Alum. Drive Shaft & 1/2 shafts

Per title- anyone using aluminum drive shaft & half shafts? would like the feedback; weight savings, driving improvement, pitfalls etc. thanx

I had a problem when I used a 3" aluminum driveshaft. Under hard turns, the body shifted and rubbed the driveshaft. Didn't have a problem at first when I was running poly body mounts, but when I switched back to rubber mounts the clearances were so tight that it created several rub locations along the shaft. I ended up switching back to a smaller high quality steel shaft.

When I made an enquiry to an alloy driveshaft manufacturer he ran my dimensions and said "don't bother". Granted this was on a much smaller driveshaft (in the Triumph racer) but I was rather surprised by his honesty.:bounce:

i'm using a C4 aluminum driveshaft i picked up for $50 on ebay. I think it came out of a manual C4 car to fit my 700r4 transmission.

The steel driveshaft made a scarey drone when it hit 5500 rpm. The aluminum makes no sound all the way up to 9000 rpm.

how much weight savings over the steel d.s.? I have a muncie trans., so not sure about the u.joint & length... But, I like the cost effective opportunity!

rodeck350 said:

i'm using a C4 aluminum driveshaft i picked up for $50 on ebay. I think it came out of a manual C4 car to fit my 700r4 transmission.

The steel driveshaft made a scarey drone when it hit 5500 rpm. The aluminum makes no sound all the way up to 9000 rpm.

Click to expand...

What you got that spins to 9 grand?

SmokinBBC said:

rodeck350 said:

i'm using a C4 aluminum driveshaft i picked up for $50 on ebay. I think it came out of a manual C4 car to fit my 700r4 transmission.

The steel driveshaft made a scarey drone when it hit 5500 rpm. The aluminum makes no sound all the way up to 9000 rpm.

Click to expand...

What you got that spins to 9 grand?

Click to expand...

POS goodwrench engine turning 6300 rpm wound out on the straight at Mosport.

700r4 final 0.7 to 1

4.56 gears

6300/0.7 = 9000

about 90 mph flat out:clap:


Acutally it calcs out to 150 mph but i don't know if i believe that.

mrvette with the top down yes. me probably not.

Do the C4 halfshafts use the same u-joints as the C3? Could those be shortened to fit?

I have aluminum half shafts and drive shaft in my car (uses a C-3 differential with C-4 outer bearing carriers). To answer the question above, yes, the C-4 u-joints are the same as a C-3 and yes, the half shafts can be shortened to fit. Reno Racing in Mesa Arizona has done several sets of them. I had the Driveshaft Shop build mine -- 6061 aluminum with billet ends and heavy duty 1350 u-joints. The only issue I have found is that you must be very careful when you jack the car and let the suspension go full droop. If you rotate the wheels, the u-joints may "bind" at the extreme angles. One advantage of the aluminum shafts is a reduction in "rotating mass", not just the reduction in static weight. It is like going to a lighter flywheel or clutch.

Pappy

If your driveshaft is turning 9000 rpm, it does calc to ~153 mph with 26" diameter tires and a 4.56 rear end, BUT, if you saw only about 90 mph, your tach is likely incorrect. I'm more inclined to believe your speedo than the tach.

As far as drive shaft critical rpm, the stock steel 2" diameter, ~30" long corvette shaft is safe to over 10,000 rpm, primarily due to its short length.

For additional information on critical speeds, try this link:
http://www.markwilliams.com/driveshafttech.aspx

For a calculator to determine the critical rpm of your driveshaft and see what difference a material, length, and/or diameter can do:
http://www.pontiacracing.net/driveshaftspeed.htm

vette427sbc said:

Do the C4 halfshafts use the same u-joints as the C3? Could those be shortened to fit?

Click to expand...

yes and no. The heavy duty diff with T400 uses 1330 u joints (maybe there are exceptions but that's what i had originally anyway) which are bigger. The light duty rear use 1310 which is what the C4 shaft had.

I'm sorry, i'm thinking driveshaft. Halfshafts depend on year. The iron diffs use 1350s the aluminum use 1330s i believe.

larrywalk said:

If your driveshaft is turning 9000 rpm, it does calc to ~153 mph with 26" diameter tires and a 4.56 rear end, BUT, if you saw only about 90 mph, your tach is likely incorrect. I'm more inclined to believe your speedo than the tach.

Click to expand...

I'm just kidding about the 90mph. I'm guessing 135. I don't think i have enough HP to go 150 so the tach is probably off. The speedo is still calibrated for a 3.08 so it wrapped all the way around to the bottom. I don't make a habit of looking down a lot at that speed.

That is some good info in the links. I suspected the steel shaft was going to destroy itself so i never maxed out with it. It probably wasn't balanced correctly after being shortened. It sounded really bad like there were some compounding harmonics going on. I think i'm still pushing the C4 shaft to its limits. I think its a 2.5 inch.

That 4.56 gets pretty hot turning a steady 5000 rpm at highway speed for hours at a time. I bet the bearings are pretty fried.

