79SC 915 trans leak

[Robey5]

OK—- I have a new leak from at least one place on the 79SC that seems to have developed since last season. I have been able to do 2 early season shake-down runs, both around 20 miles and now we have an interesting leak from what looks like the access door on my 915.

... the fluid is blue, and does not look like it is coming from above. The passenger side looks dry (of trans fluid); and does not look like a “typical” place to have a leak.

Any pointers from those of you who have been able to address a problem like this in the past???



You can see a little blue drip developing on what looks like an access door.

[Robey5]

OK, I was able to get under there and snap a couple more pics.

It looks like we may have a little bit of a weep situation coming from the LH axle seal, but ... there is a lot more coming from what looks like the “access door”. Is there a gasket to be replaced here? (Assuming that I would do this job at the same time as a fluid swap; which ... it’s due).

[Flat6pac]

There is a gasket under the inspection plate but I still use 574 on that gasket, both sides
Be sure your in neutral when you pull the cover because the fork attached is part of the gear selection. Make sure the fork is not loose on the plate. If it’s loose, don’t tighten, replace the cover or you’ll be back there before you want to be
Bruce

[Robey5]

Ok; let me make sure that I follow here:

There is a fork attached to the inspection plate. There is a gasket that I need to replace there, and I need to get some 574 (locktite, I believe).

So that I am on the right track here ... is it plausible that this is where we’re leaking from?

[Robey5]

After a little google-fu....

I see that there is a fork there that aids in gear selection. (Thank you Bruce!)

.. I understand that the fork should not be ‘loose’ but ... it appears that there are bolts that’s hold the fork in to place, why can I not just tighten these dudes up if the fork is loose?

I am not really in the mood to have to go the rebuild route if I eff this up (...the trans was gone through in the 05 era, and there is not many miles on her since the rebuild). What will happen if I check the torque of these fork-to-plate bolts and tighten where applicable? This part (Tran-plate sub-assy) does not seem to be offered by our host, unless I want to get the version that has a trans cooler hose connection which is overkill for me.

The goal here is to button up the leaks and make this rig a more sorted machine; I do not race it or autoX, but do play into it occasionally in a spirited drive. I hate oil leaks, and this one seems like an ‘easy’ one to fix.

[Flojo]

Originally Posted by Robey5

[img]

looks like the seal between trans and axle is toast

[yelcab1]

I would think you have to solve the bigger leak at the axle than the little drop at the bottom.

[Robey5]

Flojo/Yelcab1:

Thank you for chiming in.

If the gasket is getting replaced on the "trans-plate" ... then the other leak is getting addressed as well.

The question remains about this fork - and if I can just torque it down if it is loose.

I believe that the axle seal can be done "in situ" (after I pull the CV joint) to address that leak. I have to believe that I can pull that axle stub from the trans to replace the seal (but I cannot remember).

['78 SC]

The "fork" in question. Gasket not installed but you can make out the shadow of where it fits on top of the access cover. These are the nuts that should be checked for torque. These were still tight. I added some loctite, just in case.


The transmission internals when in neutral. This is where you want everything when you re-install the access cover and fork. The tines of the fork surround the bulges of the shifter dongle (yep, dongle).

[Robey5]

Man; I love this forum...
Thank you for the pictures, '78 SC.

The final question that I have is ... can I tackle that axle seal in-situ? Or is that going to require an engine/trans drop? My thought is that we can remove the CV shaft (12 bolts and a big mess), then remove the output axle (on the GB), then replace that axle seal. Is there anything special that I will need to get for removing the output axle?

['78 SC]

Originally Posted by Robey5

The final question that I have is ... can I tackle that axle seal in-situ? Or is that going to require an engine/trans drop? My thought is that we can remove the CV shaft (12 bolts and a big mess), then remove the output axle (on the GB), then replace that axle seal. Is there anything special that I will need to get for removing the output axle?

That's pretty much it. If the CVs have not been serviced lately, would be an opportunity to remove the whole axle then clean, inspect and re-grease.

Once the CV is off, you'll see the head of the bolt that secures the drive flange to the differential. Remove it and the flange pulls right out. Pull and replace the seal. Wait, that sounded entirely too easy. A seal puller (google it) will help immensely. You'll need something to drive the seal (don't hammer the seal itself). Do a search here for how to install and how deep to install. Buy a spare seal (in case you munge one up).

