Aluminum drive shafted
 

Back around 2009 I picked up an aluminum drive shaft off a Pontiac Firebird with the super rare 1LE and WS6 preformance packages off ebay for the going rate.
I didn't know the condition of the drive shaft or universal joints. So I took it to tractor trailer machine shop in Virginia Beach when I was living out there that specializes in drive shafts to replace the universal joints and ballance it. I think that was 2010. I finally put it in its new home.
I had kind of forgot about it until a friend needed a drive shaft for their camaro when one of the U-joints started clicking, I sold them the steel one out from under my firebird for cheap and went to go dig out my aluminum drive shaft from where it was hidden some where in the garage. Turns out it was in the shed.
The weight difference is 4 pounds, yes of course I weighed them.
I departed from sealed U-joints and opted for greasable ones, since all U-joint failures I know of involved the grease running out of the sealed U-joints over time and one of them burning up. And they tend to fail at high speeds when they do fail.
Total price was nearly $300. $140 for the shaft plus shipping and the bill from the machine shop was $155.

Results? Besides weight loss.

Seems to be missing a slight vibration at higher speeds that I thought was a tiny tire imbalance.

4lbs of unsprung weight is nothing to scoff at. I'm not sure if there will be efficiency gains, but acceleration from low speeds is probably noticeable on the 'butt dyno'.

Any better MPGs?

Why would a driveshaft be unsprung weight? Maybe semi-sprung, if the car has a solid rear axle instead of independent suspension.

Well sorry I commented.

Nice! Cool car, I always liked that generation of Firebirds. Very muscular styling. Almost had one installed on my Mistang way back when, but we decided it probably wasn't worth it. The body structure was so floppy that the smoothness gains would be thoroughly outplayed, and it was built up as a show-quality cruiser, not a fast car.

Don't feed trolls [he sez], push back. You meant 'reciprocating mass' not 'unsprung weight'.

Perfectly understandable. To err is...Hue-mon?

Well, the end attached to the axle IS unsprung weight.