GT6Steve said:

When I made an enquiry to an alloy driveshaft manufacturer he ran my dimensions and said "don't bother". Granted this was on a much smaller driveshaft (in the Triumph racer) but I was rather surprised by his honesty.:bounce:

Click to expand...

I respect the guy's honesty. There's a legitimate reason for his comment, but a lot of guys would rather take your money than tell the truth. When substituting an aluminum shaft for a steel shaft remember the inertial effects of the tubing diameter. The C3 driveshaft diameter is pretty small (perhaps 2 inches), while an aluminum replacement would probably be around three inches to retain the same strength. The moment of inertia (resistance to rotational acceleration) varies as the radius squared. Unless the weight reduction of the aluminum shaft is greater than the radius ratio squared, then it's a losing proposition regarding acceleration (or deceleration) of the shaft. On the up side though, steady state cornering/handling should be enhanced by the reduction in vehicle weight or partial reductions in unsprung weight.

Thank You for the succinct summary. Excellent. I wish I could talk like that:confused2:

It was just such a tradeoff that queered the deal in my application.

I'm always looking to save an ounce on sprung weight but this one just didn't factor out.

a bigger "bank for the buck" would be a smaller and lighter clutch/flywheel and second on my list would be an EDM lightened ring gear for your diff. aluminum driveshaft and/or halfshafts are so close to your centerline I would doubt anyone could tell the difference.

In terms of rotating mass, wouldnt you notice a 2 or 3lb difference with alu. halfshafts compared to a lightened ring gear (I dont know how much lighter the EDM one is, guessing a lb or two)? The ring gear sounds far more expensive too...

How much could I expect to pay to have two C4 shafts shortened?

Since energy absorption is a function of the inertia times the rotational velocity squared, a 30 lb flywheel has roughly 30 times the rotational inertia of a 3" diameter half shaft; further the ratio of rotational speeds is 4.11:1 in high gear, so the energy absorption of the flywheel would be ~30 x 4.11 squared or approximately 500 times greater of one half shaft, or 250 times greater than both half shafts. If you cut the flywheel to half the weight, its effect would drop to only 125 times greater than the half shafts.

Keeping a light 15 lb flywheel, let's compute the flywheel's energy absorption while in first gear (2.20:1)... Therefore, we'd have 15 x 4.11 squared x 2.20 squared, this computes to 1,226 times one half shaft; or 512 times greater than both half shafts.

Redvetracr is right about the flywheel making a bigger "bank for the buck", but because of the rotational velocities squared, a lightened ring gear is an order of magnitude less effective.

larrywalk said:

Since energy absorption is a function of the inertia times the rotational velocity squared, a 30 lb flywheel has roughly 30 times the rotational inertia of a 3" diameter half shaft; further the ratio of rotational speeds is 4.11:1 in high gear, so the energy absorption of the flywheel would be ~30 x 4.11 squared or approximately 500 times greater of one half shaft, or 250 times greater than both half shafts. If you cut the flywheel to half the weight, its effect would drop to only 125 times greater than the half shafts.

Keeping a light 15 lb flywheel, let's compute the flywheel's energy absorption while in first gear (2.20:1)... Therefore, we'd have 15 x 4.11 squared x 2.20 squared, this computes to 1,226 times one half shaft; or 512 times greater than both half shafts.

Redvetracr is right about the flywheel making a bigger "bank for the buck", but because of the rotational velocities squared, a lightened ring gear is an order of magnitude less effective.

Click to expand...

I'm just enough of a geek to enjoy it when someone does the math on these things. :thumbs:

I want to thank everyone who contributed on this; great example of member support. I won't lose sleep over the orignal consideration. FWIW, I have a billet flywheel that was 25 lb.s, (resurfaced 2x) I noticed that most of the weight savings was on the outer area, as the machining process relieved the thickness on the backside outer circumference. To continue the discussion. With a 4sp. manual transmission in mind; would the aluminum drive parts absorb some of the "hit" and facilitate a longer life for the drive train parts?

Don't overlook the fact that 50% of the halfshaft weight is unsprung weight, and ANY reduction of unsprung weight is a good thing (if your concern is handling). Also, I don't consider reduced flywheel/clutch weight and reduced driveshaft/halfshaft weight to be an "either/or" situation. If you have already gone to the lightest flywheel/clutch weight you can stand/afford, why not look at other places to reduce total and rotational weight? In my case, I needed a custom length halfshaft (longer than a C-3, shorter than a C-4), so I went with the lightest I could find that would still handle lots of torque. All things being equal, a larger diameter tube is stronger in torsion than a smaller tube. As far as reducing driveline shock loading with aluminum tubes, I doubt you will get much benefit, but I have heard that there is some "cushioning" with carbon fiber tubes -- can you spell expensive?

Do aluminum shafts (C4 specifically) have the strength needed to act as a suspension member though? Seems like they can handle the torque from high power C4's, but I dont know about compression loads. The Denny's aluminum shafts for C3's are probably thicker walled and use a higher quality aluminum, but are also probably twice the cost of what you could have some used C4 shafts cut to length for.