the Telltale.
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I think that there is an air line going to the accumulator. Sure looks like it on mine. I think that is what forces the fluid out of the accumulator.
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The Allison transmission retarder uses an accumulator that is mounted on the frame next to the retarder. It is fed with accessory air pressure and it is used to put pressure on the accumulator diaphram to cause transmission fluid to be directed against the retarder impeller to give you retardation. Asnoted in the above replies it has a maximum temperature that it should go to and if gone over will put the “check trans” light on in the dash and drop the retarder to protect it.
For the retarder to function the transmission needs to be in lock up (not on converter) and it has to see a 0 percent throttle to function. If it works for a while and then stops working it may ned to have the connections looked at on the device at the accumulator that is siggnalled to allow the air pressure to turn on the retarder.
Here is a the pneumatic diagram section for the pressure regulator at the rear of the vehicle.
The retarder control valve by the transmission ihas both air pressure to it and an electrical harness for the signal from the transmission computer.
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Good info Prevost Service, I guess first easy check would be to verify 80 psi at the regulator, then go from there.
He says he is not getting any lights on, and trans is not getting hot.
Below is pic of the air regulator for the retarder on my bus.
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