450knotOffice

My 996 has 137,000 miles on it, mostly on the freeway (although it has had a few track and autocross days thrown in for good measure). About 35,000 miles ago, I began to notice a faint whine - similar to the sound that straight cut gears in racing transmissions make - emanating from my transmission area. It would present itself mostly while load was applied - either through acceleration, or deceleration - and would quiet down during coasting.

I eventually had my friend/Porsche mechanic take a look at it, and he told me it was either the Pinion bearing, which has a history of drying out and failing with these transmissions, or possibly the Carrier bearings, which can make a similar noise, but are a lot cheaper and a lot easier to replace.

He was about to pull the transmission for a clutch replacement and while in there was going to replace the original IMS with the updated LN Engineering version and also replace the RMS. We figured - while the box was out - why not replace the cheaper Carrier bearings first and see if that solved the problem.

Well, it didn't.

I was up to my eyeballs in expenses at the time and the last thing I could afford was a full transmission teardown to replace the obviously worn Pinion bearing - at least for a while anyway (without putting it on my credit card, which I'm hesitant to do these days because I paid off my cards a few years ago want to keep myself off of that crack pot for good). He mentioned that the transmission would almost certainly NOT self destruct over the short term - it would just get louder and louder. So I put it off.

And I put it off.

For about 30,000 more miles.

Well, it got SO loud that eventually it became deafening at highway speeds. It was awful. I mean, I couldn't even hear the engine over that racket. Interestingly, it never lost its shifting smoothness through all of that. At least until it got so bad that I decided I was playing with fire and decided to park it. The final straw was that I was feeling a weird vibration in the stick in second gear and the lever did not slot in on the upshift to second without a little hesitation and shudder. Uh Oh! Ok. I give up. Time to park this thing.

So, I called my friend and told him it was parked until he rebuilt the transmission (which he gave me an AWESOME labor deal on, btw). A few weeks later, I drove it to the shop he uses for his little side jobs (a place run by another friend of ours) and we immediately tore into it. In no time, the transmission was out.

He sent it to another guy he knows who has the equipment to press the gears and bearing off of and on to the tapered shafts. He called me a week later and told me that they had NEVER seen a bearing as trashed as mine! I was not surprised. Look at the pictures below... The ball bearing cage was coming apart. The ***** themselves were so worn they weren't even round anymore, and the inner races were scored beyond belief. Take a look at how much metal sludge is on the magnet. There was so much bearing material floating around that the carrier bearing he replaced the first time were trashed again, so I had to buy new ones - again. In fact, I decided to buy all new bearings for the transmission and differential. If it was a bearing, I replaced it. In all, I spent about $1350 on bearing alone.

Luckily, the gears and syncros were all unscathed. They were all in nearly perfect as-new condition, thank God. The Spider gears, which apparently have a tendency to become pitted over time, were perfect. No pitting whatsoever

Considering that the Pinion and Input shaft bearings are sealed units similar to the infamous IMS bearing, with the same inherent issue - namely the grease eventually exits the bearing, yet the transmission oil can't seem to get back in very well to lubricate the bearing - my mechanic decided to pull the seal off the new bearings in order to allow the transmission oil to lubricate the bearings, just as it does all of the other internals.

He's in the process of putting it all back together and I should have the car back on the road by the end of the weekend. I'm looking forward to the peace and quiet again.

A few things to be gained by this episode. One, unfortunately, due to the design of the bearings for this transmission, it seems that more and more of these units will begin to exhibit the same bearing failures we all know so well with the IMS issue. Two, DO NOT wait as long as I did to tear into the transmission once you begin to hear that whine or howl. Luckily for me, it seems that this transmission is quite robust - even when doofus me neglects it to the point that I should probably have my Porsche card permanently taken away from me. For an unreal number of miles, it soldiered on as I continued to drive it with a failing bearing. Amazing, really.

