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| If you have a 640 Allison, what you are describing is probably the converter lock-up clutch engaging. The rpm that this happens is usually adjustable (the pan has to be dropped to do this). If this shifting is really obnoxious, the lock-up pressure port can be plumbed to the pan. This was done a lot in oil well servicing rigs with Allison transmissions. A 12 volt solenoid valve was used so that the lock-up clutch would work when on the road. In your case a switch in cab would allow you to override the lock-up. The transmission might not up shift without the lock-up clutch operational and Allison did not allow this when on the road. A close eye on the temperature gauge would be a good idea when doing this, because never allowing the converter to lock up can cause overheating. | |
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auto tranny in fl70 semi
