Aluminum driveshaft ? {merged 11-8] drive shaft shafts

[GRNDSM]

I am revisiting different driveshaft options, because I am trying to piece together parts for my Spyder AWD conversion. My original thinking was going with a one piece, CF driveshaft, thus eliminating the need to weld-in AWD carrier bearing supports. Great idea? Perhaps… if you have $2k burning a hole in your pocket… But then I found this thread and it reminded me of something:

Last few years I have been driving and tuning my friend Bruce’s black 92 Talon. It is a fairly quick car (consistent low 10’s/high 9’s), while still being in DS Eliminator Class (still has exhaust and interior). Back in ’07 or so, Bruce decided to treat himself to a DSS aluminum driveshaft. As he put it, “There is nothing else to do in off-season, so I will get this nice, but not necessary mod”.

I had my reservations, but hey, that is his car… As you can see from the photos, it is a gorgeous piece! I can’t blame anyone for wanting something this pretty on their car. The shaft worked fine, until we broke a transfer case. No big deal, this happens fairly often on fast DSMs, right? That is why we always bring a spare. But we found that the yoke was twisted (it was evident looking at the splines) and we were not able to insert it into the new transfer case. Our day of racing was over and Bruce had to buy a new yoke (~$100, as I recall).

After installing a new yoke, Bruce also invested into a driveshaft loop. But on the first pass the u-joint came apart (probably due to improper install job) causing the aluminum driveshaft to get banged up with-in the safety loop. Another racing day is over.

DSS said that the shaft was beyond repair and that the best they could do is give $100 off a new one. There was less damage to the shaft before we installed the driveshaft loop! This is when thin wall aluminum is NOT your friend… They will not be damaged beyond repair every time, but you do have to expect this happening occasionally.

That is when I had enough and insisted that Bruce’s goes back to a stock driveshaft. He did it and the car has been fine ever since! We might have broken another transfer case, but we always have a space transfer case and an OEM driveshaft on hand!

I can’t fault DSS for anything in this experience. But I do consider this product unnecessary! If you still want to get it, make sure at the very minimum invest into a spare DSS yoke! Or, if you really value your race days, you might want to consider a spare driveshaft.

As for the entire pound per pound comparison, what really matters the moment of inertia of where you actually save the mass. And that is a function of a diameter of where you see weight reduction. Since stock driveshaft is only 2” in diameter (or so), going to a 3” or even 4” aluminum driveshaft reduces the effectiveness of such weight savings. A flywheel analogy does not work! First of all, you are reducing a lot more weight (going from 20 to 10 lbs), second, you are doing this weight reduction at approximately 10-12” diameter, which is very significant!

Bottom line, anyone who reports “feeling the difference”, is experiencing a placebo effected brought upon by the fact that they just spent $700 on something they didn’t need. Or they had some major slop in their original driveshaft components due to wear.

Back to my original problem, I think that I will weld-in those carrier bearing supports and go with an OEM driveshaft . I do not want to create unnecessary problems.

 

[twicks69]

Thanks for the updated information! I never really cared for the DSS design. I was hoping that the Shaft Master's design for the 2G was a better product as well. So, I guess I will make my own.

I am putting a stock driveshaft back into the car when I get it running again, and I am in the process of designing a 2-piece custom driveshaft for my car. It will consist of 3.5" chromoly driveshaft with 1350 solid joints, and a Moser forged 29-spline input yoke with a custom carrier bearing and Lobro joint, along with a custom rear diff flange, and a custom transfer case. I will end up welding in larger mounts to accept the driveshaft, and 2 loops.

It is a bit overkill for most cars, but I am at the last pieces of the drivetrain puzzle currently. The rear end/driveline will be more than competent, and the transmission is more than competent, leaving me with the transfer case and driveshaft.

Up until April, the entire rear end, axles, driveshaft, transfer case, subframe and bushings, rear diff bushings, rear diff cover, etc. were all stock original parts that were never broken. The driveshaft carrier bearings were still pretty decent as well.

When I broke the rear diff cover, it took out my driveshaft, axles and subframe in the back. Unfortunately, like most DSM's, breaking one part turned into replacing half the car.

The stock driveshaft is fine for quite a bit of abuse and power, BUT, it will only last so long before breaking a U-joint connection or twisting the input yoke splines from extremely abusive launches found on drag radials, or sub-1.5-second 60's on good tires.

Never had a problem with mine until sub-1.50-second 60's, and most people here have seen the video from that.... Unfortunately, I feel that most of the problems with my scenario could have been alleviated from running the plate-steel rear diff cover from Andrew Kisner (frontline fabrications), as it looked like my cover was cracked due to oil seepage around the upper portion of the flange. When the rear diff cover broke off the upper tabs, it cart-wheeled the diff, taking out the axles and driveshaft at the same time. It also destroyed the subframe mounts.

Lesson learned. Either keep-it-simple-stupid (KISS), or go-big or go-home.

I kept it KISS for many years without problems. Now, I have to go-big or go-home to reach my goals of 8-second passes.

 

[GRNDSM]

BTW, Bruce's cars runs consistant low 1.4's, with best of 1.39 60' times. Naturally, that
is on full slicks.

 

[bmoha2]

Steel is real. I applaud your decision to run cro moly tubing. Superior strength than aluminum or stock steel. Lighter weight. The modulus of elasticity of cro moly is higher than that of steel. Will take alot more before it permanently deforms and it's lighter weight. I'd take a cro moly driveshaft over steel, aluminum or cf any day. And it shouldn't be ridiculously expensive. My bro in law does a lot of extreme rock crawling and mudding. I think almost everything you need can be ordered right out of 4 wheeler magazines. Serious off roaders have been fanning up their own driveshafts etc for decades.

 

[twicks69]

Steel is real. I applaud your decision to run cro moly tubing. Superior strength than aluminum or stock steel. Lighter weight. The modulus of elasticity of cro moly is higher than that of steel. Will take alot more before it permanently deforms and it's lighter weight. I'd take a cro moly driveshaft over steel, aluminum or cf any day. And it shouldn't be ridiculously expensive. My bro in law does a lot of extreme rock crawling and mudding. I think almost everything you need can be ordered right out of 4 wheeler magazines. Serious off roaders have been fanning up their own driveshafts etc for decades.

Yeah, the goal is to have it around the $800-900 range for both shafts, forged input yoke, custom carrier bearing and custom lobro bearing assembly, including U-joints.

The rear diff flange will be a one-off lathed piece, so that will likely be a bit more expensive for the initial piece.

As well, the transfer case will require substantial machinework to fit the large output shaft I will be running -- it is larger than every other one on the market for our vehicles.


I am just not a fan of aluminum driveshafts, the associated harmonics, and the inherent flaws in the structural design utilizing aluminum for the base material. Chromoly will be better in my application.