Early 915 tranny seal Questions

[mikes72t]

So my tranny is leaking a lot of oil and the mechanic says it might be one of the early ones with a main seal that must be installed over the entire length of the shaft from inside the transmission. If so he says it would be better to buy a new tranny than try to seal up the one I have.

Was there a recall of early 915 tranny's? Did the main shaft seal design change during early in 915 history? How hard is to reseal a leaking transmission? Will any 915 fit in my 72 or do I need to look for a similar early unit? How can you tell buying a used tranny if it is any good? Currently I only grind first if I try to go into it too quickly from a stop.

Thanks for any help you can provide.


Mike

[ChrisBennet]

Someone like Wevoid can answer this more completely but until the experts chime in...
The '72 915 has the stupid input shaft seal that must be installed from the inside. Doh! The seal was fixed mid '73 I think. A friend of mine had his '72 transmission built by an expert and when he got it back it leaked from the input shaft seal and he had to send it back. Perhaps there is more to this early seal thing than meets the eye.
-Chris

[Grady Clay]

Mike,

If the mainshaft seal is leaking the oil goes directly into the clutch causing clutch problems more than oil on the ground.

If you are sitting at a stop and suddenly depress the clutch and pull the shifter into first gear and get a crunch, which is not unusual. Porsche designed the first gear syncro to not provide much synchronization in this direction in order to gain better synchronization in the “down shift” mode. This also could be related to an input shaft seal leak because an oily clutch doesn’t release correctly.

Yes, all 915 transmissions are interchangeable – sorta. The biggest differences are clutch linkage, axle flanges, and speedometer. I am not competent to tell you which will fit your car. For instance, I can tell you that you can use your nose piece and speedometer drive will fit on a 915 with the electronic speedometer in order to use your mechanical drive speedometer. There are many other issues you can solve on this forum. Regardless, you should end up with a properly done 915.

Best,
Grady

[zotman72]

Yes your whole tranny internals have to come out to get this seal in. It took three tries (once me and twice my mechanic) on my case to get it right too. Let me tell you that it is a royal torquer to see tranny fluid leak out after you just put it together and inserted it back with the engine into the car. Not the cheap tranny fluid either (Redline and Swepco)
A hot tip is to drill a hole at the bottom of the shaft sleve such that if tranny oil leaks pass the seal, it goes down into the bell housing and out the inspection hole, rather than get to your clutch and pressure plate.

No hold onto your early 72 tranny, it has beautiful brass cages for bearings and brass elsewhere. Later Porsche got cheap and went with other metals in there. If you going to replace the seal, you might as well do your dogteeth and syncro rings for 2-3, 3-4 at least. HTH.

[john walker's workshop]

a shop called me the other day, looking for a diff housing, and said their mechanic actually broke off the guide tube on a 72 because he was sure it just had to come off to replace the seal. definitely more work than the later trannys, but not enough to actually replace the trans to do it.

[Grady Clay]

Bill,

You are right on. In addition the “drain hole” you can add a second “seal” to act as a dam to prevent leaking oil from getting to the clutch. This is applicable to 901 as well as the other 915s. On a 901/911/914 all you have to do is grind a drain slot in the TO tube down from the input shaft seal. Make yourself a tool to press in the auxiliary seal so it clears the clutch disc hub and sits squarely in the tube (901 or 915).


John,

It’s amazing what a little lack of knowledge can do. I have seen some early 915s with the tube machined off and a replacement fabricated. More work than changing housings.

Best,
Grady

[mikes72t]

Guys:

Thanks for all of the replys. I am nervous about this job but I can't afford to pay the shop to do it. Do any of you have pictures of what i can expect to see and how to do this.

Wayne: I don't suppose you want to write a book about this transmission in the next week or so do you? Kind of tough from Florida I am guessing.

Thanks again everybody.

Mike

[rs911t]

The other night a couple of us changed this seal on my 915. Yes,
you must remove the innards to reach the seal. Then, it's a bit
of a trick to get it out and the new one in. I'll find out this
weekend if we succeeded.

it has beautiful brass cages for bearings and brass elsewhere.

Right on! Lots of intricate, shiny steel and brass. Cool!

[wevoid]

Mike,

Anyone who knows me knows my penchance for '72 911's.....

Also in conjunction with all the work Windrush has done on 915 transmissions, it seemed logical to develop a solution for the '72 input shaft seal - even if only for selfish reasons !

We have a machining operation and replacement guide tube that solves the problem and expense of input shaft seal leakage on the '72 and all non-bolt-on guide tube 915's. (early and late '73's)

We machine the final drive housing to accept a new guide tube. The guide tube has the seal correctly positioned for the '72 input shaft. The Guide tube is retained by a large circlip, that can be installed or removed with the side cover removed from the final drive housing and differential removed (a 10 minute job). The guide tube is sealed in the housing by the same O-ring used on later 915's.

When the job is complete, the final drive housing has a new steel guide tube that is easy to remove without disassembling the trasnmission and uses the later model input shaft seal that is common on 915's up to 1986.

Regards

Hayden

[Grady Clay]

Hayden,

Good for you. Thanks from all early ’72 owners.

Please e-mail me, I’ve got some more ideas for you.

