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Whirling noise when driving over 30MPH. What could it be? Drive train

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I have noticed that there is a whirling noise coming from the rear end of my tiptronic C4S once I start to drive at over around 30MPH. I don’t this it is coming from the engine as if you engage neutral while driving the noise is still there.

I am wondering if it may be coming from the gearbox or drive train. I think I remember someone once saying that if it were a wheel bearing then it should be more obvious when I go one direction or when I change direction but during a quick test last night it didn’t appear to be any less or more obvious based on which direction I was driving.

As this is my first 911 I don’t know if this noise is ‘normal’ per say but I doubt it. Any ideas on what it may be and has any of you ever experienced this on your cars? Many Thx

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Hmm now I think the noise may be coming from the front and after some internet searches I have discovered quite a few C4S's and 996 Turbo's which have had front diff problems - noise etc.

Was you able to replace the seals and this fixed the noise? Does this also mean that the noise is because the oil level has become low - if it is the differential that is.

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Out of interest does anyone know if adding one of those gearbox/differential additives which claim to reduce noise and add extra lubrication actually work? If so I was thinking of trying that with an oil change before going down the differential rebuilding route.

And if it is indeed the differential making the whining noise is this most likely due to worm bearing/s?

Does anyone know what oil to use in the diffs? 75w-90 semi synthetic?


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Early wheel bearing failure (40K miles or more) is pretty common on these cars. Just did one of mine last week with 45k. The 30MPH range is typical of when the noise can be heard inside. If the noise is independent of if the clutch is depressed or not, it is probably a wheel bearing. It is usually pretty easy to audibly tell which side the problem is on, but determining front to back is more difficult (at least on my Boxster). W/o the front wheel drive, you can remove the wheel and brake pads (5 min.) and spin the hub. If noise or roughness is felt, you found it. If you think it is gone, but not positive, remove the caliper and rotor. The bare hub has a fraction of the inertia of the disk, and your sense of bearing "feel" will be amplified several times. With a half shaft in place, it is more difficult to isolate noise and feel this way (the CV's add drag and ball movement is not as smooth as a bearing. Suspect you may have to put car on a lift with engine running and in gear. A stethoscope placed on each bearing carrier will quickly let you know which has failed. Other readers may have alternate methods.

On the rwd 996/986, the rear wheel bearings are pretty easy to replace for the home mechanic (using the B90 type pullers described in other wheel brg forum messages). You have to pull the 6 socket head cap screws holding the inner cv to remove the 1/2 shaft, NBD. The

fronts are another matter. The front hubs won't let conventional pullers like the B90 work until the bottom end of the McPherson strut tube is moved out of the way, and the stub axle removed. This requires compressing the strut spring/disconnecting suspension links, etc.. Lotsa special tools and hours. This means the home mechanic has to be the determined type.

We do a lot of bearing work (see Casper Labs IMS bearing in forum). On the wheel bearing I replaced last week, a special puller was made that lets you leave the 1/2 shaft and/or stub axle in place!! No axle removal, no suspension disassembly. Old bearing out/new bearing in in 30 min. (for average wrench twister). Only drawback to the tool is that it is specific to one size bearing. For example, the Boxster S bearing is larger, and will require 2 different parts.

We have a pic of the prototype tool, but I have't the time at the moment to figure out how to attach it. Any one who wants to see it... just email me (N1WR@juno.com). We have material ordered to make a few production tools, to see if anyone is interested.

Bill Ryan

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Here is the prototype puller with the bearing just about out. It is rough looking, but the production tool will be professional grade. This is a very robust puller, and will pull hundreds of bearings if used properly. Don't ask to see the mechanism, we will not tell you. Sorry, if you want to see how it works ...you will have to buy it

Bill Ryan


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Thanks Loren, The B90 is a very popular tool with the Porsche community,.... high quality. BUT, we have taken it one step further by eliminating the need to pull axles/hubs/compress and partially remove front struts to get the old bearing out and new one in (req'd with the B90). This will save the amateur mechanic about 4 hours (pro...at least 2hrs) on a front bearing,.... with no need for additional tools (spring compressors, joint separators, etc.). The B90 is usable on different make cars. Our first tool will work on base 996/986 front and rear wheel bearings (exact same bearing). This same bearing is also used on some Audi's and BMW's, so we will have to look at the design of these cars to see if the geometry permits application. For a shop working these car models, it can add a lot of productive manhours. Our ugly prototype was drawn on CAD/machined on a lathe/mill/welded AND .....the bearing pulled in less than 4 hours. Production version will be very user friendly, made from 4130 chrome moly and 52100 bearing steel, and "pretty". Best of all, it will be half the price of the B90.

Note: It is never advisable to install new bearings by applying loads "thru the balls". The installation w/the new tool applies pressure on the OD race only.


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  • 11 months later...

Here is the prototype puller with the bearing just about out. It is rough looking, but the production tool will be professional grade. This is a very robust puller, and will pull hundreds of bearings if used properly. Don't ask to see the mechanism, we will not tell you. Sorry, if you want to see how it works ...you will have to buy itBill Ryanattachicon.gifWHL BRG PULL.JPG

Did you ever finished the tool. PM send

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  • 1 month later...

We sold a bunch of the production "no suspension dismantling required" bearing tools to various DIY mechanics. But the pro mechanics did not like the fact it pulled only the smaller bearings used in the Boxsters, and 996 front wheels. So,..... we redesigned it to pull both front and rear wheel bearings of Boxsters thru 04, and 996 thru 05. Now all configurations of these cars can be serviced with one tool (regardless of FWD, RWD, S model, or base model). You can see it on Ebay with a "Porsche wheel bearing puller" search. This tool is less than half the cost of a shop replacing just one wheel bearing!

Bill Ryan

Casper Labs, Inc.

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