Driveshaft question. Good or bad idea?
 

Im just wondering if this is a good way to save a buck.

When I had a driveshaft made for my Firebird a few years ago it was about $400.

Couple years later I had it shortened and a different end put on it. It was $100 with a nice solid U joint.

I see modern RWD truck driveshafts for cheap on FB Marketplace locally all the time. There is actually a 4" aluminum one that would probably be like $600 if I ordered it new for $80.

Is there any reason not to find a cheap OE driveshaft and have a local shop shorten it and put ends on it? Saving probably 50% over ordering a custom shaft?

I just look at this as the equivalent of running a lincoln fan instead of a $400 Derale unit.

Damn... good question. I can't see the problem with this, but my opinion doesn't mean much. It *seems* like a great idea.

Just curious - why are people selling these driveshafts? Seems like an odd part to be slinging on Craigslist.

You see a ton of jeep ones, but they arent the right type. But I was thinking this would be an easy pick a part piece too. So IF it is indeed a good idea, I would imagine there is plenty of supply.

The one I referenced for $80 I actually dont think is OE. I think dude had it made for his race truck and sold the truck or something. But still, just doing a search for the tube and then taking it to have the ends installed and balanced seems a money saver.

I don't know about the other manufacturers but the GM truck aluminum driveshafts rot from the inside causing failure. If you are racing, that can be very dangerous. Just go get a Denny's shaft made.

Wouldnt you be able to inspect for that though when you cut the ends off? You would have bought a turd and have to start over, but it should prevent installing said turd.

Im also not sure all the OEMs currently use aluminum. I might have a little more faith in steel.

I dont necessarily have any plans for this anyway, Im just brainstorming.

A lot depends on the operation you're going to put the shaft under. Build construction, diameter, length all play a factor in what a driveshaft will be able to withstand. Remember, you're not just worried about what the driveshaft will withstand from say a drag launch, but what it'll cope with at speed.

Here's your GM truck shaft exploding on the dyno. https://www.youtube.com/watch?v=M8Kjuk6KXMA

If you're doing this to put in your cruiser that doesn't see high speeds at the end of a drag strip, it might be a way to get something in there a bit cheaper.

On a performance build that might be raced, I wouldn't touch it.

Do you have a shop that welds aluminum shafts available?

.....I believe we get our "FAST" carbon fiber driveshafts for ~$400 for the dirt late model.

Did you ask your driveshaft shop how much to make you a shaft instead of modify?

Here's just one of many lawsuits regarding aluminum GM driveshafts on vehicles far from anything but a cruiser > https://gmauthority.com/blog/2019/12...on-driveshaft/

There is nothing wrong with an aluminum driveshaft built by a competent source.

I learned my lesson twice about driveshafts. Lesson one snapped a factory cast input shaft. Lesson 2 ..I had a local shop build a 3.5 inch steel shaft with a 1350 spicer input shaft and a conversion u joint on rear...driveshaft had limited clearance where the transmission tunnel narrowed hated the damn thing. Finally did what I should have did years before Chrome moly input ,1350 u joints Chrome moly 3 inch driveshaft and chrome moly diff input..Would have been cheaper and easier on parts doing it right first..plus the Strange shaft with all the goodies is in my eyes a good value for the money. Oh and cheaping out first also cracked the transmission housing when the input snapped.

Your signature line says 600 ft/lbs...don't cheap out on the driveline.

Carnage pictures and a nice diff yoke.

The reason GM uses the aluminum shafts on the trucks is because of the length.

A steel shaft can't be balanced properly at that length and tolerate the speeds they turn, they turn into a rope and wobble, which is why the older trucks and cars had carrier bearings in the middle. You just can't make a steel shaft that long in one piece. So when GM decided to get rid of the carrier bearing, they went aluminum shafts because they are lighter and don't get that whipping affect at high speed.

My wife broke the aluminum shaft in our Duramax a couple years ago, lol. I bought a brand new one from Spicer, the manufacture for GM, and comes complete with the 1350 sealed joints and a yoke, it was $750 through the driveshaft shop I use, and I got it at his cost.

One could technically take one of these and shorten it with your yoke installed, if it's a new shaft. I say that because some shops won't touch used aluminum shafts, for welding reasons. Dirty aluminum is a problem I guess and can be a liability. I know the local shop I use won't do used aluminum shafts. Only new tubes are used. I know one thing he complains about on the aluminum shafts, because he sees it all the time, they will not tolerate any road debri hitting them. All it takes is a little ding and they fold like a pretzel. So you absolutely can't have one accidently rubbing anything under a car, like a driveshaft loop for instance, and because they have to be such a large diameter, that becomes an issue.

I have our local shop build all the shafts for me, and although he does build aluminum, I have been using steel. Did one for dad's car last year with 1350 joints, billet yoke, 3" diameter that is very thick wall and seamless tubing. Cost was just under $600 and he guarantees it to 1000hp.

