Sealing the 915 - T/O Bearing Tube

cab83_750 · 11-18-2006, 10:34 AM

I have completed my 1st 915 rebuild :

:

!!!

So far no leaks with fluid in it. One thing I am unsure is the throw-out bearing guide tube. I bought a brand new o-ring, lubricated the o-ring with regular engine oil, oil around the surfaces also, and inserted the tube into the housing.

Instead of just using oil, should I have used other 'sealing' agent to ensure long-term leak-free miles? I am dropping the engine today.

As always, thank you.

Windsor

cab83_750 · 11-18-2006, 04:49 PM

Anyone? Bueller? Bueller?

dentist90 · dentist90's Garage

No, just tranny oil. The seal around the input shaft depends on rubber contact against the shaft. You wouldn't want to risk getting some silicone goop on the 'mating' surfaces and having a poor seal. The thing about O-rings and rubber seals is that they are designed to allow movement while maintaining a seal. Nicks and tears and the inevitable hardening of the rubber itself is what causes leaks. They do have a limited lifespan.
I assume that you put the engine and tranny back in some time ago and you're doing the engine drop now for something else? Check the bell housing and flywheel for oil spray from this seal leaking.

Grady Clay · 11-18-2006, 07:00 PM

VERY IMPORTANT

Search on “dam seal”, other 915 issues and my name.

This was developed for the ’72-> inside 915 input shaft seal but is applicable for every Porsche transmission.

Best,
Grady

cab83_750 · 11-18-2006, 08:36 PM

Dang Grady, all I was inquiring about was the O-ring; now you have me worried about some ***** Dam Seal

Just kidding....I actually appreciated the input and will be installing the dam seal and the groove.

Will I destroy my O-ring and my shaft seals if I were to pull out the guide tube?

Thanks.

Walt Fricke · 11-19-2006, 12:30 AM

Why are you planning to mess with any of this? You haven't mentioned having a tranny fluid leak. Got the "what did I forget" jitters? I don't think that O ring is a high failure/leak area. None of my boxes have shown leaking there.

I've never done anything to the O ring (in fact, I have reused them, though it's always good to replace such things). But I don't think a little lubricant would harm anything either. It certainly should not be necessary to use any sealant.

Getting the seal to be square inside the tube is valuable (if a seal is at an angle is sort of acts like a sweeper to any dust particles that come its way, which pushes them against the seal lip much harder than if the lip was always just touching the exact same very thin circumferential line). And it seems wierd to me that Porsche did not machine a lip to catch the seal and hold it in exactly the right place. But it isn't hard to get it there and square.

But I bet you naturally thought to put a little lubricant of some sort on the shaft before the seal passed over the splines on the way to its new home. It would be nice to have a thin smooth sleeve to keep the splines away from the seal lip when installing things, but I have gotten away without one when I have been messing with my trannies.

Walt Fricke