[ds968]

it's been ten years since I had my pinion bearing repaired so I don't remember very well at what speed the noise kicked in but 30-35 mph sounds about right.. it was pretty constant in all gears, also when coasting in neutral, etc. but definitely more pronounced / loudest on gradual deceleration from say, 50mph to 10mph. But I could only hear mine with the windows closed and the radio off . Most certainly a jet landing and taxiing on the runway type of whine sound. The only way to be absolutely sure is to have another owner who had the pinion bearing problem ride with you. That's what I did, and within the first minute of the drive, he said : yup, beyond a shadow of a doubt it's your pinion ! It was.

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[Cloud9...68]

Well, I have to say, you're recollection of your symptoms do sound somewhat similar to mine. I found it odd that I can hear it best inside the car with the windows up, but that seems to match what you had. The tone of mine is different - more of a whistling/whooshing sound, like an air leak, but maybe the sound of these things varies depending on their wear pattern. I sure wish I know somebody locally (preferably a coupe owner, as I'm sure the sound manifests differently in a Cab) who had a 968 with a failed pinion bearing, as I agree that this would be the surest way to know. There are a few shops in town who actually work on these cars, so my best bet would probably be to take it to one of them and see what they think about the sound.

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[tamathumper]

If you tested the car with the wheels in the air, you can't rule out wheel bearings, as those will whine (or not) based on their load. It can change when turning left/right, accelerating/decelerating, etc.



If you tested the car when it was sitting still, and still heard the noise, it can't be air rushing past the car (hatch seals).



It's very curious that it is not speed dependent, either on RPM or MPH.

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[Cloud9...68]

Tama,



Yes, I had though about the issue of the wheel bearings not being under load, but I don't know how else to test for whether they are making the noise. I'm not really sure if I was truly able to reproduce "the noise" with my sitting-still test - my assistant certainly didn't think he heard anything unusual, but then he doesn't own a 968 (he has a 964). The bottom line is that I don't know what I have, if anything, but my feeling is still that I'm hearing something that I don't think was there before, and I can't image what besides a worn pinion bearing could be making a noise from the back that matches the symptoms of what I think I'm hearing. If I were to make a guess at this point, I'd say I'm in the very early stages of a pinion bearing wear issue, and I never would have noticed it if I hadn't been driving by car with the rear seat and cargo area padding/carpeting removed. I just need to take it to someone who is familiar with the problem to confirm.

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[ds968]

[quote name='tamathumper' timestamp='1375620011' post='146533']

It's very curious that it is not speed dependent, either on RPM or MPH.[/quote]



Not sure how to describe this accurately but it IS mph dependent, just not "louder" per se, so you can tell the whine also speeds up with acceleration, and slows down on deceleration but not in terms of DB levels. Not RPM dependent at all .

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[ds968]

[quote name='Cloud9...68' timestamp='1375624858' post='146537'] I just need to take it to someone who is familiar with the problem to confirm.[/quote]

If you want to wait until November when I'm there for tne Formula 1 , I'm sure we can probably find some time to meet up and go for a ride. However, if the sound changes at different stages no guarantee I'll be able to tell with 100% certainty, because I can only compare it to mine, but I'm still thinking I can diagnose a pinion sound regardless of stage with better than 75% confidence factor.

My bearing had only one single dimple, tne size of a pinhead, barely visible to the naked eye and it still produced a sound I could hear. The shop that did the job, and they have repaired around five other ones on 968s before mine, said I could have driven the car with that probably for a quarter million miles and it would not have gotten much worse...as long as the noise did not bother me. But it annoyed me to no end , so I had to fix it. However, I've seem photos of other bearings that were so badly pitted, the owners

must have driven like that for tens of thousands of miles before the noise probably became loud enough

where they could not stand it. One of the problems is that many shops, even those who have worked on

other 968s but not on the pinion will listen to the sound, and tell you its normal forth trannies in these

car's, especially with hatchbacks that amplify every suspension and rear tranny sound, so people leave it alone.

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[Inkedupfatboy]

If DS (Dan) only had one tiny, tiny dimple, then when you look at the photo of my bearing, the largest pit was a full 1/4 inch or more and several of the roller bearings on the entire bearing were worn...that might explain why mine was not "jet engine' whiny and just enormously loud...



I am an hour away from Daytona and was able to find a good shop, I bet being in a larger area like Austin, you should be able to use the interwebs to find a guy.

Good luck.

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[AJG]

This discussion about bearing preload takes me back a LOT of years to the last time I changed a tailstock bearing on a cnc lathe. I vaguely remember about a spacer behind the tapered race which acted as a stop so that with the lock ring pushing the bearing up a taper to butt out against this spacer you would end up with a 1 micron interference fit as the bearing inner ring swelled out as it progressed up the taper. The taper was 1 in 17 so that the length movement gave you some tolerance to achieve the fit (allegedly)ie 17microns movement lengthwise! All this waffle brings us to the fact that its very easy to overload a bearing. We are talking miniscule tolerances. Check out bearing manufacturers websites about bearing fits in general and you will get the idea. A tapered roller bearing is very difficult to deal with. Its all about putting the bearing together and measuring very accurately where end faces are in relation to each other, measuring where there going and what butts up to hold them in place etc.

