Replacing the 915 shift shaft seal - in the car - painlessly

[dtw]

While doing some work on one of my 911s the other day, I had it jacked up in the rear. Eventually I noticed, with a sickening feeling, the expanding pool of fresh Swepco in the driveway under the middle of the car. It was dripping down from a tiny drain hole in the center of the tunnel. There's only one (common) diagnosis for that - failed shift shaft seal. The transmission fluid travels down the shift shaft boot and gets dumped in the tunnel. If your outer shift shaft boot is missing or torn, then the fluid probably just dumps under the car.

My worst fear was that this was going to require a drivetrain drop. Nope! However, all the threads I read when researching this seemed to suggest extraction of the old seal from within the car, using various methods...seal extractors, sheetmetal screws, etc. That sounded nightmarish at best. I took one look in the tunnel and knew that was way over my head - there had to be a better way. There's just no room to work from the tunnel.

My wrench gave me some great advice and I tried it out. Here are the steps I ended up taking. Note: All prices are per Pelican Parts and are as of this writing, 7.30.09.

Supplies/tools
-New seal - 999.113.185.40 - $4.00
-Drip pan/container
-Shop rags & can of carb cleaner
-Medium phillips head screwdriver (remove tunnel cover)
-Small precision flat blade screwdriver (pry out old seal)
-Medium general purpose flat blade screwdriver (additional leverage)
-Metric allen wrenches (remove shift coupler)
-Emery cloth
-Small file or dremel tool (as needed - to dress burrs on shift shaft)
-Fresh motor oil
-Gasket/seal compound such as Curil T - optional
-Seal installation tool (in my case - improvised 15mm ratcheting swivel-head wrench)
-Mallet & drift

Procedure
1. Pull back accordion-type outer shift shaft boot from shift coupling.

2. Remove allen bolt from shift coupling; knock shift coupling free of shift shaft.

3. Move shift linkage rod and coupling out of the way (the threads I researched advised complete removal of the shift coupling - I did not find this necessary - I had enough room to work with the coupling still attached to the shift linkage rod in the tunnel)

4. Remove inner shift shaft boot. The inner and outer boots may be trashed due to being soaked in gear oil.

5. Put car securely on lift or jackstands - so that you have enough room to work under car at the nose of the transmission. If possible, the front of the car should be just higher than the rear, so as to minimize loss of transmission fluid.

6. Get under the car w/your screwdrivers, a catch pan, and shop rags. Using a small, precision, flat-blade screwdriver, extract seal. I carefully slid the blade into the ID of the seal, between the seal and the shift shaft. Then I turned the blade up, such that the screwdriver shaft was roughly perpendicular to the shift shaft and the ground. Executed properly, the tip of the screwdriver will now be engaged in the metal flange of the seal. The metal OD of the seal will protect the transmission case from the screwdriver, and the blade is away from the shaft itself. The seal can now be pried out of the aperture in the transmission housing. Use the lip of the transmission aperture to pry against the seal. This will require a lot of force for a small screwdriver, so be careful not to bend it. I actually used my free hand to apply another much larger screwdriver under the shaft of the smaller one, to help it out. The seal popped out immediately but with significant effort.

7. Move your container under the nose of the transmission to catch the fluid that will start dripping. I only lost a couple ounces of fluid during the entire job. Wipe up any mess on the car's underside from the leak.

8. Move back into the interior of the car. Withdraw the old seal from the shift shaft & discard.

9. Inspect the shift shaft. They will often have burrs at the coupler threads, rust, etc. Carefully dress down any burrs on the shaft. Use emery cloth or fine sandpaper to polish up the shaft and remove any surface rust. Flush & clean the sealing surface area of the shaft; inspect for any flaws that may have damaged the old seal. Inspect the transmission casting - are you sure it was a bad seal, and not a cracked case? After dressing/cleaning/inspection, I wiped the shaft down with some fresh motor oil and prepared to install the new seal.

10. Lube the new seal's ID with fresh motor oil (or your favorite seal lube...)Carefully slide the new seal onto the beveled end of the shift shaft, and past the threaded hole for the coupler. Move slowly and carefully here, feeling for snags/burrs that may be damaging your new seal. Slide the seal up to the transmission case, and ensure it is squarely seated against the case.

11. Using a seal installation tool, tap the seal home with a drift and mallet. I had just enough leverage to do this from within the car. Not having a seal installation tool, I found a great substitute. It was a Craftsman swivel-head 15mm ratcheting wrench. It slid over the shift shaft and covered the seal's outer surface perfectly. The seal should be flush with the casting when installed, not pounded down into the casting. This work area is so difficult, and the seal is so small, that I would not risk direct hammering on the seal. Buy an installation tool or improvise like I did.

