Input shaft seal Problem with 915 Mag case

[tom1394racing]

I dropped my 1973.5 915 gearbox off tonight with the CT gearbox rebuilder. He took one look at the input shaft and informed me that my case had the dreaded input shaft seal reject configuration.

He has seen multiple problems with racing 915 gearboxes that he has rebuilt with this configuration. The problem is that the input shaft seal either leaks or becomes dislodged from the case. He advised that I have my gearbox rebuilt with a '74 style mag case which he has on hand that is not suspetible to this problem. I committed to an exrtra $300 for the rebuild with the '74 style case.

Has anyone ever experiecnced this same problem?

[Jim Richards]

Uhh yes, twice now.

Gary Fairbanks (the rebuilder mentioned above) told me he wouldn't replace that seal for me because he couldn't gaurantee that it wouldn't leak. Imagine my disappointment (but not surprise) when I had another shop do it and, 18 months later, it leaks. And for an added bonus, my 18 month old clutch disc has absorbed Swepco 201.

[Grady Clay]

Guys,

Stand by and I will offer a possible solution we did many years ago. Right now I need some sleep for our games tomorrow.

Best,
Grady

[Oldporsche]

My guess is that Grady has a fix for this problem. Isn't this the case where the seal goes in from the inside?

David Duffield

[klaucke]

The suspense is hard, I eagerly await another tidbit from Grady's sea of knowledge.

How is the 74 mag case different? All I knew of was a difference in gear ratios.

[Jim Sims]

I believe this leads to Grady's fix:

72 Clutch Replacement/Leaky Flywheel Seal..

[Jim Richards]

I read up on Grady's fix and it looks like a great approach to keep leaking tranny oil from getting back to the clutch disk. I would really like to know what to buy for this "dam seal" and where to source it.

Grady, any recommendations / details that you can provide? Thanks!

[tom1394racing]

It seems like Grady's fix will not prevent the leakage but only keep the leaking gearbox lube from ruining the clutch. I would guess that you'd still have a mess on the bottom of the gearbox and on the gargage floor. Am I missing something?

[Grady Clay]

Sorry for the delay, I was too tired last night to properly respond.

I don’t know how this inside seal passed the engineering
“Laugh Test” when originally designed.

Yes, the absolute best solution is to replace the main differential casting
with a later one using the “install from the outside” input shaft seal.
However this requires resetting the differential side bearing
pre-load, checking the pinion position and setting the
ring-to-pinion backlash and contact patern.
Not inexpensive but very worthwhile.
At the same time you should replace the differential side
cover with the later reinforced version.
Yes, I have seen some changed without the major effort
to do with the R&P.
I think these are the transmissions that have pinion failures.

The “dam seal” is simply a measure to prevent transmission
lube from getting on the clutch when an input shaft
seal (whatever kind) fails.
It is much better to discover some oil on the garage floor
than have the clutch insidiously not releasing and
trash the syncros and other parts.
The “dam seal” is not a fix for a leaking input shaft seal.
We devised this when we first saw the “install from the
inside” input shaft seal.
At the time there wasn’t any alternative to the original seal
and clearly a failure leads to a ruined oiled clutch disc
and possible shifting damage.
The “dam seal” is applicable to all transmissions;
356 thru late 911s.

Here is one of the seals (I don’t remember which transmission
it fits) and our homemade installation tool.
The important issues for the installation are first, the seal
must be far enough inside the guide tube so there isn’t
any possibility of the clutch disc hub touching it.
The other is to have the seal square in the bore of the guide
tube so it stays in place.
We always installed it with some sealant as glue.







These seals are available from any commercial seal supply house.
They are very inexpensive.


EDIT addition:

The big issue is you can’t just drill a drain hole, the dam seal
is absolutely necessary if you drill a drain hole.
The reason is that when the engine is running, the
clutch components act like a centrifugal fan.
This makes low atmospheric pressure at the clutch disc hub
and in the clutch release bearing guide tube.
Air will tend to come in the drain hole and go towards the
clutch hub, forcing any oil with it.
The dam seal prevents the oil from going that direction.

