one piece driveshaft advice
- Thread starter dragracer
- Start date
Neither of which can do 150 mph stock.
Anyone remember this (pictures seem to be AWOL, too bad they were impressive):
http://www.supramania.com/forums/sh...but-would-you-expect-less&p=719571#post719571
Anyone remember this (pictures seem to be AWOL, too bad they were impressive):
http://www.supramania.com/forums/sh...but-would-you-expect-less&p=719571#post719571
rhs;2043012 said:
That's actually a great example to prove my point. Ford used a special metal matrix aluminum (not regular old 6061 aluminum) on their one piece shafts. To my knowledge, no aftermarket driveshaft company makes MMC Aluminum driveshafts. They're traditionally 6061.
On the P71 when Ford fitted a regular aluminum DS they lowered the speed limiters to 120 mph because Ford engineers determined the one piece regular aluminum was unsafe beyond that speed.
Ford was so worried about driveshaft failure that they limited the speed of the car solely to prevent failures from the one piece aluminum driveshaft.
Crown Vic Info site/Wikipedia said:
Since the OP was looking for steel this isn't really an issue for him, but given the potential safety concerns I think it's a valid point worth beating to death...
Yeah, I have a buddy who had a 3" aluminum shaft explode underneath him from spinning it too fast.
Knowing the critical speed is verrrry important to avoid that. I wish there were some aftermarket 2-piece shafts...
Knowing the critical speed is verrrry important to avoid that. I wish there were some aftermarket 2-piece shafts...
suprarx7nut;2043035 said:
I know they were metal matrix, but the speedometers didn't go up to 150. My 1995 stopped at 140. I was told by a cop friend that they were limited due to tires.
I don't want to say the plain aluminum driveshafts didn't have concern, but some of that info doesn't add up.
3p141592654;2043019 said:
I can post videos from youtube showing turbos exploding and rims falling off, that doesn't mean they should be avoided like the plague. That's the result of either a defect or of an impact causing damage to the shaft...no excess speed, excess power or excess rpm. Scare tactics shouldn't be the primary driving power for a purchase.
suprarx7nut;2043035 said:
Yes, a one piece driveshaft can be devastating when it breaks. So can a wheel bearing, or a broken tie rod, etc etc. The question you should be asking is: can it be made safely and engineered to a point that it will not break under heavy use? The answer is yes, and that is why they are being manufactured and sold.
rhs;2043044 said:
What I'm reading says the police versions generally had the Metal Matrix Composite shaft and had a limiter set to 140-150mph. The civilian versions came with a regular aluminum and were limited to 120mph. Ford may have also fitted lower grade tires, but the speed limitation was based around the driveshaft and only the driveshaft from everything I've read.
SideWinderGX;2043048 said:
The engineering put into the aftermarket driveshafts is a small drop in the ocean that is OEM engineering at a company like Toyota. Toyota (and others) will spend more labor investigating this stuff than the aftermarket driveshaft shops will in centuries. It's not like those driveshaft shops with a lathe and a balancing machine all have a PhD'd principal engineer signing off on their designs. They're machinists throwing their work on a balancing machine, making sure it will balance in the shop and shipping it out. They may have an engineer or two to help out, but that's it. Meanwhile OEMs hire teams of engineers with Masters/PhDs to verify work and invest millions $$ into stuff like this looking at exactly how safe it is in the long term in all driving conditions.
The organizations that are putting serious efforts into this topic seem to all be coming to the same answer: they'll pay more money to install a heavier product because they have concerns over long term reliability on the cheaper, lighter one piece designs.
If you're going to run a one piece driveshaft take a good look at a carbon shaft. That is really the best of every world. Lightest, Safest and often Strongest (except for chromoly, i guess). It may be a little more expensive, but the benefits are huge. A carbon driveshaft is never going to tear open your floorboard or cut fuel/brake lines. One piece aluminum/steel have done exactly that.
I'll stop beating this drum I guess, but the info is all out there if you hunt for it. Safety, Vibration, Durability. Manufacturers spend more $$ to avoid those 3 potential problem areas one 1 piece shafts. You can find interviews of engineers working for OEMs explaining why they spend more money to use a heavier, lower "performance" shaft. If they do 1 piece, they use carbon because it's quiet and safe. Still not durable, but at least it won't lead to an accident as easily.
