Does anyone no what the purpose of this hole is? There is fluid leaking out of it. I looked at another th350 that my dad had laying around and there appears to be maybe a metal plug in the same location.
The tranny is a th350 in my 1973 k5 blazer. I just got my blazer back from the tranny shop, where they rebuilt my transmission. When I got my blazer home, I noticed a bolt sticking awkwardly out of the hole and there was atf leaking beneath it, the “bolt” came right out when I went to inspect it. It continued to leak fluid when I took it on a short drive.
I’ve searched online and looked at every diagram I could find but wasn’t able to find any information on this hole/port?? Does it just need to be plugged??
Thanks

 

I would say that it is an access hole for internal port machining that should have a pipe plug in it. From the looks of the plug you have, it would seem that someone forgot to install it prior to putting the governor back in and decided to modify it to the point of uselessness rather than pull the govenor cover back off. Hopefully they did not mess up the threads in the case... If they did, it looks like there is enough meat on the case to allow you to tap the 1/4" pipe thread hole a bit deeper to allow a new plug to be installed and sealed up with some teflon tape and/or liquid pipe sealant. Since you need to get a new plug anyway, I would recommend one with either an external square head or an internal hex rather than the external hex as you currently have. Reason being, if you have to tap the hole out, the external hex head pipe plug might not allow the threads to seat properly before the hex hits the mouth of the hole. The external square head and internal hex allow for the plug to bury deeper into the hole.

I just happen to have a TH350 that came out of my '70 Chevelle sitting on the floor of my shop right now so it should have the same port that I can see what is in there tomorrow when I get to work.

 

Thanks swartlkk for the reply and info! I’m curious if there is a plug or bolt on your Chevelle’s TH350. If you don’t mind letting my know what you find out that would be great

I tried to thread in a new bolt yesterday, but after fighting with it for a ridiculous amount of time (the bolt would just spin) I got a mirror and flashlight and it looks like there’s no threading in the hole at all?? So I wonder if it originally had a metal plug (like the second photo)?






The other th350 with a metal plug

 

The metal plug would likely be the factory method of sealing off a machining access port. Maybe something like this soft plug --> .378" Steel Cup Plug - transmissionpartsusa.com? You would need to get an accurate measurement of the hole size to get the correct soft plug.

I didn't know if someone removed the plug at some point and tapped the hole which is also an option as long as you are careful not to crack the case installing the pipe plug.

 

Thanks swartlkk. I think I’ll give the soft plug a try and keep an eye on it to make sure it doesn’t leak. If it does, then I’ll have to tap the hole and go that route. Thanks again for the detailed info and recommendations!

 

In looking for more information on this I stumbled onto the Melling Expansion/Freeze Plug Guide (PDF Download) that should give you a wide array of options if you find that the hole in your case is different than what is referenced in the link I previously provided. You would be looking for a deep cup plug.

Also worth noting is the staking that is shown on the picture you provided showing this plug. Staking is used to retain the plug beyond the friction fit to the bore it is set into. Basically you use a punch to upset the material into the bore after the plug has been set in place. Staking is not a cure to a leaking plug, rather a backup to keeping the plug in place.

 

Thanks for the link to the Melling catalog! I stuck a rubber plug in the hole so that I could drive it to the tranny shop this morning. The technician offered to put in a new plug or that he could tap the hole for a bolt. I wanted to try with the plug first. The local parts guy had a 3/8” soft plug that I bought and brought back to the tranny shop (they didn’t have any plugs on hand). If that size isn’t correct then I will have to order one. I’m scheduled for Wednesday morning to have them install it.
I will update how it turns out

 

Just wanted to update: I got my blazer back from the transmission shop. They installed the soft plug. I will keep an eye on it for any leaks, but crossing my fingers it should be good to go!



Picture of new soft plug installed

 

Looks like the proper repair. Thanks for reporting back with the fix and let us know if it leaks. I would hope that the shop would have used some Loctite 540 (retaining compound / core plug sealant) to prevent leaks and help hold the plug in place.

 

I hope that they properly installed it also! I usually do all of the work on my blazer myself but in this case, because they had just rebuilt it, I was advised by a family member to have them do it since it is under warranty. I will update if it has any issues. Thanks again swartlkk for your expertise and recommendations!