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1931 series 90 transmission oil


zimwiz
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I dont want to start any trouble here  but what about the gl 5 factor    harmful  on bronze bushings ?  I know its almost impossible

to get to a conclusion  but I found some  good explanation online that made me change my mind and I found gl3 at napa.

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I have a 1922 Dodge touring that calls out 600W.  It has the same style non synchro gearbox as in my 1925 Buick.   I wanted to replace the transmission fluid with what was used in the past.  I found the 600W so thick, that the transmission had an extremely hard time with shifting.  So bad, that I had to start off in gear and let the clutch out, because it would not let you go into gear from a stand still.  There was either so much drag that nothing slowed down to get the gears to engage, or more likely, that there is so much syrup, that the gears can not rotate fast enough when the teeth get near, and it just wants to grind going in.  I can't imagine how thick this stuff would be in real cold weather.  I did a lot of research (and there are also a lot of opinions).  I drained it out and I put in "MT-90" made by Red Line synthetic.  It is a manual transmission fluid.  It is available many places, but I bought it off Amazon.  It is an API GL-4 so it will not hurt any bronze/brass etc.  It is SAE 75W90.  No problem with seal leakage, and it really shifts well.  I like having the added protection and longer life from a modern synthetic oil.  

 

For the rear axle, you can use just about anything.  No brass/bronze here.  I just use Castrol 80W-90.  You could use 90W-140, and just about any brand would do.   

 

Best Regards,

Hugh

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The brass and bronze issues regarding using GL-4  vs GL-5 come into place with synchronizers in newer manual transmissions.  They are usually a sintered metal actually, but have the brass and bronze particles in them.  But you don't have any of this in your rear axle,  The rear axle does have a hypoid gear, so you can use an EP gear oil (extreme pressure).  All the bearings are steel ball or steel roller style. 

 

There are 2 notes in the maintenance manual for my 1925 Buick for the transmission.  One says to change the trans oil twice a year.  The other note says "A good grade of steam cylinder oil should be used, but at the beginning of the winter season it is advisable to thin the lubricant by adding a quantity of engine oil. "  It does not say how much to add, but hints that you may not like 600W.

 

In the differential section, it says "The old oil should be drained off, differential washed out with gasoline or kerosene and fresh oil introduced twice a season.  Who has the time for this?  My differential was already cleaned when I got my car, and the transmission was out, but when I pulled the top off my transmission, the oil was pretty mucky and looked like taking the valve cover off an old engine where the oil is all caked up inside.

 

 I would think that just about any gear oil today is far superior to what was available in the past.

Edited by gr8success (see edit history)
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   Napa      has    Sta-Lube  brand Hypoid  SAE  85W90    gear oil    API   GL 4   wich is safe on brass and bronze ,  the yellow metals

       After reading all of the opinions   online  I finally  came to agree that this is the best I found.

 .

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While I called them shims,  they fit between the carrier housing and the the spur gears.  They act as a thrust bearing when the spur gears turn.  There are brass synchronizers in the the late 31 and all 32 transmissions.

 

With GL4 and other non GL5 readily lubes available, why take the chance?

 

Bob Engle

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