aluminum driveshaft "stress fractures?"

[SMP142]

so i am aware that alota ppl seem to be giving props to the aluminum driveshaft. mostly for the weight reduction. but my question is how long have you all had them on? anyone noticed any kind of stress fractures in them? b/c from my past knowledge of metals, aluminum is nice and light, also strong. but its strenth more or less has a life span when put under stress. now i have noticed you can get one-piece DS's that are steel instead of aluminum. the weight diff is like 15-16 pds instead of the 10.5 or 11 whatever it is. i am thinking that 4-5 pound increase is not all that bad considering your dropping something that already weighs 32+ pds. plus that fact that it is steel and will more than likely last longer, and be less prone to cracks. i am not sure about this but... on a hard launch a steel shaft would tend to flex a bit, therefore not being soo harsh on your drivetrain. kind of absorb some of the torque. where as aluminum is soo ridgid that its going to put all that pressure on your weakest point somewhere in the drivetrain. now i dont have an aluminum driveshaft or anything, so i do not know the quaility of their construction. but like i said from past experiance working with both materials, i just wanted to raise some questions about the two? so if anyone has a take on this (sure there will be! :biglaugh: ) then i would like to hear some opinions before i go out and do anything. -Brian

 

[Nick M]

Speaking purely on aluminum driveshafts in general, not the aftermarket product for the Supra, much of that was not accurate. Many heavy duty trucks use aluminum driveshafts becuse they are stronger. And they have a much softer hit on the driveline than steel. Ever see a bell made of aluminum? The aluminum absorbs torsional vibration much better.

In additition to the gravity difference, the drag on the engine is much lower.

 

[jetjock]

Yeah, other than the point about "aluminum" (which could mean any number of alloys with different properties) having a finite fatigue life even if kept within the elastic region while most steels do not, the rest of that is inaccurate. Not to mention torsional loading is complex and differs greatly from pure loading in shear, compression, or tension. Plus most Al alloys are nowhere near as rigid as he thinks. Suffice to say this is a complicated subject beyond the scope of one post.

It all comes down to what alloy is employed, which of the various methods was used to harden it, the type and quality of the welding process involved, and whether the engineer who designed the piece did his homework. If done right, and as long as the loads are kept within design limits, the fatigue life of an Al DS should outlast the vehicle and not transmit excessive loads elsewhere. Now the various forms of corrosion Al suffers from and their effects on structual integrity, that's an entirely different story.

 

[IJ.]

"Work Hardening"

 

[jetjock]

"Work Hardening"

Although work hardening does reduce ductility it can only occur in the plastic region ie; there must be strain. No strain, no pain

 

[IJ.]

Personally I wouldn't run a single piece shaft so for me it's a moot point !

 

[siman]

I have had mine for a year now. NO PROBLEMS.

I honestly love the way it drives compared the 2pc stock.

Going from a 45lb piece to a 13lbs piece...there is a WORLD of differnce in power transfer to the wheels. Its noticably (sp?) more responsive on the lower end and the car seems to accelerate much quicker on top end.

Of course I have a AASCO flywheel as well....but nonetheless its more power transfered!

*The ONLY downside is that VERY MINIMAL driveshaft "slack". Its a small "clunky" sound when disengauging the clutch at low speeds/gears.

-Jonathan

 

[siman]

"Work Hardening"

remember that long ( locked ) thread where me and another bloak went at it about driveshafts?

Alot of good info came out in that thread. too bad its lost:nono:

That was pre-hacked supra mania...LOL

-Jonathan

 

[SMP142]

well i am glad i am alteast getting some comments outa this thread. b/c like i said i really dunno the construction of the shafts. but atleast we are getting somewhere. it sounds like no 1 has had any problems with them. atleast not yet, which is a good thing. but just thought i would poke at some knowledge out there..... so everyone agree's the $450 is worth it in the long run?

 

[IJ.]

Brian: Well not everyone......

For me I wouldn't fit one even if it were free.

I do quite a bit of top end running so the harmonics/U-Joint eccentrics are a real issue in my case.

 

[SMP142]

so your saying its not good for high speeds? b/c honestly i am just looking for a quick street car. i am not sure at what speeds your talking about the harmonics being bad.

 

[IJ.]

I run a 4.10 diff so my shaft speed is already high so up around the sustained 130+ it would not be pretty.

 

[SMP142]

is that just b/c the allignment of it is not exactly straight? therefore a straight shaft puts stress on it your other joints? if you didnt run a single straight shaft how would you go about lightening the the stocker? or did you just get one custom built at a shop?

 

[IJ.]

Uni Joints don't let the shaft sin in perfect circles it's more like a figure eight, the longer the shaft the more pronounced this effect is.

We have a couple of production cars here that are speed limited by the factory to 180 kph for this reason.

I had my stock 2 piece modded to suit the Tremec trans and fitted all new parts to it.

 

[Nick M]

Ok, since we are going to be partially technical, it isnt aluminum. Aluminum is very light, but not strong. So it is doped, usually with magnesium. That makes it very strong. And they are also used in racing applications, in addition to heavy trucks. And they are one piece.

But, that doesnt mean the aftermarket shafts that are being sold to Supra owners that are too short are made as well.

 

[Allan_MA70]

alloy tailshafts are bad, aftermarket alloy tailshafts are typicaly shit...