Best,
Grady
gradyclay@hotmail.com

[Sonny]

Hey guys, I have been dealing with a huge leak on a 915 I just installed ( and yes, just pulled everything back out of the car !@#%%^)

It is a 915/3.0 out of an 83 SC. I guess I don't really know what model year the transmission is. Now when I removed the gearbox and then pulled off the guide tube I found that the damn mainshaft seal was not even in place. It had worked its way off the guide tube and along the shaft into the gearbox. What would cause this?? Looking at the seal "land" at the end of guide tube I am thinking OK, well what the heck is supposed to stop the seal from coming off the guide tube in the first place??? why is there not a snap ring or something like that. ???? Does this description sound familiar to you guys??

[Eugene at Pelican Parts]

Originally posted by Sonny
Hey guys, I have been dealing with a huge leak on a 915 I just installed ( and yes, just pulled everything back out of the car !@#%%^)

It is a 915/3.0 out of an 83 SC. I guess I don't really know what model year the transmission is. Now when I removed the gearbox and then pulled off the guide tube I found that the damn mainshaft seal was not even in place. It had worked its way off the guide tube and along the shaft into the gearbox. What would cause this?? Looking at the seal "land" at the end of guide tube I am thinking OK, well what the heck is supposed to stop the seal from coming off the guide tube in the first place??? why is there not a snap ring or something like that. ???? Does this description sound familiar to you guys??

Are you sure you didn't push the seal too far in when you installed it? It should be centered onto that 'land' in the guide tube. Although there is no snap ring as you suggested, it should be a pretty tight fit. Any forces exerted by the input shaft spinning within it should be negligible.

[mikes72t]

So let me understand. Fomr another thread it could be my vent hole "peeing" oil or it could be the main seal that is leaking out on to the clutch and the flywheel is throwing it everywhere?

If the oil leaks on the flywheel and clutch wouldn't your clutch slip and be really obvious or is it not really noticeable once the clutch is engaged?

I am curous because the oil is droppin off the tranny from the end by the mounts at the front of the car at the opposite end of the clutch flywheel, but if oil is flying out of the inspection hole that could explain the oils travel I guess.

Wevoid: Could you email me more details about the fix for 72's? Would I have to ship you the whole tranny or just part of it? How much does the procedure cost? Etc?

Thanks

Mike
mikemccannell@columbus.rr.com

[techweenie]

I have to correct some misinformation here.

The internal mainshaft seal was not replaced until midway through the 1973 model year. I've seen April '73 build cars with internal mainshaft seals.

Hayden: looking forward to using your solution on future trans overhauls!

[Eugene at Pelican Parts]

Originally posted by mikes72t
So let me understand. Fomr another thread it could be my vent hole "peeing" oil or it could be the main seal that is leaking out on to the clutch and the flywheel is throwing it everywhere?

If the oil leaks on the flywheel and clutch wouldn't your clutch slip and be really obvious or is it not really noticeable once the clutch is engaged?

I am curous because the oil is droppin off the tranny from the end by the mounts at the front of the car at the opposite end of the clutch flywheel, but if oil is flying out of the inspection hole that could explain the oils travel I guess.

Wevoid: Could you email me more details about the fix for 72's? Would I have to ship you the whole tranny or just part of it? How much does the procedure cost? Etc?

Thanks

Mike
mikemccannell@columbus.rr.com

Mike,

Besides the case gaskets, I think you're familiar with all the places your tranny could leak except for one. So far, you've discussed the main shaft seal which would spray the clutch with fluid, but actually not tremendously affect drivability. You will notice clutch shudder (that will get progressively worse), but it should still engage. Next is the vent hole which must face towards the front of the car, or else it will spit fluid. That's an easy fix. Another place is the flange seals, but that would be rather apparent because fluid would be seeping from behind the CV joint(s).

However, since you are now pointing to the tail of the transmission, you may not be aware of the shift rod seal. If the rubber boot is still slipped over the transmission end cover protrusion, a large percent of the fluid leakage will be evident within the shift coupler compartment underneath the panel between the rear seat area. Check in there. If it's at all wet, then that seal's blown. Other than that, the case gaskets are prone to seep, but the amount of fluid is quite negligible. It could be a combination of several of the aforementioned spots and most likely is.

How many miles are on the tranny? Does it still shift well? How much does it really leak? Consider what you have and what you want in order to decide whether or not you actually need to have it all rebuilt while it is apart. Hope this helped.


EDIT: Ahh... just remembered a few more bits and pieces. The speedo angle drive has got a small seal, and the reverse shaft has an O-ring at the end of it. Detent plugs might also squeeze out a drop if not tight enough, but nothing I just mentioned is much to worry about. I think that's all of it though. Good luck.

[mikes72t]

Eugene Thanks:

The tranny has an indicated 82k miles but I have only had the car about 6 months and it might have rolled once already. While the engine and tranny were out for the engine swap (just another 2.4T) I topped up the tranny with fluid and the first drive around the block had a noticeable trail of fluid. The tranny seems to shift okay, it is more effort and slwer than the BMW but this is the only Porsche I have ever driven so I assumed it was normal for Porsches. The leaking is much slower now just leaving a few spots under tha car and noticable gear oil odor.

When the car was on the hoist there were several spots that the oil was dripping off of the front near the tranny mounts.

I will check the vent hole. (I can dream right) and then I will probably have to drop everything again to check it further.

Thanks for all of your help.

Mike