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Old 05-24-2022, 06:35 AM   #1
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Join Date: Feb 2021
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MT 40 retarder

Problem… A newly rebuilt Allison MT40 trans in a ‘73 Bluebird Wanderlodge retarder is not working.According to the mechanic, he’s been consulting with Allison, and an “older mechanic” who has worked on transmissions. He is in his ‘70’s as I am. Mechanic is in his mid 30’s so the whole rig is older than him. We found an Allison Trans. adjustment tool which helped adjust shift points but didn’t fix the retarder issue. He said that there are some vacuum lines or some kind of issue that may have to do with the engine, a 391 Ford. My question is….are there vacuum lines or whatever that could cause the retarder not to work on an MT40? Any suggestions on anything to look for or check? Mechanic said he is determined to get this working. As some of you know it’s getting harder to find shops that will even work on these older units. The shop works on busses, trucks, motorhomes.Thanks for any input.
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Old 05-24-2022, 04:30 PM   #2
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Join Date: Mar 2021
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Here is an older service manual. There is a section on adjusting the linkage for the retarder. There is a troubleshooting section as well. Maybe this will help.

Also, I don't know if it applies to yours, but Allison mentions in other locations that if there is filter for the hydraulic retarder and it's either plugged or installed on the wrong side this will minimize the retarder's function.
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