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ScoobyDoo555
Barcelona


Joined: 26 Feb 2012
Posts: 1295



PostPosted: Fri Aug 02, 2019 3:28 pm    Post subject: Whining (in general) Reply with quote

And not from the owner Very Happy

I've been seeing some interesting comments about a "new-IMS-esque" scare of diff-bearings.
I saw this from deMort in a 997 thread, but it got me thinking.
deMort wrote:

Again depending on the car it can be caused by diff bearings be it front or rear


Would diff bearings create a whine on over-run, or on throttle depression?
I would have *thought* all the time, but what do I know? Very Happy

Interested Smile

Dan
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Porsche 996 Carrera 4
Mods: "new car" magic tree. Pioneer F900bt, Alpine SPG10C2 x 4, JBL GTO 804 8" subs x 2, Shiny new rads & AC! Hartech-rebuilt engine & Sports exhaust
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6981
Location: Brighton


PostPosted: Fri Aug 02, 2019 6:39 pm    Post subject: Reply with quote

I'm not sure what post i said that .. i've posted a few times Very Happy

A bearing .. let's take a wheel bearing for example .. the fault is basically a tiny knick out of the metal roller surface or possibly a ball bearing .. the surface is the norm though .. think of a small hole ..

Trust me they can be tiny and you don't get play or anything obvious to help locate this fault .

A light pressure on a ball bearing as it goes over a hole and not much happens .. put pressure on the bearing and it digs into said hole a bit more ..

its causes a noise and it will be dependant on load .. ie it will whine more on a left hand bend than on a right hand bend due to load shifting on the " hole " .

Take this as a ballpark explanation though .. im sure there are more factors at work but either way its load dependant .

A diff bearing noise .. well to me .. the load is there on acceleration and deceleration ( the bearings are at 90 degrees from a wheel bearing ) .. hence you can get a whine at these points .. get it in the sweet spot of no load .. cruising .. and the noise stops .

More common on the earlier air cooled cars .. at least that's where i see it more due to age i guess .

A front diff will also cause a noise but it's much quieter than an early gearbox shall we say .

It's never a problem as such .. it's a noise and these are annoying hence people have them repaired .

I've not seen a collapsed wheel bearing since the taper type of years ago .


Anyways .. IMHO and my way of thinking / explaining things .
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ScoobyDoo555
Barcelona


Joined: 26 Feb 2012
Posts: 1295



PostPosted: Fri Aug 02, 2019 7:59 pm    Post subject: Reply with quote

Interesting thumbsup

I'm intrigued as to what it sounds like then - is it also a serious issue (diff bearings)?

They sound like a pricey fix tbh!
_________________
Porsche 996 Carrera 4
Mods: "new car" magic tree. Pioneer F900bt, Alpine SPG10C2 x 4, JBL GTO 804 8" subs x 2, Shiny new rads & AC! Hartech-rebuilt engine & Sports exhaust
997 C2s discs. She stops quite nicely!
 
  
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wasz
Sepang


Joined: 28 Dec 2012
Posts: 2956


1999 Porsche 996 Carrera 2

PostPosted: Mon Aug 05, 2019 9:07 am    Post subject: Reply with quote

Mine started whining really bad, like a milk float.

I was convinced it was a gearbox pinion bearing or a diff bearing until I realised it was doing it with revs, not road speed.

It was my auxilliary belt pulley bearings Floor quiet at idle but whining at certain RPMs.

Fairly cheap and dead easy to swap (parts from rockauto)
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wasz
Sepang


Joined: 28 Dec 2012
Posts: 2956


1999 Porsche 996 Carrera 2

PostPosted: Mon Aug 05, 2019 9:12 am    Post subject: Reply with quote

Incidentally I got some very good quotes to rebuild the gear box from local transmission places.

Some would refuse to touch it, some thought it was an Audi box. Stay clear of those people.

The 996 box is a Getrag unit, it's pretty much the same as a Boxster "S" 6 speed. This needs a really big press and a careful operator as you only get a coupe of goes with the pinion bearing before the box is scrap.

It's the standard Boxster that has an Audi derived 5 speed, those are cheap as chips and dead easy to rebuild.

Or some have just been whacking in low mileage 997 boxes, you need to change the output flanges I think and the gear cables are on the other side but apparently they work, but the gearing is slightly different.
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