Sigh! Its not easy. I wonder how the "special tools" set the bearings? Surprised it was left to a robot assembly at the factory.

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[Inkedupfatboy]

I basically heard that the entire issue was because the robots set the incorrect preload on the bearings to begin with.

I just hope my guy got it right and I won't have to hork up another 3 grand to fix it again. sigh.

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[tamathumper]

Once the tranny heats up, I'll bet if moves a lot more than a micron, and if the shaft grows more than the case, that bearing takes a lot more load.

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[Chris Vais]

I drove my car, out of necessity, for a period of time with a bad pinion bearing. Initially, it was just barely audible, but got progressively louder. The pitch didn't change with speed. By the time I replaced it, the howl sounded like a jet engine at full throttle, the noise making the car unbearable to drive for more than a half hour. Any other transmission bearing would likely make a whining sound, if it was damaged. That said I don't believe that we have ever had an owner report, on the forum, any other kind of transmission bearing failure.

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[ds968]

The shop that repaired mine ( and again they worked on several 968s pinion bearing ) said there is essentially a negligible at best, but probably no risk at all, absent something else in proximity of the bearing going wrong, of anything else happening, but an unbearable noise. According to them no matter how much pitting you have, the composition of the metal as well as the setup of the bearing does not lend itself to pieces breaking off of it and "grenade" into the other parts of the transmission, nor is it likely to lock up / freeze and cause a failure that way.. HOWEVER, this was only one opinion, I WOULD NOT SUGGEST ANYONE TEST THAT THEORY, it's not worth the risk even if that possibility is 1% and it has not happened to anyone else...yet. But there is a relatively high confidence level if the noise is mild you probably have quite a few miles to go before it gets to a stage where that risk might become to close for comfort .

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[Inkedupfatboy]

look at the photo of how much had come out of my bearing - and that was only one of the bad spots -

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[Cloud9...68]

Well, I just got back from a visit to a local European specialty shop, where their lead tech, a Porsche certified mechanic who has replaced several 968 pinion bearings in the past, took it for a spin with me in the passenger seat. He told me it the sound doesn't sound anything like a pinion bearing, nor is it a wheel bearing. His opinion is that all I'm hearing (and it seems to be more audible from the drivers side for some reason - I was struggling to hear it from the passenger seat, and we had to get it well over 60 mph before he agreed that there was a bit of louder-than-typical noise coming from somewhere in the rear). His opinion was that all I'm hearing is standard gearbox noise, which is more noticeable in my car because I have several of the interior panels out (because the roll bar is in the way of reinstalling them without modifying them, which I haven't gotten around to yet). Also, he postulated that the fact that the roll bar is welded to the chassis in multiple places, the roll bar itself may be transmitting some sound/vibration from the gearbox via the chassis in a way that the average 968 wouldn't. So when I said, "So, you wouldn't recommend going ahead and yanking the tranaxle?", his response was an emphatic NO! Coming from someone who stands to make a fair bit of money from the rebuild, I felt like it was a valuable opinion, which was also shared by my neighbor who helped me with my test over the weekend.



Dan, I may still take you up on your offer of going for a spin in it in November (it is a coupe, so the issues Craig Woodman raised about two men riding together in a Cab will not apply <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />), as I'm still not 110% convinced I'm not in the very early stages of a pinion bearing problem, but for now, I'm going to leave it alone and listen for any noticeable change in volume or tone.



By the way, I was thrilled about the comments he made about the car. He felt the ride was not overly punishing, considering the mods, and opined that it would be fantastic on the track. Very cool.

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[Inkedupfatboy]

good to hear -

I also plan on having my best bro with me in the car since he is jealous as hell - two guys in a cab comments also not withstanding ...

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[Rap]

Man youse guys is living on da edge! Couldn't you put a blow up doll in the back? She is very accommodating and doesn't prattle on!

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[flash]

you sure you could live without her for a while?

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[tamathumper]

What's the emoticon for "O' snap!"?

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[Inkedupfatboy]

   

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[ds968]

[quote name='Cloud9...68' timestamp='1375736968' post='146623']

Dan, I may still take you up on your offer of going for a spin in it in November (it is a coupe, so the issues Craig Woodman raised about two men riding together in a Cab will not apply <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />), as I'm still not 110% convinced I'm not in the very early stages of a pinion bearing problem, but for now, I'm going to leave it alone and listen for any noticeable change in volume or tone. cool.[/quote]



Absolutely, but definitely good to hear tne exlerienced mechanic's impression.

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