39 transmission leak

M

marko39

Well-known member
After finally getting engine and ****** installed I found ****** leak in back where pin goes through the two shafts. It is leaking on the right side of pin which is loose, i can move it left to right. It doesnt seem this pin would wear but why would it leak and would a new pin stop it? It looks like I could push out the old pin with a new one as I really dont want to take everything apart again. I may try to seal pin with permatex but don't think it will work. I know others have had the same problem and has anyone been able to fix this leak with ****** in car?
 
Are you sure that is where the leak is? I was looking at trans parts the other night and noticed Michael at Next Gen Auto is offering a sealed rear bearing for the rear output to help eliminate leaks. It sounds like you are probably right about the shaft leaking but seeing that bearing offered made me wonder if it was dripping downward toward the shaft
 
I think you will find that the leak is between the housing and shafts that hold the cluster gear and the reverse idler. It is very common for them to leak there. Some have cut a groove in the shafts for o-rings where they seat in the housing.
 
40cpe said:
I think you will find that the leak is between the housing and shafts that hold the cluster gear and the reverse idler. It is very common for them to leak there. Some have cut a groove in the shafts for o-rings where they seat in the housing.
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The leak is deffently coming the pin, I have car on lift and been watching it for a week. I rebuilt this ****** a few years ago and did seal the ends of the shafts with rtv and they are not leaking. I wish I paid attention to that pin at that time.
 
remove the pin, clean it and the hole thru the trans with brake cleaner, coat the pin/hole with non hardening Permatex #2 I think and then put the pin back in. I did this with my 41 truck and it seems to work. The leak really is the shafts coming thru the case but this worked for me
 
marko39 said:
The leak is deffently coming the pin, I have car on lift and been watching it for a week. I rebuilt this ****** a few years ago and did seal the ends of the shafts with rtv and they are not leaking. I wish I paid attention to that pin at that time.
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The oil is leaking past the shafts inward of the pin hole and running down/out on the pin.
 
My fix on this... #11 O ring, .750 ODx .562 ID, cut 1/8" groove deep enough that only .007-.010 of O ring is above shaft. Doesn't take much to make a seal.
 

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alanwoodieman said:
remove the pin, clean it and the hole thru the trans with brake cleaner, coat the pin/hole with non hardening Permatex #2 I think and then put the pin back in. I did this with my 41 truck and it seems to work. The leak really is the shafts coming thru the case but this worked for me
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i did this (after draining ******) and its been 4 years with no leaks. i did have to seal the ends of the two shafts again also.
 
The best way is to cut "O" ring groves in the case. Problem solved forever!
Unfortunately, you will have to remove and disassemble the Transmission. Best of luck!
 

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I've put o-ring grooves in the shafts like Big Deuce does - works great. You can try the various bandaid approaches and you might get lucky . . . at least for awhile.

Question: Did you buy and install aftermarket repop main and reverse shafts when you rebuilt the trans?
 
Bored&Stroked said:
I've put o-ring grooves in the shafts like Big Deuce does - works great. You can try the various bandaid approaches and you might get lucky . . . at least for awhile.

Question: Did you buy and install aftermarket repop main and reverse shafts when you rebuilt the trans?
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New shafts came with the rebuild kit I used, the old ones didn’t leak I should have reused them but we all know new is better.(ha!)
 
That's probably why you have leaks. Bored&Stroked has shed bright light on this subject in this forum. Hopefully he will post his findings on OEM shafts vs. aftermarket... the cluster shaft possibly could be swapped out, pushing it out with your old existing one. The reverse idler would have to have the shifter top removed, and recover the pushed through one with a magnetic stick of sorts.
 
marko39 said:
New shafts came with the rebuild kit I used, the old ones didn’t leak I should have reused them but we all know new is better.(ha!)
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I've not found a source for repop shafts that are worth a crap. The two problems I've seen are:

1) They are NOT the correct size -- usually about .001 undersize (this contributes to the leak issue).

2) Inferior material and rockwell hardness: I have no clue as to what material they are made of, but they are not as hard nor precision ground anywhere near as to what the originals were.

With them being smaller and softer, there is no way they are even close to as good as the originals. I will not use repop shafts! I made my own out of Thompson linear shafting - have been great so far.

Another option: Take the original shafts and "flip" them 180 degrees. This puts the bearing thrust on a "good side" of the shaft. This is totally acceptable if the shafts are not all worn out on both sides.
 
Bored & stroked, what series Thompson shafting did you use? Was the material the correct dimension, and where did you source the material?
Thanx,
Tom
 
if you have the trans out and stripped to machine in the O ring grooves, why not bore and sleeve the bore in the trans.
Lawrie
 
With the Thompson rod what tolerance class does it need? L, N, or S? And I’m guessing the carbon steel should be used rather than stainless.
 
Here is a link to the McMaster-Carr catalog. Notice that these shafts have a "soft" 2" end on them. This makes it a lot easier to machine the hole for the retaining pin at the rear. I used a carbide milling bit in my mill - and made sure that I drilled the hole close to where the case hardening starts, then cut the appropriate amount off the end (the rest of the soft part).

I use a tool-post grinder on my lathe to cut the O-ring grooves into the finished shafts.

https://www.mcmaster.com/products/linear-shafts/shafts-2~/linear-motion-shafts-with-machinable-ends/
 
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