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Flushing Oil?


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Working on the transmission of my 1932 Dodge DL and in the owner's manual it mentions under maintenance drian the transmission case and then clean out the  case once every six months with "flushing oil" before refilling with the correct lubricant.  This is a new one to me.  I was wondering if it meant kerosene, but a few paragraphs down it again mentions using "flushing oil not kerosene" to clean the case.  Any idea what flushing oil is or where to find such a thing?

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AMSOIL makes a flushing oil for both engine and transmission.  Basically it is oil with cleaning agents.

Professional shops use a machine to pump the oil. The idea is so the whole system gets cleaned.  There are a variety of opinions about that on the Internet, including only if you have signs of problems like slipping, hesitation, etc.

What your manual suggests seems more like an oil change.  As best as I can remember the general "modern" rule of thumb is 30,000 miles or two years.

I have every fluid changed when I first buy a classic... no matter what. 

Edited by Phillip Cole (see edit history)
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Thanks for the reply, Phillip.  The book is, indeed, talking about an oil change, but here is what the book says -


"It is recommended that the oil be changed in the transmission after the first 500 miles (800 km.) of driving and the transmission be thoroughly washed out with a flushing oil (not kerosene).   The transmission should then be refilled to the level of the filler plug on the right side with the proper lubricant.  It is recommended that the lubricant in the transmission be removed, the transmission case flushed and new lubricant installed every six month thereafter."


They obviously mean some sort of solution that was used to clean the inside of the case.  I wonder what it was?  I don't intend to disassemble my transmission because it was working fine and the gears look pretty good, but I would like to clean out the gunk that has been in there for at least 40 years before I replace the top and paint the unit.  I currently have it sitting upside down draining out as much of the old lubricant as I can.  It's pretty tough to get anything down into the case to clean out the sludge at the bottom and I'm looking for a safe solvent that won't damage bearings or seals.





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As mentioned above:  ATF, automatic transmission fluid has lubricity, and is very high detergent.  And it is reasonably priced for an automotive lubricant.  Many modern standard-shift transmissions use ATF instead of 90wt gear oil.  


Looking at the photo of the exposed main shaft of the trans, it looks very clean.  I'd look with a flashlight into the bottom of the transmission case, and see if there is a lot of crud deposited there.   The straight gear transmissions did not generate a lot of crud, since there is nothing wearing away, unlike in an automatic transmission.  


You might find very little on the bottom of the transmission case.  



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