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transmission oil type clarification


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My car is a 1948 Chrysler with fluid drive.  My transmission has a drip coming off of it and so I checked the level and sure enough it is low.  I can't find 10W motor oil anywhere in the major auto parts stores.  So what's the difference between that 10W motor oil and SAE 10W oil?  I picked up a couple quarts of the SAE 10W oil and the label says it's for low pressure hydraulic systems and compressors.  It's almost clear as water.  Is that the stuff I'm supposed to be using?  That drip I mentioned on the bottom of my transmission is reddish.  I've heard some guys use auto trans fluid. Is that ok to use?  I'll be draining whatever is in my transmission anyways so as not to mix fluids. 

Another question is I'm curious about the large plug behind the transmission solenoid. (1 1/8") I took it off assuming that's where you'd add the fluid.  Under the plug is a long heavy duty spring that is under tension when the plug is tightened.  The square plug on the side of the transmission about half way up is referred to as the fill plug in the manual, even though I thought it was just the overflow or full indicator.  So I'm guessing it serves two purposes.  You pour the fluid in there with a tube attached to a funnel and when it starts coming back out of the hole around the tube, you know it's full.  But so why not fill from that large plug I talked about? 

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22 minutes ago, timecapsule said:

So what's the difference between that 10W motor oil and SAE 10W oil

Nothing AFAIK. SAE is Society of Automotive Engineers. They write specifications for the auto industry. Your fluid drive is a low pressure hydraulic system. Compared to a real high pressure system like aircraft controls! The ones where you look for leaks with a broom handle. When the handle is cut in two, that's where the leak is.😳

 

They don't want you to fill oil into a hole that is retaining a spring. Maybe the passage does NOT connect directly with the sump. What does the spring do? That would explain where the oil would end  up if added through that hole.

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1 minute ago, Frank DuVal said:

Nothing AFAIK. SAE is Society of Automotive Engineers. They write specifications for the auto industry. Your fluid drive is a low pressure hydraulic system. Compared to a real high pressure system like aircraft controls! The ones where you look for leaks with a broom handle. When the handle is cut in two, that's where the leak is.😳

 

They don't want you to fill oil into a hole that is retaining a spring. Maybe the passage does NOT connect directly with the sump. What does the spring do? That would explain where the oil would end  up if added through that hole.

Yeah, I had the same thought about adding the oil in that large easy access hole with the large plug.  I tried to find a clue in the illustrations in the manual but it wasn't clear as to what's going on with that spring or if like you mentioned if it is connected to the cavity of the transmission.  So I just put the spring and plug back in tight.  That part of my questions was more curiosity.  I'll use the hole on the side to fill it once I'm sure what I should use.  So you're thinking that since my transmission with the fluid drive is low pressure hydraulic, which makes sense since it changes the gears through hydraulic pressure, that the SAE 10W oil that I bought might be the right stuff?

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The 10W oil will be fine. You can use the same thing in the Fluid Drive unit which is filled separately. Use the designated fill plug to check the oil, if you can stick your finger in and touch the oil it is full, if not pour in oil until it drips out. Not sure what the other gadget is, there are 3 electric controls on the trans, a governor, solenoid and switch. Put everything back the way you found it and cross your fingers, chances are you didn't hurt anything.

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7 hours ago, Rusty_OToole said:

The 10W oil will be fine. You can use the same thing in the Fluid Drive unit which is filled separately. Use the designated fill plug to check the oil, if you can stick your finger in and touch the oil it is full, if not pour in oil until it drips out. Not sure what the other gadget is, there are 3 electric controls on the trans, a governor, solenoid and switch. Put everything back the way you found it and cross your fingers, chances are you didn't hurt anything.

Ok thanks. Yeah it's low on fluid for sure.  I put a bent Q-tip in the hole and it came out clean.  Now I have to try and determine where it's leaking.  There are a few side plates on that trans so I've wiped it clean and I'll just have to keep an eye on it.  It might not be the main seal that's leaking. AB has what they call a "transmission gasket set" for the fluid drive set up. But it's only 15 bucks.  That sounds awfully cheap, so I'll call them to see what you get in that kit.  Mopar mall doesn't show a listing for the fluid drive trans, so I'll check my parts catalog and start phoning the suppliers with p/n's I suppose.

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You didn't say whether your cars a daily driver you have for fun or a fully restored beauty...

In years past there were numerous additive compounds that swelled up old leaking seals for people who just wanted a few more miles out of the old buggy that wasn't worth rebuilding the transmission in...(or, nowadays, when the leak worsens, selling the car to a restorer who has deeper pockets0...

I'll get brickbats for suggesting such Mickey-Mousing,  but i used a good quantity of that stuff myself, for both transmissions and power steering, and when the old jalopies died it wasn't becuse of transmissions or power steerings going out...

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If it leaks a little don't worry about it, old cars do that. Check it at every oil change (3000 miles) and top up if necessary. The factory recommended changing trans oil every 10,000 miles, chances are yours has not been changed in many many years.

You may have to take action if the oil is pouring out but if you only have to top it up once or twice a year it's normal.

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14 hours ago, Rusty_OToole said:

If it leaks a little don't worry about it, old cars do that. Check it at every oil change (3000 miles) and top up if necessary. The factory recommended changing trans oil every 10,000 miles, chances are yours has not been changed in many many years.

You may have to take action if the oil is pouring out but if you only have to top it up once or twice a year it's normal.

Yeah I would have been surprised if the bottom of the transmission and oil pan were bone dry.  But at the same time if I can discourage leaking by changing a few gaskets, why not.  I've already got an engine pan gasket set.  I think it would be good to have a look in there to see how things look and get any sludge out of there. That way I should know it the oil coming from the front of the pan is that front oil pan gasket or if it's the the crank seal.

There just doesn't seem to be a trans. oil seal/gasket kit for the fluid drive cars.  In the parts catalog what is the "underdrive" transmission.  It looks very similar to my transmission.  Is that the one used with the fluid drive? 

19 hours ago, Bud Tierney said:

You didn't say whether your cars a daily driver you have for fun or a fully restored beauty...

In years past there were numerous additive compounds that swelled up old leaking seals for people who just wanted a few more miles out of the old buggy that wasn't worth rebuilding the transmission in...(or, nowadays, when the leak worsens, selling the car to a restorer who has deeper pockets0...

I'll get brickbats for suggesting such Mickey-Mousing,  but i used a good quantity of that stuff myself, for both transmissions and power steering, and when the old jalopies died it wasn't becuse of transmissions or power steerings going out...

My car is in excellent condition, but not a show car.  I think other than a paint job and new seat upholstery some time in it's life, it's pretty much original. Other than periodic maintenance such as new brake lines, brake linings, and wheel cylinders, etc.  I don't really see any obvious signs that the transmission/ engine might have been taken out at any time. 

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Before you go any farther you should buy a factory repair manual. It will clear up the question of how many seals and  gaskets there are in the trans, where they are and how hard to replace. A manual will pay for itself many times over in time and money saved.

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On 4/13/2021 at 11:53 PM, timecapsule said:

I have the manual and I have read it. Now I'm here asking the two questions that the manual doesn't answer.

 

1 hour ago, Rusty_OToole said:

Before you go any farther you should buy a factory repair manual. It will clear up the question of how many seals and  gaskets there are in the trans, where they are and how hard to replace. A manual will pay for itself many times over in time and money saved.

He has the manual.

 

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