1941 Super Coupe Gearbox Question -Mystery Hole

[SuperCoupe8]

Hi Guys,

 

Was going some clean up underneath the 41 Coupe body and noticed oil weep out of this hole.

Ive got no idea what it is or its purpose - Breather?? Bracket?? Manufacturers hole?

 

Can anyone advise as I couldnt find it in the manual

[Bloo]

Is it threaded? I believe the pin that holds the reverse idler shaft goes there. I suggest not driving that until you find out for sure.

 

Here is s similar but not quite the same transmission from a 36 Pontiac. If I remember correctly the "bolt" threaded into the case, but had a "pin" section that stuck out further than the threads locking the reverse idler shaft in place.

 

 

See the hole in this shaft at the upper right of the pic? The part that stuck past the threads engaged that hole.

 

 

 

Edited July 23, 2022 by Bloo (see edit history)

[1939_Buick]

Will look if I have a (Buick) page for the 5 bolt casing - 248ci

Edited July 23, 2022 by 1939_Buick (see edit history)

[buick looks fine for 39]

yep it's the pilot hole for the reverse idler shaft retaining pin.

                                                         

                                                               Thanks 

                                                                Leif

[EmTee]

Now, need to find a pin...

[NailheadBob]

Page 107-A in above photo (A-G is Lock, group 4.435) part # 590832 , is on ebay:  https://www.ebay.com/itm/334068043429?epid=658280553&hash=item4dc801cea5:g:Sx4AAOSw9Ohg5gid

 

Bob

EDIT: here is photo of paragraph from service manual.

 

Edited July 23, 2022 by NailheadBob
Add photo (see edit history)

[neil morse]

I will have to check with the Don Micheletti, who supervised the rebuild of the transmission on my Super, but I can tell you that there is no missing bolt (as in the Pontiac transmission shown by Bloo).  Here's a shot of mine after we put the transmission back on the car.  It does not leak any fluid from that hole.

 

[EmTee]

Ah, so the Buick just has a pin driven into the hole?  So, maybe there's no leak there at all.  Could oil from above just be leaking down in and around the hole, making it look like it's coming from the hole?  Clean the oil off the case and rinse-out that hole with brake cleaner or other degreaser.  Then drive and check for leaks (lather, rinse & repeat).

[Bloo]

I can't imagine with the pin being grooved like that what would keep the oil in. There must be more to the story.

 

[DonMicheletti]

The seal of that pin is no different than that of the cluster gear counter shaft. The tight fit can seal it.

But who uses a new pin as the manual says?   No one. The groves only extend part way on the pin at the outer end.

So re-using the old pin usually requires sealant.

I had an Oldsmobile with the same setup and it had no leaks.

 

When we rebuilt Neils trans, I didn't want to remove the reverse Idler just to avoid that possible leak.

[buick looks fine for 39]

There's a difference between an oil leak and oil weeping. Outside of asthetics weeping oil is no big deal and old Buicks normally leak somewhere. Leaking oil is another matter and needs to be addressed. My advice is check the oil level in the transmission case and if it's normal no sweat. Also for piece of mind use a nail in the pilot hole and see how far the nail goes in. That way you can determine if the pin is in place. Then you can plug the hole with a cork or goo if the oil is annoying and remedy the weep if and when the transmission is rebuilt. In old cars there is always something, and it's hard to draw the line on where to stop correcting defects. The main thing is if it runs well and has not major mechanical issues that need to be addressed, drive it and enjoy it.  

                                                                                                                             Thanks

                                                                                                                                Leif

[buick looks fine for 39]

Also judging from the oil wash from the initial picture there appears to be an oil leak  in front ( engine side) of the pilot hole.

[SuperCoupe8]

Thanks to all of you . Looks like it's the pilot hole . I cleaned it out and upon inspection there's no thread. My gearbox sounds great in all fwd and reverse gears . I cleaned all the residue oils that where due to old leaking rocker cover gasket. I've seal the hole and good to go ..once again thanks to all ..appreciate it

[SuperCoupe8]

21 hours ago, DonMicheletti said:

The seal of that pin is no different than that of the cluster gear counter shaft. The tight fit can seal it.

But who uses a new pin as the manual says?   No one. The groves only extend part way on the pin at the outer end.

So re-using the old pin usually requires sealant.

I had an Oldsmobile with the same setup and it had no leaks.

 

When we rebuilt Neils trans, I didn't want to remove the reverse Idler just to avoid that possible leak.

That's what I think it is

[Janousek]

I've done a couple of those transmissions and bob's automobila has new pins.  Nice to know it's in there so the shaft can't rotate in the housing.  Chances are slim it ever does.   I usually drill,tap, and slide hammer the old pins out.    If Bob's doesn't then Mcmaster carr will have tapered pins by measurement.