I had him build another steel shaft for me out of same material just slightly smaller diameter with 1330 joints for a stick car of mine and it was only $350 and guaranteed for 600 hp.

I'll be using him again shortly to build another 1000hp steel shaft for me with 1350 joints for the chevelle when I install the new 4L80E

There's always Carbon Fiber

Driveshafts have a "critical speed" which is based on length and other factors.

Years ago, when I worked for Truck Operations, the Ford Van guys were going crazy with Failures on the Driveshafts on the 10 passenger extended vans used in airport service applications.

After months of research the issue was finally resolved with a maximum speed red line for the vans.

The issues were caused by Airport Drivers of these vans delaying their departure times from the "Pick-Up" point of the trip and then subjecting passengers to travel times that would cause the passengers to miss their flights. Example leaving Lansing Michigan for the Detroit Metro Airport DTW on west side of the Detroit Metropolitian Area. About a 100 mile trip.

The driver would tell the passengers: "If you pay my ticket, I will see if I can get you to the airport for your flight. This required speeds of 95 plus MPH for the entire trip and possibly higher. The drivers would keep the money even though the van was never stopped by the police. Several Hundred dollars in some cases.

And so occasionally a high speed driveshaft failure occurred due to exceeding the "Allowable Shaft Speed" the shaft was designed for.

So if you decide to install that junkyard driveshaft in your vehicle or modify a driveshaft from a different vehicle, be aware you know nothing about designing a proper driveshaft for the speeds you will take the vehicle too.

It might run forever as a grocery getter type low speed vehicle, but rarely do Pontiac enthusiasts never go over 75 mph, or much higher.

Food for thought. BE SAFE OUT THERE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!

Tom V.

Again, to reiterate, my Firebird has a custom DS. This isn’t for that. Not really for anything. I was just thinking and decided to start a conversation.

Here is my rationale and how it got started. I have a 1952 gasser project. I installed a Chrysler 8.75 in it. Looks like it has tons of room in the trans tunnel. So I could go pretty thick in diameter.

I mentioned I saw a couple pop up while searching for hit rod parts. Then I noticed that 2500 HD trucks have like 5” aluminum shafts. As mentioned they are long as hell. So plenty of room to cut one down. (Or steel. I haven’t exactly performed thorough investigation of available parts)

I also thought to myself, “I have heard of more shaft failures on 4x4s rock crawling and stuff than anywhere else. Probably towing too”. So it would make sense that heavy duty trucks would have overkill driveshafts for a passenger car even in a performance application.

So the math to me said, you can get a heavy duty aluminum shaft, cut it down to a normal passenger car length and have 1350 ends put in it. If I ordered that shaft custom it would probably be the better part of $1000. Just made sense on paper at least.


I also recognize that anytime someone says “he can I cut this corner?” It’s going to raise suspicions. Completely fairly I might add. “Roadkilling” it has a habit of leading to breakage.

That said, there are plenty of success stories in repurposing factory parts for performance. 8.8 explorer rear ends, Lincoln mark 8 fans, etc etc. I think that if thought out, there could be something to this with proper parts selection and inspection.

Tom’s point is well made though as well. I am not a driveshaft engineer. Though I would generally assume the driveline professional at the shop would limit my stupidity when I brought the project to him.

My experience has been the labor modifying and rebalancing is significant and adding the new tube and yokes starts making a lot of sense, as always YMMV.

Used many Spicer aluminum shafts over the years with much success.

I hope I didn't come across as knocking your idea, because I wasn't. Thinking outside the box is interesting. In fact, what you are thinking might have a possibility of working. If you find a shaft like my Duramax, as I said it already has 1350 joints. You would simply just need a 1350 yoke to fit your application, and then find a driveline shop that is willing to do the work. The shop I use can remove the welded ends on any driveshaft no problem. He just turns the welds down in a lathe and the end comes out unscathed and read to reuse. The problem I run into is he does not like welding on used aluminum shafts. That would be the only hang up that I can think of.

You do not need to be a Driveshaft Engineer to be successful in your project.
You do need to find a quality Driveshaft Fabrication shop who can fabricate the parts for you and many of them will not warranty or even take on a job using used parts.

I wish you luck and hope you find a quality driveshaft fabrication shop who can build you a proper driveshaft.

I would try to talk with someone from Kaiser Aluminum in California about your project. They could point you in the right direction as far as quality fabrication shops.

Kaiser Aluminum
Manufacturer
Foothill Ranch, CA 92610

Tom V.

U-Pull-its have these aluminum driveshafts all over. I will continue to like steel, until the Slicks are no more.

My son runs an aluminum drive shaft in his mustang. It was factory equipment on the Cobra and they still offer it as a brand new piece from Ford Racing complete with yoke and joints, bolt in deal that is under $300. Not a bad price.

We've beaten the snot out of it at the track (and on the street) it's a stick shift, and it's holding up fine so far.

This. I also got the same driveshaft from Strange and I'll never have to be concerned about failure. You can look up a chart that shows the critical RPM for a given material, diameter and length to decide what you need.