1940 Transmission leak

19Fordy

19Fordy

Well-known member
What causes the gear oil to leak out the rear of the 40 ford transmission and how can it be fixed? Is it a bearing problem? I took my transmission apart in 1970 but I can't recall the inner details.
Thanks.
 
the counter shaft for the cluster gear as well as the shaft for the reverse idle gear pass through the rear of the case. Both of these shafts are under oil when in use. There is not a seal or gasket in this area that prevents the gear oil from leaking pass the shafts and the case.
 
Terry said:
the counter shaft for the cluster gear as well as the shaft for the reverse idle gear pass through the rear of the case. Both of these shafts are under oil when in use. There is not a seal or gasket in this area that prevents the gear oil from leaking pass the shafts and the case.
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Thank you Terry. Any ideas on how I can fix the leak?
 
There wasa recent thread about oil, if I remember correctly, that mentioned this problem. The shafts held the oil back by clearance fit only. After many years and many miles, the shaft bores fret slightly which causes them to seep. Mac VanPelt mentioned that he uses RTV on the bore fit and for the retaining pin too. Using SAE 140 lube oil in warmer climates helps too with no apparent problems in shifting gears. Colder climates have to revert to SAE 90 lube oil.

Kerby
 
If that is the same trans since 1970,i would guess its not and unsize shaft.The new shafts some have been reported to be under size as much as .002, they should be plus o/minus only .0005
 
rotorwrench said:
There wasa recent thread about oil, if I remember correctly, that mentioned this problem. The shafts held the oil back by clearance fit only. After many years and many miles, the shaft bores fret slightly which causes them to seep. Mac VanPelt mentioned that he uses RTV on the bore fit and for the retaining pin too. Using SAE 140 lube oil in warmer climates helps too with no apparent problems in shifting gears. Colder climates have to revert to SAE 90 lube oil.

Kerby
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I even filled the transmission with 600W and it still leaks. Do I need a new case? Are there measurements I could take to see how much the bore is worn?
 
My pickup has this same problem. You can minimize the amount leaked by running the level 1" below the filler hole. If you do that be sure to check the level frequently.
 
George/Maine said:
If that is the same trans since 1970,i would guess its not and unsize shaft.The new shafts some have been reported to be under size as much as .002, they should be plus o/minus only .0005
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Not sure if I understood your reply, but it's the same original OEM transmission that came with the car in 1940.
 
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I took the shafts in my '39 and machined O-ring grooves in the ends of the shafts and installed O-rings to seal these shafts, now I have a dry floor under the transmission.
 
A while back I read about there being a possibility of a leak around the counter shaft before I rebuilt a box. To hopefully prevent it, the fix was to drill and tap holes in the case around the outside of the counter shaft hole at the front of the trans then RTV it and bolt on a cover plate using the holes. This would fix the front but I don't think you have the room at the rear.
 
19Fordy said:
I even filled the transmission with 600W and it still leaks. Do I need a new case? Are there measurements I could take to see how much the bore is worn?
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I dont think I would put that 600 weight oil in there,that stuff is for early tranmissions with straight cut gears. Its seeping around the shafts as mentioned before. The biggest pain in the rear is having to pull it out to fix it.
 
My forty did the same thing, put all new seals and gaskets in the trans and sealed the two shafts with red rtv. It lasted for quite awhile but eventually leaked again. I would use the o-ring idea.
 
there was a fellow on ebay who sold the two shafts with O-ring seals. I believe he may be out of them at this time. I bought a pair from him and mic-ed them, both were spot on size. it is difficult getting the O-ring installed in the case, force will only cut the O-ring. The trans I installed the rings on does not leak.
 
Terry said:
there was a fellow on ebay who sold the two shafts with O-ring seals. I believe he may be out of them at this time. I bought a pair from him and mic-ed them, both were spot on size. it is difficult getting the O-ring installed in the case, force will only cut the O-ring. The trans I installed the rings on does not leak.
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Terry, Is the groove cut so the 0-rings actually compress so they fit in the transmission case casting hole where the shaft goes?
 
Terry said:
there was a fellow on ebay who sold the two shafts with O-ring seals. I believe he may be out of them at this time. I bought a pair from him and mic-ed them, both were spot on size. it is difficult getting the O-ring installed in the case, force will only cut the O-ring. The trans I installed the rings on does not leak.
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I made a tool to do this with so the o-rings wouldnt get cut as they slide in. Made it out of a piece of round stock that just fits in the hole and ground one end so when its inserted in the case it gives the o-ring something to slide on.Works like a champ.
 
Here's a picture of the cover plate I put on a transmission I rebuilt. RTV is used to seal it all and you just have to make sure that the screws securing the plate do not protrude into the inside of the box. I like the idea of the O-rings. I can see putting an O-ring on the rear end of the cluster gear shaft and one of these type of covers on the engine side. I don't see how you can install O-rings on both end of the shaft without the risk of tearing one. Could you chamfer the rear outside hole and grease it with vaseline so that as you slide the shaft in you would not tear the O-ring?
 

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I O-ring the case, and use Redline MT-90 gear oil, with no leaks and a nice shifting transmission. I cut three grooves, one on the back of the reverse idler shaft bore, and two grooves on the cluster shaft bores. O-ring is 3/32 Buna-N.
Gary
 
Lucas sells some potent stuff for stopping leaks in auto trans and power steering pumps and they work. You might see if they have something for manual trans. It's worth a try before you get your hands dirty. Just a thought. Good luck, Al
 
Hamtown Al said:
Lucas sells some potent stuff for stopping leaks in auto trans and power steering pumps and they work. You might see if they have something for manual trans. It's worth a try before you get your hands dirty. Just a thought. Good luck, Al
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Al. Could you please post the name of the Lucas "stuff" if possible? Thanks.
 
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