well tomorrow is my Firebird's first birthday and I'm so close to firing up the engine I can taste it. Last night I finished up the exhaust enough to start the engine and started putting in fluids. Got a few leaks but only one is concerning me right now. One was through the vent tube on the TH400 which I believe tells me that I cannot fully fill it without it spinning. Second leak was heater core which angers me because it was a new part but I bypassed it so whatever I deal with it later.

A little history. Got the car a year ago; it's a 67 coupe. Car originally was a 326 with 2 speed trans. I put in a 400 engine. Car had a TH400 in it when I got it. It also had the yolk, driveshaft, rear end in it and this all seems to fit up just fine.

So my third leak is transmission fluid leaking out of a hole in the middle of the yolk. Not sure I can describe this very well but the yolk gets inserted into the back of the transmission. It mates up with the spline in the transmission output shaft and there's an oil seal contacting the outer diameter of the yolk. There's transmission fluid dripping out through a hole in the middle of the yolk. Like fluid must be seeping past the splines and then through this hole. Why would there be a hole and should I just plug it? I can't get a great look at it because the U-joint is in my way. Perhaps that yolk is a bolt on type? I don't remember my transmission output shaft have a thread for a bolt. Once I get home from work I'll pull the driveshaft out and check things over. If I can get this plugged and find some spark plug wires then tonight I'll attempt to fire this thing up.


any ideas?


Dan

Yes, the transmission can't receive its full allotment of fluid without being run. Usually you should start with about five quarts of tranny fluid after a complete rebuild and keep filling as needed. The yoke should seal as you suspect.

Dan, I have been dealing with yoke issues with mine to. There is a hole in the yoke so it can breath because there is an oring seal inside on the output shaft. Your yoke should be about 7 1/2 inches long from the center of the ujoint. If it`s only 5 1/2 your yoke will not extend to that oring and then it will not seal. No matter which one you have you can just seal that hole with JB weld then if it still leaks it probly getting past the press plug in the end, there again clean it up and put some JB weld on it or get a new yoke without a breather hole.

It would be much better to get a drive shaft that extends all the way in to where it was designed to fit. You could cause problems with you trans if the drive shaft isn't in all the way.

Dogface I believe you're hitting the nail on the head here. I pulled out my driveshaft last night and the hole is tiny, like a breather hole. My yolk also looks as if someone cut it short about 1/2 inch after the spline stops. I JB welded it last night then once I get home from work tonight I'll pop it in there, prime the oil pump, then see if this engine will fire up. Keep your fingers crossed for me.

Jim I'll have to look into finding a different yolk that extends in further but for now this one will do just fine. My car won't be moving for many months so that driveshaft is really just a plug on the end of the transmission right now. My yolk does cover all of the spline but stops shortly after that.

thanks guys

One thing to think about; That hole is probably there so that when your driveshaft moves in and out when your suspension travels the compression pressure gets relieved. I can imagine there can be quite a bit of pressure and suction when it moves back and forth on the spline. This could really put some pressure on your tail shaft.

Sounds like a 1 ton truck yoke. Thier shorter with a hole.
Car th400's didnt have holes. At least any i've seen.

could certainly be a truck yolk. This car had many weird things in it when I bought it and the TH400 is not stock

my yolk has definitely been cut short by someone at home though. Was cut with a drop saw or band saw and cleaned up with a grinder/sander.

They aren't very expensive $27 LINK http://cgi.ebay.com/ebaymotors/Tran...itemZ130102238142QQrdZ1QQsspagenameZWDVW

yolks are cheap and found at any driveline shop for next to nothing. sounds like someone put the wrong driveshaft in it when they converted it to a 400 trans. switch the yolk and it should take care of it. also the jb weld should only be considered a temporary fix as i dont think it would be wise to use for a long term.

Lasy year when i needed a th400 shaft built, no one had one.
Took 2-3 days. Cost $38...arrrh!

yeah the JB is not meant to be permanent. Just enough of a fix to allow me to plug the transmission and run my engine in neutral

Not permanent?
I better not tell the story about using it on a cracked piston pin ring land so i could race one weekend

Glued a weight on a flexplate for a Chevy 400 with JB. Sold the car it was on. Worked on it ten years later and the weight was still in place.