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51 Dodge tranny fluid


Dan Heston

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I have looked through the forum and for the life of me I can't find the answer.  My son and I just finished the reinstall of his rebuilt flathead and tranny.  We need to add tranny fluid but I can't figure out what type of oil to use. I have heard to use 10w gear oil and even someone saying I could use regular 10w 30 motor oil in it.  I hope someone can tell me what to buy so we can take the car out under its own power. Thanks.

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If you have the gyromatic, are you talking about the transmission gearbox oil or the fluid drive fluid.  10W goes in the gearbox of the semi-auto trans.  The fluid drive fluid is a little different.  This has been discussed over and over again.  Many people will just say put 10W in it.  But that is not good advice.  There are many oils you can put in the fluid drive, but you won't get very good performance.  Here is what you will need.  Be sure to order it by the part number.  There are some Mobil oils that look like this, but only this is made with the anti foaming agents that a turbine requires.  

 

https://www.grainger.com/product/4ZF36?RIID=58059293155&GID=&mid=OpenOrders_WillCall&gucid=EMT:10101010:SKU:CSM-348&emcid=NA:SKU

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On 1/17/2021 at 11:18 AM, Worden18 said:

If you have the transmission that goes with the fluid drive unit then use 10w.  It's fairly thin, but that's what it calls for.

Well, that's partly true.  10w oil goes in the gearbox if you have the semi auto transmission, but if he owns a Wayfarer model, that has a fluid drive with a 3 speed manual transmission that takes an 80w oil.  

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19 hours ago, MarcDeSoto said:

Well, that's partly true.  10w oil goes in the gearbox if you have the semi auto transmission, but if he owns a Wayfarer model, that has a fluid drive with a 3 speed manual transmission that takes an 80w oil.  

The period manuals must have some different info on various models.  The manual for my Meadowbrook calls for 10w.  But good observation Marc.  I wouldn't have guessed it could be different for other 3 speed FD models.  I wonder why?

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The semi auto m6 trans has an oil pump in it to cause auto upshifting.

Put 80 weight in it ...

It will upshift for sure but take forever to auto downshift.

It needs 10W oil only.

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Thanks very much for the comments and advice.  I found the AW32 and added that.  Now I have a bit of a dilemma with some grinding when I shift into reverse.  Not forward; only reverse.  The tranny was reinstalled after the engine rebuild and it shifted into reverse fine a few months ago.  The tranny wasn't opened either.

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Did you put a slight wipe of oil on the two pilot bushings in the fluid drive coupling.

Also you didn't let the trans hang and bend the clutch disc when R&R'ing the heavy transmission?

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4 hours ago, Worden18 said:

The period manuals must have some different info on various models.  The manual for my Meadowbrook calls for 10w.  But good observation Marc.  I wouldn't have guessed it could be different for other 3 speed FD models.  I wonder why?

The reason why is this:  In 1941 when Chrysler and DeSoto got semi auto 4 speed transmissions with fluid drive, Dodge just got the fluid drive with a standard manual 3 speed trans.  That lasted until 1948.  then in 1949, Dodge finally put the semi auto M-6 transmission in the longer wheelbase models of Coronet and Meadowbrook.  The smaller low-priced Wayfarer continued to use the fluid drive coupling with a standard 3 speed manual transmission that uses an 80w oil.  Since you haven't told us what transmission or model you own, it's hard to tell you exactly what oil to use.  So use either 10w if you have a Coronet or Meadowbrook, or 80w if you have a Wayfarer with the standard 3 speed.

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He has a 1951 Coronet.

Top of the line Dodge.

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I found the AW32 and put that in.  I have the Fluid Drive, 4spd.  My issue now is the grinding when I try to go into reverse.  I'm trying a few things with linkage and clutch.  I didn't let the tranny hang as we were using a jack to support it during removal and install.

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