Torque Converter wont stay Locked!

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Two days in a row early in the morning when I leave for work Temp around 18 to 20 degrees. The torque converter locks up fine for about 5 miles then will drop down out of OD to 3rd. This happens even at 65 to 70 mph . I can run it up to 75mph and let off the pedal a little and it will shift to OD but as soon as I slow down to 65 it happens again. When I get to town and slow down to 30 to 35mph it shifts to OD and seems to function properly. This only happen in the morning. After work it shifts and operates fine.


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92 Dodge LE, Cummins, reg cab,4X4,3:54 gears, Auto, Black/w Maroon Int.

 

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My truck takes a while to shift into OD when it is cold also. I believe there is a temperature switch in the transmission that keeps it from going into OD until it heats up.

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93 350 Club Cab, Banks Exhaust, 14cm wastegated turbo housing, pump "turned up"to the max, tach, pyrometer, boost guages 98 FATBOY

 

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This may or may not help ya but the transmission has a sensor in it that is suppose to shift the transmission from overdrive to 3rd is a sensor in the transmission registers a temperature greater than 280 degrees. I got that out of the owners manual. Maybe this sensor is going south on ya if your transmission isn't really getting that hot. I'm not sure where this sensor is located. Maybe somebody else can help ya with that one.
Pat Daniels

 

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Thanks Coasty, I'm believing that it is some kind of sensor malfunction. Temp or speed sensor. Becuase the fluid still looks and smells new and everything else seems to operate fine. I was just wondering if any body else has had this problem.
Guess i'll run it to the local dodge dealer and put it on the scope. I'ts always nice to go with as much info as possible.

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92 Dodge LE, Cummins, reg cab,4X4,3:54 gears, Auto, Black/w Maroon Int.

 

[Archive]

Eugene, from my past TPS sensor failures, this sounds like the throttle position sensor acting up. According to my shop manual, the SBEC will hold a failure code in it that can be read at the Dealer. Their is definitely a temperature switch in the transmission that prevents shifting from 3rd to OD when the fluid is either too cold or too hot.
My best investments to date have been the Dodge shop manual and my TDR membership.
'92 D250, LE, auto, stock all the way except for my K & N air filter! 208,000 KM