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Transmission woes

953500

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Hi everyone, I have a 95 C3500 with the 6.5 TD. I am having a hard time figuring out why my transmission is not shifting into OD. I have zero idea of what the service records are on the truck, but here's what I do know. I put 2 new matching batteries in 2 months ago, have put new transmission fluid in, and the only other things that have been done is the PMD has been relocated and I removed the garbage air box.
 

JayTheCPA

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Am presuming ". . . put new transmission fluid in . . ." means a flush and not simply adding some. How long since the previous fluid change? If it is unknown or *way* over schedule, this sometimes causes issues from the new fluid cleaning out all the crud.
 

THEFERMANATOR

FRANKENBURBAN
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If the ECM sees engine temps under around 40 degrees, OD is locked out. It's also locked out around 240 degrees engine temp. Cold trans temps and hot will also do the same thing. It's a protection measure to help the engine warm up, or cool it down there are also several codes that will disable OD and not turn the light on in a 95. These are fully electronic transmissions, and thus require electrical diagnostics for most problems. And when you changed the fluid, I hope for your sake you used dex/merc fluid or a dex 3 type, and NOT dex vi fluid. Dex vi(6) is not compatible with older seals and is known to take seals out 6+ months after a fluid change.
 
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