[Flat6pac]

If the nuts are loose on the fork they are working the studs out of the plate, and they’ll do it again.
That’s why you replace.
Bruce

['78 SC]

Originally Posted by Flat6pac

If the nuts are loose on the fork they are working the studs out of the plate, and they’ll do it again.
That’s why you replace.
Bruce

Bruce, of course, is right about loose studs.

To clarify, in my case the studs and nuts on the shift fork were still tight. The loctite was to keep things that way. (The green loctite can wick between assembled parts to secure them.)

[Robey5]

OK —— Thank you for the clarification. Order placed for gaskets, Swepco, seals and a couple other doo-dads that I needed. I will update the thread when I start to chip away at this dude; once parts arrive.

BTW. 574 is ... expensive (per fl oz). I hope it really does it’s job on that inspection door gasket. Once I am able to seal this leak up, we will take an honest look at what else is leaking. (I will give y’all a clue; it’s a little more brown in color, and is annoying).

[Robey5]

I gave the car a bath on Saturday, and pushed it back into the garage to replace the axle seal yesterday.






Working on your back is no fun, and the seal did not want to come out of there (despite the leak). The old seal was frozen in place at the 12 o'clock position, and I gave it a little heat to finally get it out of there.





A couple things here of note for the next guy who is searching the forum to find how to do this:
The bolt that holds in the stub-shaft is a 17mm.

So long as the car is on 2 wheels (opposite the seal you're replacing) - you will not loose any gear oil.
Put the (new) seal in the freezer before installing. Lube the outer surface of the seal.

I will tackle the access door gasket next.

[Walt Fricke]

On the "access door gasket," it might be better to call it the fork holder plate, as while it is convenient for looking into the transmission, there is nothing to access or adjust through this hole - the plate must be there because you couldn't slide the center housing of the transmission over the gear assembly with the fork in place.

But more substantively, you don't need the gasket at all. Orange Loctite or the case sealant of your choice will do without the gasket. The slight dimensional difference involved makes no difference.

I learned this when I removed the plate to stick a crowbar up in there to straighten one of the cast shift rod parts on a Friday for a Saturday event, caused by an over vigorous and enraged attempt to engage 1st gear. This wouldn't be something to put in a factory service manual, but it worked fine. I've skipped the gasket ever since, as well as omitting the gasket between the center case and the tail case, which my local gearbox repair shop does also.

Be interesting to see what, if anything, you find wrong with the gasket seal etc. Not an area where a leak suddenly appears, I think.

Was that old axle seal that bad in place, or did removing do the obvious damage? One doesn't hear of these seals being an "oh, yah, they need replacement pretty often after 30 years or X miles". Of course, it is not unusual for these 915s to have been taken apart at least once by now, and the seals replaced as a "why not since we are there" item.

[Robey5]

The axle seal was one of the places where we had gear oil coming out. I am not sure what made it leak, but it was certainly one of the points that was leaking. I destroyed it while removing. I made sure that the aluminum on the trans did not have any scores or burrs before installing the new seal. Hopefully this will be tight again.

With the fork holder plate, I too am curious what is making it leak - the shop that did the rebuild years back used a fair amount of goo (brown in color) to try to seal it up, but it is certainly the other leak on this. Whatever the brown goo is did not hold the seal.

[Walt Fricke]

As I recall, the axle seal is one of the seals on a Porsche drivetrain which isn't inserted until it butts up against a stop. Which means deciding how far in to drive it. Either extreme can cause premature problems. Doubtless you hunted around for a spec for that.

[Robey5]

Walt .... you’re correct. I did not bother looking for the actual spec for the depth, which means that I may have the opportunity to do this job again. ... which is why I bought 2 seals from our host.

Regarding what I did find on how deep to go (because I was curious) —- there are a couple users on this forum who’ve indicated that the left seal is to go “a few millimeters deep,” and you are correct —- there is not a *hard stop* for the axle seal to sit on. So I pressed it in there (with my PVC chunk) and busted out the calipers to see that I had it in there past the chamfer and square, as long as the bearings are not rubbing on the seal, I cant see that it will cause any issues, but I guess that we will see soon enough.

[Walt Fricke]

My recollection is that if it is in too far, the inner part can rub against something - end of the diff? If too far out, the flange will rub. The flange side you can eyeball.