O-rings on transmission countershaft

40cpe

40cpe

Well-known member
I remember a thread a good while ago about how to make the grooves for the o-rings and what size o-ring to use. I can't find the thread. Does anyone know the particulars on how to do this? I have access to a machinist, but feel I must be able to tell him something to start.

I'm rebuilding a 78 case and the shafts push through easily with my fingers. They have always leaked. Solving that mess would be a great improvement.
 
The guys around here have grooves cut in the case inboard of the lock pin in both bores at the rear of the case and the one in the front. I have 3 transmissions that are O ringed and they don't leak a drop. I don't know the size of the groove or the o ring but the machinist who does the work would figure that out.
Some people groove the shaft but I don't like that idea.
 
If you have access to a machinist ,ask him about doing this
I set up the empty case on my mill,bore to holes for the cluster shaft 3mm oversize,while its still set up on the mill,turn up the new bush from steel, with the interference and about .010 under on the bore,using a bolt and nut and loctite super retaining compound, pull it into place,then bore it to the correct size.no drama,I have done 3 or four of my cases like this and they work fine.
Lawrie
 
Parker o-rings come in all sorts of different diameters of stock cross sectional thickness and different ODs. A person has to size the shaft or bore and decide on a depth/width of cut that will correspond with the closest cross sectional o-ring size and either the OD of the shaft or the ID of the bore. If you use an o-ring size that is too big, it won't go in easy and may shear the o-ring. I usually set the width of cut right on the money but leave the depth just shallow enough for the o-ring to protrude just a very small amount. It doesn't take much to get a good seal.

Rather than go through all that trouble, I usually put some RTV sealant on the protruding end of the shaft and in the receiving bore on the other side just before I shove it in . I then push the excess around the bore line a bit before wiping it off. I haven't had a leak yet but then again I've never had an old vehicle that didn't mark its spot somewhere. I sure don't lose any sleep over it.
 
rotorwrench, are you saying that you 0-ring the shaft AND use the RTV sealant? Or have you had success with just the sealant?
 
rotorwrench said:
parker o-rings come in all sorts of different diameters of stock cross sectional thickness and different ods. A person has to size the shaft or bore and decide on a depth/width of cut that will correspond with the closest cross sectional o-ring size and either the od of the shaft or the id of the bore. If you use an o-ring size that is too big, it won't go in easy and may shear the o-ring. I usually set the width of cut right on the money but leave the depth just shallow enough for the o-ring to protrude just a very small amount. It doesn't take much to get a good seal.

Rather than go through all that trouble, i usually put some rtv sealant on the protruding end of the shaft and in the receiving bore on the other side just before i shove it in . I then push the excess around the bore line a bit before wiping it off. I haven't had a leak yet but then again i've never had an old vehicle that didn't mark its spot somewhere. I sure don't lose any sleep over it.
Click to expand...
xx2
 
lots of after market shafts are undersize.mac has the correct size shafts that properly fit the case provided the case holes are not oversize.
 
Bringing this one back up, as I have a project in the works that I don't want to leak like my current car does (lots).

I understand the comments above about cutting the groove in the case and keeping the shaft untouched.

But, somewhere I read about using a plug in a counterbore on the front of the trans, shortening the shaft just a little. Anyone have real experience with this? Would the shortened shaft reduce strength much? Promote more cracking in an already weak area?

And, anyone in the O-ring camp have any sizes or part numbers that have worked good for them?
 
I saw a video on Ytube a couple weeks ago. This person recommended to chamfer the holes in the 3 outer ends of the case and use rtv sealant in the void created. He said it has worked well for him.
 
it was rumbleseat who told of counterboring the front of the case about 1/8" deep about 1" dia, shortening up the shaft a similar amount, and after installation of the shaft, fitting a lens type freeze plug into the counterbore to seal leaks outta the front of trans. I have previously done that and it works great!. The original shafts, as supplied by Ford, were actually an interference fit in the back of the case, this prevented any leakage in that area. modern repop shafts are undersized amongst other issues.
 
3M black weather strip adhesive works for me. Have used it for years with no leaks. Coat front of housing bore and rear of both shafts just before last inch is installed. Push home now fill pin cavity with the 3 M Push pin home blocking end of hole with finger to force adhesive in crevices. Safety wire pin and now coat both ends of pins and ends of shafts at housing. Let it dry before adding oil. No leaks happening here.
 
For sure the best way is to "O ring " the case. One of our local club members came up with the idea and actually made a portable tool that bolted to the case. I set mine up on a milling machine and used a boring head with the cutter I made. I did about 5 of these for other club members. The best part is that you can use a modern transmission oil like MT-90 by redline. Shifts super smooth and absolutely no leaks.
I have a case already done, Pm if interested.
 

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The "O" ring size is 3/4" id to fit the counter shafts and if I remember correctly they are 3/32 cross section. Your machinist can look up an "O" ring grove specification for the specified "O" ring. Just be careful to avoid the tang on front and the lock pin holes on the back.
 
Also you will need to put a taper on the end of the two shafts, so they will push in with out damaging the "O" rings.
 
40coe said:
For sure the best way is to "O ring " the case. One of our local club members came up with the idea and actually made a portable tool that bolted to the case. I set mine up on a milling machine and used a boring head with the cutter I made. I did about 5 of these for other club members. The best part is that you can use a modern transmission oil like MT-90 by redline. Shifts super smooth and absolutely no leaks.
I have a case already done, Pm if interested.
Click to expand...
545085


545086
 
alchemy said:
Bringing this one back up, as I have a project in the works that I don't want to leak like my current car does (lots).

I understand the comments above about cutting the groove in the case and keeping the shaft untouched.

But, somewhere I read about using a plug in a counterbore on the front of the trans, shortening the shaft just a little. Anyone have real experience with this? Would the shortened shaft reduce strength much? Promote more cracking in an already weak area?

And, anyone in the O-ring camp have any sizes or part numbers that have worked good for them?
Click to expand...

I’ve done that many times. Take just enough off the front side of the shaft then install a 3/4” plug like goes in the pan rail of the block with a dab of RTV.
 
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