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ralphnof49

Transmission oil leaks

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My 47 Lincoln transmission leaks oil from several places it seems. One is very unusual as it is a small channel in the case on the passenger side rear corner just above a nut. Oil drips out of the channel and I get quite a lot on the floor after a few hours. The photo shows the channel seen easier with the red plastic tube slid into it. I would like to know what is happening with t his leak. I changed the oil in the transmission last fall and the oil leaking has increased a lot since. Thanks.

IMG_1635.jpg

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Interesting process. My transmission works well so I hope I don't have to go to a rebuild process.

Thanks.

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I guess I would just find out where that hole went and for what purpose.

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That looks like it may be the hole for the lock pin for the counter and main shafts. Look on the driver's side of the transmission to see if there is a pin in the hole and make sure that it is all the way in. It should be seated and then a cotter key inserted in the hole of the pin on the passenger side of the transmission. You may have to raise the rear of the trans and remove the bottom 2 bolts to get at the pin.

 

This pin is necessary and if it is missing, you may have to remove the transmission to get at the counter shaft so the hole in it will line up with the hole in the main shaft.

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The shafts should fit in the case tight enough so that gear oil doesn't leak past them. If it is only coming from the lock pin, you can remove the pin, clean the pin and the casting and then use a non-hardening gasket sealer in the holes and then push the locking rod back in. That should stop the leak. If it is leaking from the shaft holes as well, you will have to pull the transmission and rebuild it. When the casting is clean and dry, you can coat the shaft ends with thread locker just before you seat them in the casting. This usually seals them.

 

A 140 gear oil may not leak as fast as the multi viscosity oil. Sta-Lube makes a 150 oil.

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When I probe the hole it only goes a very short distance (1/2 in) and seems to curve up a little. There is no pin on either side at the location of the hole. My 46 parts car transmission has the same hole which was covered by oily dirt. I am going to drive a short way and check for oil leaks again.

Thanks for the ideas.

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Posted (edited)

There should be a pin right thru from one side to other as per 40 Zephyr sedan picture. Yours could be missing altogether.  The pin locates the two shafts  which hold the cluster gears and reverse idler gear  inside transmission. I would not drive vehicle without pin in position. The shafts could slide forward or back and gears could drop out of mesh!!  The upward curve 1/2 inch in hole could be shaft has spun and pin hole is on angle .Cant  figure out what the nut like shape is for in  ralphnof49  pic. Those shafts all ways leak some oil!  " O" rings can be fitted, the groove edges need to be  shamfered to be successful otherwise the "0" Ring  can be damaged  during assembly.  My 40 Ford G/box  was done recently, runs bone dry on outside. Trans has to be dismantled to machine   O ring  grooves!

Edited by 38ShortopConv. (see edit history)

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I agree that you should not drive it without the lock pin. If the counter shaft shifts enough for the gear to drop out of place, it could break the case. You can try to rotate the shafts into alignment by using a small drift or similar probe. The lock pin is available from some of the V-8 Ford suppliers. If yours is an overdrive trans, it will be more difficult to get at the pin. I am not sure about the Lincoln, but you cannot remove the side cover on a Ford or Mercury without removing the trans. There is not enough room to get the forks out of the case. If the counter shaft has moved forward, you will have to remove the trans in order to push it back in place.

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The post war setup is different. It is correct that the hole is for the pin. The other side of the hole is under the cover on the side of the transmission. We pulled the trans out of my 46 parts car to see how it is set up; the pin is simply pressed in and has no cotter pin. The end of the pin under the cover has about 1/4 inch space between it and the case so it is possible for  it to shift out a bit and allow oil to leak out. Attached is a picture of the pin. I am thinking of putting a short piece of metal in to keep the pin from shifting again.

I am also exploring the best way to take the cover off the trans still in my car.

IMG_1637.jpg

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The oil is leaking around the one or both of the shafts, keeping the lock pin in place will not stop the leak. I think that the setup you described is for the overdrive transmission.

 

You said that the leak got worse after you changed the oil. Are you sure that you did not overfill the gear box? It should be filled just enough so that when you put your finger in the hole and bend the top joint of your finger you can just touch the oil.  Remove the filler plug and let the excess oil drain for about 15 min at 70F, and longer at lower temperatures. Did you use a GL4 90W?

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Yes the transmission does have the overdrive. The oil may have been a little over full but still below the filler hole. It is at the level you recommend now. The oil I added was a synthetic 75 to 90W. My plan now is to seal the hole for the pin rather than removing the cover and trying to keep the pin tight against the hole. 

Thanks for your help.

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Here is what Mac VanPeltz had to say about the type of leak that you are having:

 

We do not use the o rings on the shafts. Typically they get rolled or cut during installation. Plus you've now cut a groove in the shaft, potentially weakening the steel. Also, the shafts do not wear at the ends where they sit in the case bores. Remember, the shafts are stationary.

We have the advantage of working with totally clean & dry gearbox castings, so sealing up the shaft ends is a simple matter of a final wipe with brake clean and spreading RTV sealer around the shaft ends.

Going a step further, we clean the hole for the lockpin with the cleaner on a Q-tip. Inject some RTV into one end of the opening, smear some on the lockpin, and tap the pin into place. Let it sit overnight before finishing up the job and adding any gear oil.

When you install the trans, you'll be making a connection to the torque tube (if closed drive). Use a thin layer of RTV on clean parts before adding the gaskets. The gasket sets come with a length of cork for use as a seal at the rear opening of the split cap assy. Some guys have tried using some oil resistant rubber tubing instead. I don't know how well this works.

We've done MANY trannies and found these things to help control the leakage. Stay away from synthetic gear oil.....it seems to find the tiny openings easily on its way to your garage floor.
 
 
 
I would drain the transmission and fill it with SAE 90 GL4 oil.

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Thank you That is good information, I will try to find the oil you suggest. I am using sealant on the hole and it is working well. 

I also had leakage where the solenoid shaft goes ito the transmission and added an O ring which has helped a lot.

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NAPA should be able to order it if they don't have it in stock.

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