Here are some pictures:

jackarelli

Hi,
Great write up!
I drove mine with that wine for about 7k and it drove me mad! Don’t know how you managed that for so long!
When my mechanic removed the bearings they said that they were the worst pinion shaft bearings that they had ever seen. I’m sure not as bad as your 35k bearings though!
I too opted to have all the bearings replaced.
What a difference!
I now change the transmission fluid every service.
Jack

washington dc porsche

Been there done that.. :-) I drove mine only 10k extra miles.

Ubermensch

I'm glad you got things resolved, but I'm surprised you opted to remove the seal on a stock bearing. The first one last quite a while. I'm no bearing expert, but I thought splash lubricated bearings were usually used in environments with relatively clean oil. In the transmission I'd think the metal particles that are generated would cause problems with an open, metal bearing setup. Ceramic bearings would seem a little safer. Again, I have no direct experience with this, just putting a thought out there. If it were me I'd certainly change my transmission fluid on a more regular basis if I had an open bearing inside of it.

-S.

pszikla

Same story!
My pinion bearing was almost in pieces when pulled apart, yet the transmission soldiered on for a year until
the rebuild was done. Very noisy but never let me down.
Rebuilt by Gbox and shifts like a dream and whisper quiet now!
Pete

soverystout

Yeah, I have to agree here. At startup, the factory tranny fluid is thick and takes some time to heat up. It is also sitting in the lower half of the trans. What will be providing lubrication to the being while the trans fluid warms up?

If you pack the bearing with grease and leave them unsealed, the grease will be removed after the first hard, high temp drive.

Did you ever change the tranny fluid under your ownership and/or do you have proof that is was ever changed?

dennis hiip

Thanks for the write up and photos.

450knotOffice

Thanks guys.

I'm not worried about the lubrication of those two bearings. The third bearing I replaced is an open design, and there are about four or more other needle bearing buried in the gear stacks. Those were deemed to be just fine. No wear. Not only that, but as far as I know, Porsche never used sealed bearings until this transmission. Not so surprisingly, those others are not known for bearing failures. Also, "Robin 993DX" has already done this - about 1 1/2 years ago. As far as I'm aware, all is still well with his transmission.

Transmission oil changes will become a regular maintenance item for me now. Cheap insurance compared to another teardown.

Turkertwo

450:
Great write up. I will change my tranny oil soon. Those gears must be really tuff stuff to look so good coming out of a metal bath like you had going.
I have become a big fan of tranny music since going to a single mass flywheel.

buckaroo76

Looks like I have the same problem as well. Do any of you have a service manual for an 02 C2?
I'm gonna tackle this on my own, just need something to follow incase I get stumped.

Also does anyone know if its possible to use an unsealed bearing? seeing as how the complete bearing is inside the tranny, i dont really see a need for a sealed unit. Let the oil flow in and we will minimize our problems. IMO. Someone please correct me if I'm worng.

jrgordonsenior

I'll start a new thread but if anyone's interested, I have a G-Box rebuilt trans sitting in my garage that I'm going to sell. Details on a new thread.....

Viper6

What gear/trans oil did they recommend or do you plan to use?

GTgears

Step 1: Purchase a 50 ton press

450knot,
I am amazed with that many miles that your ring and pinion didn't eat itself. That's just unheard of...

450knotOffice

No kidding! It was perfect though, as you can see. Looked brand new.

My transmission is whisper quiet these days. Love it.

GBoxguys

I am not too sure that I would recommend trying this particular rebuild on your own. It is certainly possible if you have the correct tools, but it is also pretty easy to make things worse if you don't.

As to the bearings, you can always pull off the seal rings on the bearing and allow this bearing to sit free flow in the oil. I am not sure if this is going to be a better solution or not, but it is certainly an option.

I am glad to hear that you got your gearbox up and running again. I agree with Matt with relation to the ring and pinion not getting damaged, you got pretty lucky on that one. The rest of the gearbox looks like it was in great shape.

Erik