I just changed motors a few weeks ago. Now on what was a dry transmission for months is leaking out the front seal like crazy. I had fixed the leaking output seals and speedo seal.

Could a plugged transmission vent cause it the seal to blow out? I drove it around on the old motor maybe only 15 miles. On the new motor it started leaking fairly quick. I was winding it out to about 6000-7000 rpm, will that cause more pressure in the transmission case?
I pulled the vent and could not see much in it. I cleaned it out with brake cleaner, should there be valve or something in it? Or is it more likely the input shaft moved around enough mating back to the clutch that the decades old seal gave out?

It’s just an open vent (no valve) but it does have to be facing the right direction or air pressure will suck the oil out. A common thing to forget on 915 trans conversions.

Also make sure it’s filled the correct amount. Car needs to be level when you check.

Also, To run a 915, you have to flip the ring and pinion gear to the other side. So the vent is on the wrong side, and the spinning ring gear will push gear oil out the vent.

You have to move it diagonally to the other side of the case. Redrill the hole, and plug the original.

Now don't I look stupid. I just remembered that applies to a 901, not a 915. The 915 vent is on the center rib, and won't be affected by ring gear placement. But it does need to be turned 180 degrees to match the direction of travel.

Clay

It is a 901, if I understand correctly the vent hole is facing forward. Which is the direction it was, and the direction I put it back.

My 915 has the stock breather and per the Manuel, I pointed it 45 degrees to the right facing the passenger side, just like the previous 914 trans. I have no oil coming out of the breather. That includes a 9 hour drive to the Petaluma WCR and other events.
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Random question: did the the engine you just installed have a pilot bearing in the flywheel? I had a problem once with a flywheel that did not have a pilot bearing. The input shaft from the trans had a noticeable leak despite having a brand new seal.

Yes, new pilot bearing. I ordered new seals tonight. One plus a spare, in case I screw up the first one. Since I have to take it apart I am replacing the throw out bearing too. Which I reused, I tried to force some new grease into it before using it. It didn't make noise and still doesn't. I'm sure there is some nice Arizona dirt in it though.