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znatale630
04-24-2008, 12:29 PM
Do you go all out and get a new carbon fiber shaft? Or is it time to pack it in and get a new car?

B518T
04-24-2008, 12:39 PM
my driveshaft went about a month and a half ago.....

a used shaft cost me 300$ and then I needed a new bearing and who knows....

so, I had an audi shop do it for 600 including parts labor and tax....

I think the 1997's had CF driveshaft....but i just stuck with stock...

gl!

317ssayzarc
04-24-2008, 12:46 PM
i think im going to need the cf driveshaft sometime soon lol, details puhleeeze!

pac1085
04-24-2008, 01:05 PM
i have a driveshaft from a 98.5 for sale. 200 bucks.

onemoremile
04-24-2008, 01:23 PM
The carbon shaft is not interchangeable and is heavier than the standard metal shaft.

pac1085
04-24-2008, 01:53 PM
The carbon shaft is not interchangeable and is heavier than the standard metal shaft.

That's not true, you can replace a metal shaft with the carbon one and vice versa...no clue why you'd want to put the carbon one in though (the carbon was superseded by the metal one in Etka) but yes it is heavier/weighs about the same.

audispeed
04-24-2008, 07:29 PM
That's not true, you can replace a metal shaft with the carbon one and vice versa...no clue why you'd want to put the carbon one in though (the carbon was superseded by the metal one in Etka) but yes it is heavier/weighs about the same.

because it is carbon ... duh

andyrew
04-24-2008, 08:11 PM
Then take some of that carbon fiber sticker and roll it over your driveshaft
Same thing, same weight, save cash.

Duh!

gotaudi
04-24-2008, 08:24 PM
The carbon drive shaft will not deform like a steel/metal one will. Metal does not do well when a torsional force is applied to it, This is another reason why aerospace companies use carbon over metal

mike-2ptzero
04-24-2008, 08:39 PM
The carbon drive shaft will not deform like a steel/metal one will. Metal does not do well when a torsional force is applied to it, This is another reason why aerospace companies use carbon over metal

Out of all the A4's that have posted about needing to get a new driveshaft I would have to say it always seems to be those with the CF driveshaft.

audiness
04-24-2008, 09:22 PM
i have to admit i dont see too many threads on here about driveshafts

pinky
04-25-2008, 08:14 AM
The carbon drive shaft will not deform like a steel/metal one will. Metal does not do well when a torsional force is applied to it, This is another reason why aerospace companies use carbon over metal


what are you talking about? metal does fine with torsional forces, which essentially boils down to a shear stress..

if the driveshaft really is carbon fiber composite, steel may be stronger, depending on how the fibers are oriented in relation to the applied loads..

cf is used in aerospace for different reasons.. it doesnt corrode, high strength-to-weight ratio, withstands high temperatures, etc... i wouldnt exactly say its redeeming factor is shear strength..

onemoremile
04-25-2008, 08:19 AM
The carbon drive shaft will not deform like a steel/metal one will. Metal does not do well when a torsional force is applied to it, This is another reason why aerospace companies use carbon over metal

You're comparing apple sauce to orange juice. Aerospace has nothing to do with this and no reasonable comparison can be made.

The reason the carbon shafts are heavier is the way carbon fails. Since carbon has a catastrophic failure mode it tends to be overbuilt. That makes it much stronger than aluminum or steel but also heavier and still much easier to damage. I've designed racing bike parts in carbon, steel, and aluminum and broken two of the three. Steel just doesn't break like the other two.

gotaudi
04-25-2008, 08:23 AM
what are you talking about? metal does fine with torsional forces, which essentially boils down to a shear stress..

if the driveshaft really is carbon fiber composite, steel may be stronger, depending on how the fibers are oriented in relation to the applied loads..

cf is used in aerospace for different reasons.. it doesnt corrode, high strength-to-weight ratio, withstands high temperatures, etc... i wouldnt exactly say its redeeming factor is shear strength..

Simple fact, carbon has a higher yield strength in a tensile state. If you design a drive shaft you are going to orientate the carbon fibers accordingly. In conjunction carbon fiber also dampens quite well when strain is applied. where as in a steel drive shaft the strain is not dampened as effectively leaving you with a better transition of power.

onemoremile
04-25-2008, 08:25 AM
Carbon also fails in a "soft" fashion. Rather than a broken driveshaft beating the floorpan to death you get a nice soft broom that sweeps under the car. The problem is that the resins are what keep carbon together. A gouge or deep scratch is enough to cause massive failure.

pinky
04-25-2008, 08:33 AM
well i mean obviously the fibers are going to be oriented to maximize their strength.. with a driveshaft you're going to know how (direction and approx. magnitude) of the applied load...


onemoremile makes a good point.. one of the main reasons steel is widely used in these kinds of applications (as well as structures) is that it has high ductility

as for the material damping properties of carbon fiber.. this would only be realized in dynamic loading situations (ie cyclic loading), not constant applied forces.. material damping doesnt really affect constant loading.

gotaudi
04-25-2008, 11:39 AM
well i mean obviously the fibers are going to be oriented to maximize their strength.. with a driveshaft you're going to know how (direction and approx. magnitude) of the applied load...


onemoremile makes a good point.. one of the main reasons steel is widely used in these kinds of applications (as well as structures) is that it has high ductility

as for the material damping properties of carbon fiber.. this would only be realized in dynamic loading situations (ie cyclic loading), not constant applied forces.. material damping doesnt really affect constant loading.


The loading is differential. Their is nothing constant about the way an engine makes power.

pinky
04-25-2008, 01:12 PM
you're right, but there is also inertial damping from the flywheel and all of the other spinning parts that have some finite mass.

material damping is typically negligible.. i cant believe i'm even discussing whether the difference in material damping between steel and cf is going to actually make some sort of noticable effect.