Stock driveshaft weight, and the benefits of aluminum
 

What is the stock weight for an NA driveshaft? Has anyone here had a custom lighter one made?

What kind of reduction in drivetrain loss can be had with say... even just 5lbs shaved off the driveshaft? Just for example.

They're pretty light, less than 15 lbs, maybe even 10 (edit, quick search shows 11lbs)... most of the weight is at the ends, u joints and slip yoke. If it isn't aluminum already I can't imagine you'd save more than a lb or 2 going to aluminum.

miataroadster.com makes a carbon fiber drive shaft

http://miataroadster.com/store/produ...erm=driveshaft

Can't find it.

I think he stopped offering them after only selling one in 5 years. You may want to send him an email if you are serious about it.

I'm not serious at all about it, I just wanted to see how much weight it saved.

Not much or at all IIRC, because the joints were so much beefier.

Well, that would be it. Anyone heard of Miata drive shafts breaking?

Lightening the flywheel and wheels is money better spent. The driveshaft, even if it were heavy, has its mass very close to its center.

Better spent, yes. One could argue that money on a lightweight flywheel is better spent on a turbo, or that turbo money is better spent on track days, or that track days would be better put into savings or that savings would be better put into investments...

But I was curious about driveshafts.

Right, sure. But the whole idea is to reduce rotational mass/moment of inertia. I'm just saying, if you're willing to go as far as lightening the driveshaft, you're doing yourself a disservice if you aren't already using the lightest flywheel/clutch and wheels that you can.

Yep, I'm currently using a 1.6l 7lb flywheel and will move to a 949 twin disk. I understand. :)

Never heard of one breaking and I searched m.net and found nothing.

I have done everything else to lighten the rest of the drivetrain. Flywheel/clutch, 13'' Panasports (8.2lbs each). Just thought out of curiosity sake to see what the driveshaft would net. Coming from FD's it's a fairly popular mod to have a lighter alum dshaft made.

Since the difference would be minimal, I'm obviously not going to do it.

well unfortunately not ALL of us can afford a 949 twin disc. I'm happy with my 9lb flywheel and FM2 for now.

I've bought two miata's cheap (one for 1700, the other for 1750) with mint hardtops (and one in pretty decent condition) becaue the front u-joint broke on the driveshaft.

The driveshafts didn't fail because of high torque, they were both bone stock 1.6s. They failed because the bearings in the U-Joint degraded over 20 years of use. The first one lost the U-Joint, but the driveshaft didnt completely come apart, though it completely DEMOLISHED the rear section of the transmission case. The second driveshaft broke cleanly off at the u-joint and fell between the PPF and Exhaust without additional catastrophic failure. The front yoke remained in the tail of the transmission for a short period of time. When I went and looked at the car, the guy said it was driving and just quit a block from his house - engine ran fine, transmission shifted fine, but the car wouldn't move. I suggested that it could have been the driveshaft u-joint, then got on my hands and knees and looked under the car to see the front yoke of the driveshaft laying on the ground where it had fallen after surely spinning vainfully long enough to vibrate itself out of the transmission. I replaced the driveshaft in my built car after a cross country trip long before owning either of those two cars because the front u-joint
was making death threats to my car.


BUT....None of those failures were actually power related.

Mine has 230k on it, and is 15 years old. Damn shame they are not serviceable.

I try to change the U joints on my other vehicles every 50k, and even at that point they're starting to get worn enough to get stiff. A driveshaft shop once quoted me 900$ to make a CF one and I almost considered it just so I could replace joints. If I could find an aluminum one with replaceable joints for under 300$ I'd buy it, I'm planning on going back there some time to see if they'd seriously make me an aluminum for the Miata for a reasonable price. (They normally are making custom driveshafts for big trucks or trains or whatever people use massive driveshafts for, so I don't even know if their carbon fiber offer was serious)

You can have Miata driveshafts rebuilt stronger at a local shop should you feel the need. It's not very expensive to do so. Around 100 in NC.

Change u-joints every 50k? Are most of your cars from the 1950's? I've never heard of a Miata joint going bad. Until now. On the 200k mile cars, they've all been intact that I've seen.