stupid drive shaft. whats better steal or alumn

[jdub]

LOL...yeah it is
If I were to be doing hard drag type launches on a regular basis, steel would be my choice.

For what I do, a MMC material would be optimum...something like the aluminium boron carbide matrix Ford uses on some of it's drive shafts. Critical speed jumps for my specs to 14,238 RPM for MMC

 

[IJ.]

Exactly Ian...each situation, tranny/differential/tire configuration, and use of the car is unique. If you go with a one piece, it absolutely must be balanced perfectly...the shop that makes it better be good. Safety loops are a very good idea. The problem with the stock two piece is the dual tube, bonded rear section...if it's twisted up, the shaft is no longer in phase and can cause torsional issues during power transfer. The two piece design is not as dependent on balance and affords a greater safety margin for sure, but the speeds we're talking about is well above 150 MPH on stock tranny/differential components. Not too many folks sustain these kind of speeds on a regular (or if ever) basis.

Material wise, steel is not necessarily "stronger", it has a higher modulus of elasticity allowing flex to the torque applied. The cost is the greater tube weight...3 times what you get with aluminum. Critical speed increases to 12,788 RPM using a steel tube...not a huge benefit when you consider the NVH aspects of using steel. Saying aluminum is limited to xxx HP is completely wrong.

The decision to go 1 or 2 piece needs to be thought through...just giving the OP the tools to do this.

Been nagging about this since I first came to SM back before we lost everything to a hack in 2003....

Probably the single biggest reason that people Dog the 2 piece.

Aluminium/Work Hardening/Pass

 

[jdub]

The degree work hardening will have a significant effect is going to depend if the material shape (in this case a shaft) is twisted to the point where dislocations occur in the stress field resulting in rearrangement of the metallic crystal lattice. Translation: it's going to depend on the torque applied and how much.

Fortunately, bending moments produce the largest and most localized stress fields. Twisting moments distribute the force along the length of the shaft...the material will actually become stronger, but also less ductile. Translation: the shaft will eventually become brittle.

All metals work harden, steel is one of the most susceptible...the difference between it and aluminum (in this case) the modulus of elasticity is 3 times greater than aluminum. The twisting moment is a huge factor in reducing the chance of failure due to work hardening. The distribution along the shaft make it highly unlikely any one area will become brittle enough to fail. All bets are off though if the welds attaching the uni-joints are crap.

The more torque, the more stress fields form, the faster work hardening takes place. Keep in mind that aluminum and steel have similar torsional yields...work hardening becomes more of an issue as these yield limits are approached (plastic region). Based on the ability of "most" mod'ed 7M's to produce torque in the 300-350 range, you are at the bottom end of both aluminum's and steel's yield strength. It would take a very long time (considering distribution along the shaft) for a one piece to reach the failure point. High HP/torque, hard launches...different story.

 

[webbs7mgte]

this is great info i love everyones inputs there is no declared winner in this battle and never is. you really have to run both and see whqat your own opinnion is. im thinking possible STICKY material

 

[bmoss85]

would having the one piece shaft cryo treated have any beneficial affect?

 

[IJ.]

Can't hurt
(I had my 2 piece done)

 

[Orion ZyGarian]

Definitely an excellent thread filled with experience, science, and logical thinking. This is why I still come to SM; people here have been sorted out between the casual car guys who mod and the experienced people who know what they are doing. Thanks guys, this information is invaluable.

 

[jdub]

The answer to the question one or two piece DS is "it depends"...same for the material used in constructing the shaft. Just like IJ said it's not that a failure of a one piece WILL happen due to the various factors, I'll turn it around and say it's very possible it WON'T happen either. Defects in material, crappy welds, poor balance, etc makes failure of a one piece more likely due to it's length....the opposite is true for a well made shaft too.

You must consider the intended use of the car and how much torque you produce...access the risk and make a decision based on your comfort level. It's not about opinion, it's all about looking at the facts and making an informed choice.

 

[bmoss85]

Im just wondering how a carbon fibre ds compares to aluminum or steel. does anybody know?

 

[IJ.]

Carbon's critical speed is through the roof and the only way you'll exceed it with a Mk3 is by strapping it to the space shuttle.

Another "bonus" is that if they fail they turn into a broom and sweep the road and DS Tunnel and don't tear the car to bits.

 

[Poodles]

They aren't as impact resistant, and a nick in them will cause a failure (think strong but fragile).

After seeing that one guy with the Crown have a 1-piece driveshaft failure, I won't go near em...

 

[bmoss85]

yeah i was wondering how a carbon shaft would do with taking hits from debree on the road. there's no way you could keep small rocks and what not from hitting the ds.

EDIT: does anybody know what the titan carbon ds weighs?

 

[1jzSpecial]

Don't know if this a myth or not, But is it true you loose a bit of torque when upgrading to Aluminum or steel DS?

 

[gtimportfanatic]

i heard it feels as if u gain some.. the car is easier to move from a standstill..

 

[EdT.Mk3]

^
I believe the feeling of having it was the same as, "Having some fat people get out of your car."