After installing our engine and putting the car on the ground, we found some bad news: Our driveshaft was about two inches too short.
How could a Mustang driveshaft not fit into a Mustang? we asked.
As with most issues surrounding our Mustang’s drivetrain, the answer revolved around the Roltec transmission. This Chevy-based transmission is some 1.75 inches shorter than …
"For a bit over $1000, within a week we had our new driveshaft."
It never gets cheaper to race, does it.
One thing made of carbon fiber that can be had fairly cheaply is tubes, makes you think about chopping up a junkyard shaft and affixing a carbon tube cut to length where the steel used to be...
Edit: Looks like Robbie had similar thoughts:
I made a similar faux pas with the Datsun. In my case I'd found a driveshaft via Dave at Futofab, sadly I'd measured wrong and was off by about the same 1.75"
Fortunately I simply moved the motor and tranny back in the chassis.
"Pounds of torque"? Why not the simpler "torques"?
Is that second picture just a demo of what the old one looked like when it was too short??
I seen an aluminum drive shaft break at svra road racing event. Warren Agor's 1976 Chevy IMSA GT Monza RaceCar trailerd hundreds of miles to pacific raceway in wa state and the aluminum driveshaft lets go first time out. He was done, no fix. How much did he spend to be there and get to that race?
I suggested he not to put another aluminum drive shaft back in or it would eventually happen again after those drive shaft welds fatigue and, they will, you can't stop it from happening.
Warren Agor's 1976 Chevy IMSA GT Monza RaceCar Link >> https://raceclass.com/rpm/ads/1453/1976-chevy-imsa-gt-monza-racecar-for-sale.html
When you weld aluminum it removes all the heat treating. Your left with raw soft aluminum. it is no longer 6061 or 7075 etc unless the entire thing is baked/annealed and re-heat treated.
A drive shaft is like a huge torsion bar twisting in both directions during acceleration and deceleration. This stresses the welds repeatedly every time it twist. Remember this is aluminum? Yup aluminum has MUCH LESS fatigue strength/resistance then carbon steel.
Leave the exotic stuff to the big $$ race teams who can afford to change driveshafts like I change socks.
Here is exactly what you need at this link and it is even affordable. Check it out >> https://www.strangeengineering.net/product/3-inch-chrome-moly-driveshaft-seemless.html/
My drive shaft for my ASA stock car conversion to road race car will run a 4130 chrome moly drive shaft and those few extra lbs of weight mean I can run it for years and not worry about it breaking at just the wrong moment after I trailer the car across the country and spend a huge amount of $$ to race.
NASCAR teams do run aluminum drive lines but only once, then change them out. I can't afford that so 4130 steel it's going to be for me.
That 8 lbs extra for the steel drive shaft with that weight in a 3.5" diameter is not going to carve off a bunch of acceleration and reduce lap time and is super cheap insurance.
In reply to robert777 :
Did you even look at the aluminum driveshaft in the pics before going off on your welded aluminum driveshaft rant? Or do you have any first hand experience with quality aluminum driveshafts to know how they are actually made?... I'll give you a hint: There are no welds. 
If you refused to buy any type of part that anybody ever had fail prematurely and ended their race weekend early, you wouldn't have anything to race with... Not even a steel driveshaft.
AngryCorvair (Forum Supporter) said:"Pounds of torque"? Why not the simpler "torques"?
Paid by the letter, bro
AngryCorvair (Forum Supporter) said:"Pounds of torque"? Why not the simpler "torques"?
Because then people would complain "why not ft/lbs torque instead of torques".
AngryCorvair (Forum Supporter) said:"Pounds of torque"? Why not the simpler "torques"?
They don't hate English speakers.
I don't want to rub salt in anyone's wound - but if you twist a driveshaft apart, and you can't get a new one made in short order, you aren't trying. If you can't figure that out then pack spares.
Most legitimate 4x4/Offroad builders build custom half-shafts regularly. A half-shaft is just a short driveshaft.
Circle tracks are common around our country - someone builds driveshafts for them as well.
Someone builds truck/commercial driveshafts, too.
Are they all going to be SFI spec? Probably not. But you've got a driveshaft. And my reading of SVRA rules do not explicitly state anything about driveshaft materials or specifications.
Prior to the new car last year, the NASCAR dirve shafts were steel.
FWIW
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