I have had the drivetrain back in my 69 for about a month now. I haven't had any leaks. Then tonight on my garage floor is probably six ounces of tranny fluid. So I crawl under the car with a light, and see that the fluid is running from out of the driveshaft.

It is leaking where the front u-joint is. Not around the tailshaft seal. But out the end of the splined part of the driveshaft itself. Right in front of the U joint, in the center of the recessed area.

What can I do to fix this?

It depends on whether it's a hole or a crack.. It could be warning you of an imminent failure..
If not, you could use sealant, but I doubt it would adhere very well for any period of time.
Welding is a no-no on a forged part like that, -unless you have it crack tested, stress relieved, heat treated and possibly machined after the welding. (ever seen a slip yolk fail? It makes quite a mess.)
I'd just replace it if it were me.

Some slip yokes have a hole in the rear center as a vent. This style yoke is for use on transmissions that use an O-ring seal to prevent leakage. Can either plug the hole or use a yoke w/o a vent hole.

Bob.

I haven't pulled the driveshaft yet, because I've been so busy. But it has been in the car for over a year and didn't leak. Then I cleaned it up and painted it, installed new u-joints and re-installed it. It still didn't leak, then it sits in my garage for a month or so and starts pouring.

I haven't even driven it yet. I'll take it out and see where it's coming from, thanks everyone for all the advice

I pulled the driveshaft and seperated the front yoke. The fluid is coming from the vent hole in the center of the yoke. It is about a 1/16 hole.
What should I do to stop this leak?

I thought about taking my mig and in about two seconds I could seal up the hole. But I don't want to do this if it will create more problems.

Personally, I'd MIG it and forget it.

But if you're worried about somehow damaging the part by welding it, you could drill, tap and insert a short bolt with thread sealant.

You could clean it well and put a blob of JB weld on it. (epoxy from hell)

You could get a used one at a boneyard for a few bucks, or a brand new one for quite a few more.

But I'd MIG it.

I used the JB weld on the '67, it's held up for over a year now.

I pulled the driveshaft and seperated the front yoke. The fluid is coming from the vent hole in the center of the yoke. It is about a 1/16 hole.
What should I do to stop this leak?

I thought about taking my mig and in about two seconds I could seal up the hole. But I don't want to do this if it will create more problems. Using the MIG is the correct response to this issue. The hole doesn't belong there for our 1st gens <G>.

Bob.

So you think this yoke has been changed before? And the original didn't have a hole? I'm just curious why it took so long for it to start leaking.

Or instead of migging it, there is a plug made specifically for this problem. Go to (call?) your local transmission rebuilder and he should have the plugs that are made to press down into the yoke to seal it up. If you install the plug, it won't leak anymore, and for some strange reason should you decide you need to remove it later-you can!

The plug should cost you less than a $1, and once in your hand you will see how easy it is to install. It is thin sheet metal, with legs, and a rubber plug in the center. The "legs" help hold it in place once you press it down into the yoke. The other good news is that you don't have to take the yoke apart from the driveshaft. Fast, & simple, what more can you ask for?

If anybody needs one of these, drop me an e-mail, and I can get you one for the cost of postage.