12. Button up. Install inner shift rod boot, shift coupler, outer boot, tunnel cover, etc. Clean up any mess in the tunnel from the gear oil. Check for proper shifter operation. Overall difficulty is about a 2 or 3, overall time for job is an hour or less, including placement of 911 on stands.

But Dave, what about...
...Curil-T? There are a lot of fans of this stuff, and I use it religiously on engine work. However, transmissions and their sealing surfaces live different and easier lives than engines. I've built several leak-free 915s using nothing more than Loctite 574 on the paper gaskets, with seals installed dry. In this install, I don't think I could get the aperture completely free of transmission fluid so that I could safely apply Curil-T. So, I left the Curil T in the toolbox. If you really want to use it though, then I recommend a complete drain of your transmission fluid.

While you're in there...
...you should inspect other common replacement parts and consider replacement.
-Inner & outer shift shaft boots, particularly if they have been damaged by the gear oil deluge. Outer: 911.424.294.00, $12.25; Inner: 911.424.292.00, $20.00
-Shift coupler bushings - Pelican PN: 99.1758.424.M230, $9.50/pr
-Shifter housing bushings - ball cup and shift rod guide bushings. Ball cup: 911.424.139.00, $7.00; Shift rod: 914.424.224.00, $6.50
(Note: Pelican sells all 4 shifter bushings - 2x coupling bushings, ball cup, and shift rod - in a kit for $23.00. See Pelican PN: PEL-BUSHKIT1N)
-Transmission mounts - 911.375.043.00, $20.25-$27.00/ea, 2 req'd.
-Swepco 201 gear oil - Pelican PN: SWE-201-80W90, $54.25/gal

[BK911]

Good job and nice write up.

I think you got lucky removing the old seal. There were some that I had difficulty getting out with a slide hammer.

[dtw]

Maybe. But that's how my wrench does 'em...

[RWebb]

beside a puddle of oil below the nose of the transmission, you may also see this:

[azasadny]

Nice write-up. Thanks!

[dtw]

What are we seeing there, Randy? A little drip of gear oil at the shift shaft seal?

[svandamme]

Originally Posted by BK911

Good job and nice write up.

I think you got lucky removing the old seal. There were some that I had difficulty getting out with a slide hammer.

ditto, that seal can be near impossible to remove at times..

[RWebb]

Originally Posted by dtw

What are we seeing there, Randy? A little drip of gear oil at the shift shaft seal?

that drop of oil is coming down the lip off of the seal, which is recessed

I couldn't get the camera to focus on the exact area I wanted - and got tired of scrunching under there after a while...

I crawled under there to see if the cables/wires to the starter were loose (nope - so my no crank must have been caused by something else) and I then noticed a small pool of gear oil under the nose of the tranny.

I may try to put a mirror up there and take a pic of the image in the mirror - will see how busy I don't get in the near future...

[gduke2010]

Thanks for the tech write-up. will know where to look when I replace mine.


Gary

[RWebb]

here is a better pic:



note the telltale streak of green Swepco - I did not have any gear oil in the body tunnel, so it pays to check for puddles below where your car is parked

BTW - I figured a right angle pick tool wold be perfect for ths - so tried that and a 45o angle one too - maybe a bigger one would work fine, but a small screwdriver worked best for me too.

I found it helpful to point a stubby LED flashlight down the shaft from inside the tunnel

[brd]

Thanks for the post!
I was under the car overhauling the heater system and saw the same tell-tale signs, oil drops at seal and oily around that drain hole. I'll put it on the list of less intimidating things to do now.

Much appreciated.

[SCadaddle]

If you'll put a small hole in the bottom of the boot that fits to the tunnel you'll never fill your tunnel with gear oil but rather see it on the ground when that seal decides to leak.

[isby]

I'm getting ready to do this job and saw Dave's excellent write-up above. Was wondering if anyone has any additional thoughts or comments on whether to use sealing compound (curil-t or other) on this seal when replacing. Thanks all.

[Mahler9th]

My application has been racing...

For the past 19 years I have not used any sealant on that seal. No issues.

If I recall correctly, a wise friend with 40+ years working on Porsche street and race cars told me that keeping the factory rubber boot in place helps keep dirt away from that seal. So I have followed that suggestion.

I generally consider that rubber boot as important as those on the tie rods.

My car is a '75.

[proporsche]

Originally Posted by Mahler9th

My application has been racing...

For the past 19 years I have not used any sealant on that seal. No issues.

If I recall correctly, a wise friend with 40+ years working on Porsche street and race cars told me that keeping the factory rubber boot in place helps keep dirt away from that seal. So I have followed that suggestion.

I generally consider that rubber boot as important as those on the tie rods.

My car is a '75.

yup this........^^^^^

[jlex]

Similar process for the G50?

[Funracer]

Just changed mine today. Your procedure to remove the old seal with a small screwdriver worked perfectly. Thanks