915 Transmission Nightmare

[Adidas]

I'm sure I'm not the only damn stupid idiot that didn't know that the the entire 915 trans has to come apart to replace the little cheap imput shaft seal. Of course I didn't know this and thought the release bearing guide tube was removable like in later 915 units so it could be replaced from the outside. Replaced the other outer seals and took a chance and let this one go and now the trans is leaking oil from here like the Exxon Valdez. No other options right? I gues I'm going to eat a big slice of humble pie.

[Jon B]

If your 915 transmission is a '72 model, the seal cannot be replaced from the outside. If you have a '73 model, post the transmission serial number- even if the guide tube isn't removable, later '73 through '75 seals can be replaced with special tools from the outside.

[Jon B]

Porsche tool P386 is needed to remove input seals from 915 transmissions with fixed guide tubes, from mid '73 through '75 models...

[E Sully]

I am curious about my tranny. It's number is 915/02 7731324
Thanks,
Ed

[Porsche84]

Jon

I'm wondering if you could make a tool to push the old seal into the tranny Diff area. Then pull the side cover and lift out the diff, then cut off the old seal. Then install the new seal from the front without removing the input shaft (on the 73-74 type). Removing the diff is easy.

I just replaced a seal on a 74, but thought it was the same as the 72. Thanks for that tip!

[Grady Clay]

Announcing the then-new 915 in 1971, Porsche curtly noted:

“The driveshaft oil seal is installed so that the lip points toward the bell housing.
The oil seal cannot be replaced from the outside.”



© 1971 Dr. ing. h.c.F. Porsche A.G.


Here I have highlighted the seal in red and the seal-spring in green.





IMHO, this does not pass the ‘engineering laugh test’.
What were they thinking?
Did someone decide this would save a manufacturing machining step?
Was there no oversight?

The good news is the seal was changed during the 1973 production to the system Jon notes above.

915/02 – from 7337375.
915/12 – from 7230507.
915/08 – from 7830838.
Special transmissions – from 7931031.


© 1973 Dr. ing. h.c.F. Porsche A.G.


There are several vendors (WEVO and others) that can modify the ’72-’73 castings to accept an ‘outside-install’ input shaft seal.


Starting with the 1976 model, the seal was changed to be inside a separate clutch release (TO) bearing guide tube.
This system is carried through the 911SC and 911Carrera.


© 1976 Dr. ing. h.c.F. Porsche A.G.



© 1976 Dr. ing. h.c.F. Porsche A.G.

The change in guide tube and seal occurred with the change to the electronic speedometer.


Given Porsche’s great engineering prowess, I don’t understand their difficulty with the input shaft seal.
Even the late system added an O-ring around the guide tube.
That just added another place for a leak to occur and another part to the transmission.
The guide tube must be a more precision and expensive part.
What is wrong with the nice, old VW system used on the 356 and 901/911/914 and others?

Best,
Grady

[Donnsny]

On my race car I had this seal work out of the housing. This really caused a mess. I had installed the seal with hylomar and I am not sure if it wouldnt have been better dry. I think it was aggravated by some high trans temps at the time. I ended up making a retainer, drilled and tapped the inside of the case and screwed and safety wired the retainer to positively hold the seal in place. No problems since. So if is really puking oil out it could be the seal has migrated out of the bore in the case. I really dont see a way you could fix this without taking the trans apart.
Donn

[Porsche84]

Grady

Thanks for all the info, great resource. I'm facing replacing a seal in a 72, so no question about that one. Is 72 the only year the seal is in facing toward the bellhousing? That seems counter intuitive. I always assume the lip faces the liquid you are sealing. I guess Porsche knows best.......

[Grady Clay]

Originally Posted by Porsche84

Is 72 the only year the seal is in facing toward the bellhousing? That seems counter intuitive. I always assume the lip faces the liquid you are sealing. I guess Porsche knows best.......

No, this seal is used for all ‘1972 915s and the 1973 915s through the transmission numbers:

915/02 – to 7337374.
915/12 – to 7230506.
915/08 – to 7830837.
Special transmissions – to 7931030.

I agree, it is counterintuitive and counter to good engineering practice.


Donn brings up a good point.
The seal is not captive, it can slide out to the inside of the transmission.
I have seen this. What a mess.

What is really crazy is the ‘fix’ (’73-’75) and the ‘improved’ seal (’76-’89) can also slide out (although I have never seen one do this).
The original (VW, 356, 901) design was captive.

With the ‘inside seal’, there isn’t any way to replace it without removing the input shaft.
There isn’t a ‘split-seal’ like this.

Donn, on my racer I also safety wire all the other seals (axle flange, etc.) so they can’t come out in the ‘heat’ of racing. I have seen that.

Best,
Grady

[RoninLB]

My 1977 input seal slid inside after 100 miles of driving after a full pro rebuild from a guy out in the NW US to deal with me installing a 250hp/3.4

This was the first time the pro ever seen this happen in his long history. I forgot exactly what syn lube he used for the seal install but after a couple of phone calls he suggested just using dino oil of any weight to re-install. I installed a new seal with 10w dino oil. All has been well for the past 15k miles.

[Jon B]

Jerry's idea about pushing the old seal (on late '73-'75 models) into the diff area, then pulling the diff to remove it, will work as an alternative to the Porsche tool. Find an appropriate tube or pipe, but first mark it with the depth of the old seal, so you'll know how deep to install the replacement. Be aware that input seals are different for '72-'73 versus '73-onward (below) when ordering. Porsche made a special sleeve, P382, to cover the clutch shaft splines when installing seals- a good safety measure.

[Dick Shift]

Originally Posted by Werkstatt

Jerry's idea about pushing the old seal (on late '73-'75 models) into the diff area, then pulling the diff to remove it, will work as an alternative to the Porsche tool. Find an appropriate tube or pipe, but first mark it with the depth of the old seal, so you'll know how deep to install the replacement. Be aware that input seals are different for '72-'73 versus '73-onward (below) when ordering. Porsche made a special sleeve, P382, to cover the clutch shaft splines when installing seals- a good safety measure.

Using a piece of pipe with a OD just a little smaller than the trans release bearing collar ID, MARK the DEPTH of the old sea. Oil and tap a new seal in pushing the old seal into the trans. Don't worry about retrieving the old seal. It harmlessly rides on the main shaft. Your done! A 10 minute job. I've done this dozens of time with no problems. Just make sure you have the correct seal for your year trans. BTW; best shifting with 90-140w trans oil. Aloha, DS

[Jon B]

Hi DS-

I think I just said that(?)- but I wouldn't leave the old seal in the transmission. The input shaft OD is much smaller than the seal ID (see below), it'll eventually move and get eaten by the ring gear. There's only about 3-4mm clearance between ring gear and shaft, depending on diff shimming. Would you know when it happened? Probably not- it'll get munched and pushed foward. It'll work, but it's not a good thing to do. Oil seals have steel shells.

[revmax]

Read Pete Zimmermann's 915 tutorial off the RedLine Technik site. Great read on the 915 box and very informative. Good luck...

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