The dam seal does not touch the input shaft.

When installing the dam seal do not put in too far.
The input shaft has a ground surface for the input shaft seal.
The dam seal must be slightly towards the clutch from the
end of the ground surface.
This prevents a drop from getting past the dam seal.

The above homemade tool is hollow to fit over an input shaft.

We made it standard practice to install this mod on every car possible.
I’m sure we saved many owners from unnecessarily expensive repairs.
Yesterday Pelican Bill was at our BBII lunch. After inspection, he thinks he has a ’73 transmission with the Rennenhaus “dam seal” from probably 20+ years ago - no oil on clutch.


As a reminder when installing input shaft seals; always inspect the input shaft sealing surface for wear or damage. It is best to have the lip seal on a fresh part of the ground surface towards the transmission.


Best,
Grady

[wevoid]

Tom,

We have an upgrade process available that modifies the 1972 final drive housing.
The end result is a new removable guide tube that has the SC style input shaft seal installed in it.
This upgrade allows the guide tube to be removed without disassembling the transmission - for future seal changes.
Cost is $298 and this not only gives a new guide tube, but eliminates the costs of CWP set-up that is necessary with a replacement case.

Regards

Hayden

[Grady Clay]

Hayden,

Cool. Technology progresses. I am glad to see another solution to this stupid problem. Good for you.

Best,
Grady

[bkdamkr]

Hi Hayden.
I need the mod. I just discovered that the input shaft seal on my 73 911 is leaking. Please contact me at opienzip@direcway.com, so that we can get connected for me to the mod done.
Thanks,
Brian

[bkdamkr]

And Grady, as a fallback, can you give me a source and model number/description for the dam seal, or is in the link?
Thanks,
Brian

[Grady Clay]

Brian,

Hayden’s mod sounds like a good choice.

I went on CR Industries site and couldn’t find this seal P/N. This week I’ll try and go by Rocket Seal (one of our local big deal industrial suppliers) where this seal came from and see if they can cross reference this CR 8620.

Hayden,
You might consider adding the dam seal to your mod. The advantage is that when the input shaft seal fails (and they all do sooner or later) the transmission oil doesn’t contaminate the clutch.

Do you make a new guide tube or mod an SC one?

One thing I have considered, but never tried, is a drain tube from the guide to the outside and not on-center. A length of ¼” Polyflow would fit and is sufficiently robust to outlast any seal. I thought about adding a cotton thread in the drain tube to wick any oil and restrict the counter-flow air.

For everyone:
The critical issue is to use a NEWLY MANUFACTURED input shaft seal that is fully compliant, not one that has been sitting on a shelf for 20+ years. Lip seals have a definite shelf life. Pay attention to who the manufacturer is. Lip seals that fit are manufactured all around the world – I don’t think they are all suitable for our application.

Best,
Grady

[goggles]

.

[wevoid]

Brian,

I will email you. As you are local SF Bay Area, perhaps you can come by and have a look.

Grady,

We make a new guide tube from scratch, so it would be possible to put a "dam" feature in the turning, but at this stage we were content with solving the common issue.

I will post some pics of the modified parts.

Regards

Hayden

[bkdamkr]

Thanks, Hayden.
I'll watch for your email. I've got to do something before I put the eng/trans back in. I need a new front case because I broke off the boss that the spedo cable screws onto - I think that Parts Heaven will have one for me early next week. I'd love to get the input shaft seal sorted out next week as well.
Brian

[wevoid]

Here are some images that show the nature of the upgrade

Firstly, a stock 1972 / early 1973 guide tube - fully integrated into the casting.

[wevoid]

Secondly.....

System will not allow me to upload another of the pics over 100Kb.... so I will edit this with images at a later date.

Regards

Hayden

[Jim Richards]

Grady, here's the info about the CR 8620 seal that you referred to in your solution to this problem.

http://www.chicago-rawhide.com/catalogs/457010/sealdetail.asp?s=8620



Do you have more info about the insertion tool you used? It would be nice if we can recreate it.