Early Tranny Case vent 34720-36 Thread

Early Tranny Case vent 34720-36 Thread

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10Pin
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Early Tranny Case vent 34720-36 Thread

#1

Post by 10Pin » Thu Nov 07, 2019 2:21 am

Hey All,

Used the wealth of info on this site often, but this is my first post... Can someone advise the thread size for the early transmission case vent 34720-36? I've got a set of 1950 cases that I am cleaning up. This hole is buggered to the extent that none of my "standard" taps or chasers will feed in. Before I force something and make a bad situation worse, I want to make sure it's not some strange thread, like the 1/4-24 screws for the top cover!



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Re: Early Tranny Case vent 34720-36 Thread

#2

Post by Robbo » Thu Nov 07, 2019 3:15 am

I thought it was the same thread as the top cover screws but not 100% certain. It is one of the screws that has no details in the parts manual.
I have a transmisson on my bench at home, if no one has solved this for you beforehand , I will pull the vent screw when I get home and post the details for you. It is only 10am here so it will be a while until I can get to it.

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Re: Early Tranny Case vent 34720-36 Thread

#3

Post by 10Pin » Thu Nov 07, 2019 5:18 am

It's definitely bigger than the 1/4-24 (again, weird thread!) bolts for the top cover. Seems to be 5/16, but I can't tell the thread pitch due to the amount of gunk and buggery... This tranny didn't arrive to me with a vent installed, and none of the other ones around either my garage or my buddy's are the early style. All the other ratchet tops available to check, use the top cover vent screw.
I suppose I could always just tap and plug the case hole and use the later style vent screw, but I just don't like the thought of molesting this otherwise survivor case.

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Re: Early Tranny Case vent 34720-36 Thread

#4

Post by RUBONE » Thu Nov 07, 2019 5:20 am

H-D used 5/16-32 for grease zerks. I suspect it is the same.

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Re: Early Tranny Case vent 34720-36 Thread

#5

Post by 10Pin » Thu Nov 07, 2019 5:55 am

RUBONE, I think you might be right! Looking from the inside of the case, now that I have all the guts out, it does seem to be very fine thread. My thread gauge won't quite fit in the hole, but by eye, it looks very close. I'm going to grab a 5/16-32 tap just in case, and once I get the Colony kit in the mail, I'll know for sure, and proceed accordingly.
Now I'm just hoping I can save this hole without welding it up... :|
Thanks all for the assistance!

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Re: Early Tranny Case vent 34720-36 Thread

#6

Post by Raytag » Thu Nov 07, 2019 8:32 am

I don`t know an answer however from a machining point of view: No fine threads in aluminium. Maybe a thread chaser is a better option

Ray

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Re: Early Tranny Case vent 34720-36 Thread

#7

Post by Robbo » Thu Nov 07, 2019 2:25 pm

I pulled the breather and it is 5/16 28.

I can see why the thread is munted now. I got the breather out easily but I cannot get it back on
Way to fine thread for alloy.

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Re: Early Tranny Case vent 34720-36 Thread

#8

Post by 1950Panhead » Thu Nov 07, 2019 4:23 pm

Used the wealth of info on this site often, but this is my first post... Can someone advise the thread size for the early transmission case vent 34720-36? I've got a set of 1950 cases that I am cleaning up. This hole is buggered to the extent that none of my "standard" taps or chasers will feed in. Before I force something and make a bad situation worse, I want to make sure it's not some strange thread, like the 1/4-24 screws for the top cover!
The vent is 5/16-32 I have the tap

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Re: Early Tranny Case vent 34720-36 Thread

#9

Post by andyinlz » Thu Nov 07, 2019 6:13 pm

If this is actually an early tranny, note that the vent is on the kicker cover.

Or maybe just inside where the kicker cover mounts (too long since I looked at mine).

Anyway, the broader moral to the story is that is is not a vented tranny top screw like the "newer" trannies!

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Re: Early Tranny Case vent 34720-36 Thread

#10

Post by 10Pin » Thu Nov 07, 2019 8:24 pm

andyinlz wrote:
Thu Nov 07, 2019 6:13 pm
If this is actually an early tranny, note that the vent is on the kicker cover.

Or maybe just inside where the kicker cover mounts (too long since I looked at mine).

Anyway, the broader moral to the story is that is is not a vented tranny top screw like the "newer" trannies!
It's definitely on the case, not the kicker cover. But given the wonky threads I have, and the tiny thread pitch, this one might end up tapped bigger and plugged, and vent through a top cover bolt like the "newer" ones. :shock:

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Re: Early Tranny Case vent 34720-36 Thread

#11

Post by Andygears » Thu Nov 07, 2019 11:16 pm

Robbo wrote:
Thu Nov 07, 2019 2:25 pm
I pulled the breather and it is 5/16 28.

I can see why the thread is munted now. I got the breather out easily but I cannot get it back on
Way to fine thread for alloy.
So Robbo, while the breather is out, how bout a picture of it and maybe some measurements? It seems like an oversized thread on a re-creation in a lathe, with a new common thread in the case would fill the hole and be only slightly visible. Maybe 3/8-24 ?

My thoughts,
Andygears

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Re: Early Tranny Case vent 34720-36 Thread

#12

Post by Robbo » Fri Nov 08, 2019 12:45 am

No problems, I can do that. Probably won't be until tomorrow when I have some time and good light.
I will also double check the thread pitch to confirm 28 or 32. I was pretty sure the 28 thread guage fit it but I will check (measure twice cut once).
It is still out as it seems to be a bitch to put back in, fine thread in alloy is eaay to mess up. It only takes a slight burr and things just get steadily worse so I called it quits last night and will go again in bright daylight instead of workshop flouro light.

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Re: Early Tranny Case vent 34720-36 Thread

#13

Post by Robbo » Sat Nov 09, 2019 2:41 pm

1950 Panhead is correct it is 5/16 - 32 thread.
See the pictures below, I hope the details are useful.
Things not covered in the pics
Hex size is 5/16
Breather hole is the same size as a No 6 oxy-acetylene tip cleaner and is drilled right through from one side to the other.
Sorry about the metric measurements, it is what I have.
Image
Resized_Screenshot_20191109-212157_Gallery.jpeg
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Re: Early Tranny Case vent 34720-36 Thread

#14

Post by Robbo » Sun Nov 10, 2019 5:50 am

In pulling the vent scew, I realised that my trans also has the vented top cover screw as well. Will that be ok or is it too much vent?

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Re: Early Tranny Case vent 34720-36 Thread

#15

Post by Bone Head » Sun Nov 10, 2019 1:05 pm

As long as it actually vents it should be ok. I can't grasp any harm from too much venting.

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