FYI ; My '06 Power Wagon has AL shaft.
It's also speed limited around 90-95MPH electronically.
The critical speed mentioned has to due with harmonic resonance, which has many factors, length, stifness of shaft material, weight, rotational speed, etc.
You could also look into a custom Carbon Fiber shaft. They are extremely stiff and lighter than AL.

 

Notice both of yall have 4x4's lol

 

Yep. Amazing how much science goes into a section of spinning steel or aluminum and then the critical speed number is only theoretical and not actual due to impurities, manufacturing erros, tensile strencth of the metal used and on and on. Well, it's only theoretical until you actually hit a shaft's critical speed then it becomes very realistic!

I'm still uneasy of carbon fiber. Yeah I know it's used all of the time in high performance applications and carbon fiber is extremely strong but, the ends are still only glued on and that's what gets me.

I'm going to design a 4 1/2" diameter shaft with a wall thickness of .125 6061 aluminum. This should put critical speed upwards of 5000-5500. If not, I will be buying the SRT-10 two piece shaft or an earlier Dodge two-piece shaft and having it fitted to the truck professionally.

I'm way ahead of the game on this one. This will not happen again. Been putting the old engineering think-cap on......
I actually have an email into Dodge right now to see what other factory options might be available since dealerships are no help at all. I'm sure I'll get the old "it's proprietary information or otherwise unknown" answer they seem to be good at giving.

 

I have a 1997 Dodge 1500 Extended Cab 2 Wheel Drive V8 5.9 Magnum and I also have an aluminum driveshaft or should I say HAD an aluminum driveshaft. I was 5 hours away from home when POP there it goes simply broke in half. I am having a very difficult time finding a replacement driveshaft. Any Suggestions. I do not even know if this is a single peice or a 2 peice shaft.Because everything I look up calls for a two peice BUT there is no where to mount a two peice under this truck. So I am confused. But as a Single Mom I never claimed to be an auto mechanic either lol.

 

my 04 has an aluminum shaft...magnet dont stick

 

Contact a drive line shop and have them rebuild it. More than likely it was a one piece or you would see the carrier bearing under the truck. It's just a big loop of steel.

Or just get rid of it and get a Shelby. I did!!

Of course the Shelby looks funny trying to tow a 28' camper......

 

Mine is an 03 QC 4x4 and I haven't checked the driveshaft.... .... yet.
But I have 3.92 gears and I do get a vibration at 170kph (105mph) but I just thought this was the governor and backed off. When the governor kicks in is it just a smooth cut out or does it make a vibration?
My buddy's got an 05 Daytona 2wd and he says the same thing.
I had many U joints fail on my old Cordoba 440, steel shaft but smaller diameter which makes for a lower centrifugal force at the same rpm. The U joints were always at fault and failed in 1-2 shifts always. Lucky for me, when the front one broke, I had an H-pipe exhaustand it just bounced around in the tunnel.

 

This is a valuable post.
Thanks to all who have provided information,
and the pictures 'are worth a 1000 words'.

People considering getting 4.56 and 4.88 differential gears should read this post, and pay attention that a gear swap has many 'devil in the details' and that a steel driveshaft is also called for.

It is not just the 'critical speed' of the driveshaft.

The differing number of gear teeth on pinion and ring gears with the numerically high ratio gears like 4.10, 4.56 and 4.88 set up a 'chatter'
vibration that can build into a resonance. (This is the same kind of science as leads to 'drone' of a muffler at highway speeds, and why a church organ has so many different length pipes to make music)

 

Steel shafts willbe better than Aluminum for rock crawling or doing 60ft. burnouts, but not likely better for high speed.
A lighter, stiffer Aluminum shaft is better for high (rotational) speed due to the higher critical speed a properly designed AL shaft will have compared to asamelength steel one.

A steel shaft thathas a bad high speed harmonic isn't likly to snap in half like an AL, but the u-joints are going to fail eventually...
I'd rather have an Al shaft flailing around under my car/truck than a steel one.

 

Anybody check out the 06 Mega cab 4x4 shaft ? Just want to be sure ... I tow a 27' trailer and want to ensure that my little ladies are safe. Cant check mine right now. Its in the shop. Put a little fender bender on her thats getting taken care of .....