SideWinderGX;2043048 said:
If you read the whole thread you'll find that the critical speed of that driveshaft was 80mph. So it was not a defect or impact, but bad design and ignorance of its limitation. At the very least, everyone with an aftermarket DS should know their new critical speed e.g. http://www.wallaceracing.com/driveshaftspeed.htm
I hardly think that applying some common sense engineering is a scare tactic. Be informed, make good decisions.
suprarx7nut;2043054 said:
Your concern is appreciated but your argument solely revolved around the fact that you believe that OEM manufacturers have it right because they have more money and are probably smarter than us. Go look up what an 'argument from authority' is and try to understand why what you're saying doesn't really have any merit.
Critical speed of a shaft is one equation, which we have all the variables for. There is no 'magic OEM sauce' which makes car manufacturers better apt to punch the numbers into their calculators. No offense, but your post is riddled with 'in my opinion' and 'maybe' and 'tons of money'. I'll pull this card, since your riding the OEM horse pretty hard: do you have an engineering degree? Have you designed anything before? Do you understand how things are designed and what criteria are used in order to come up with a finished product?
It's hard to even respond to your post because it doesn't contain any facts, it just restates your opinion that 'OEM is the only way' again and again.
3p141592654;2043060 said:
If you read into my post you'd realize I was making a statement regarding inferior products. We're on the same page.
edit, because I don't want to make a third post in a row: my driveshaft is right around 42" long (why is everyone quoting wheelbase length in this thread? That has nothing to do with driveshaft length...). Shaftmasters sent me a 3", .125 6061 shaft which, using that link 3p, comes to 12,286 rpm as the critical speed. Assuming I could get my auto to have 0% slip in 4th gear without burning the TC up, that would mean the engine is churning at 8600 rpm exactly.
First off, critical speed is not some magical number which will make something explode immediately. It is a resonant frequency which something will vibrate at, IF it is out of balance or it starts to resonate.
Secondly, I think the OP of that other post (with the broken driveshaft) meant to say his half critical speed is 80 mph, not his critical speed. You'd have to go out of your way to make a driveshaft so weak, or so small, that its critical speed would be 80 mph.
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SideWinderGX;2043062 said:
Yes I am a degree'd engineer. BS in Mechanical Engineering, University of Colorado. I make a living designing things and managing projects that design things. Literally. I design equipment and sign off on official engineering drawings of my designs, design updates from others and temporary deviations from previously designed and certified equipment. I don't work in the automotive industry, but I am an engineer with experience designing moving parts and static load bearing parts. So for what that's worth... there ya go.
I'm sorry my post has a lack of facts. The numerical information regarding this topic is generally proprietary info so I don't have access to anything more than interviews of engineers and other public comments. I understand just because they spend more, doesn't mean they understand it better. However, there is something to be said for a large collection of companies, employing a large number of more educated and experienced engineers, very concerned with cutting costs where ever possible and all choosing to spend extra money for worse performance. Safety/durability is king to these companies. I certainly don't know enough to doubt all the OEMs. Do you feel as though the various aftermarket driveshaft companies know more than the collective global OEM automotive industry? That's not where I'd put my money...
Here's a formula that makes the 1 piece designs less appealing. I won't fill in numbers, but like you said, anyone can do that.
Rotational Inertia = Mass x Radius ^2
This shows that the radius has an impact to the second degree. This means changes in diameter affect performance more quickly than a proportionate weight savings. The aluminum shafts are lighter, but of larger diameter (generally 3-4" for our cars). This means their advantage is less than the commonly claimed "weight" figure. If you really want the performance increase you need to plug in the weight and the radius of that weight (approx radius of the shaft). The inertia difference will be less than the weight savings when using a thicker shaft (which the 1 piece always are from what I've seen). As I recall the OEM shaft was around 2.5-2.7 inches diameter so assuming the same weight a 3" diameter shaft would have ~20-35% more inertia. Take that rough figure and subtract that percent from the decrease in weight and you have your overall performance increase.
Critical mass calculations are helpful to see the theoretical limit of the material. It's not so helpful for real world situations where the shaft could get knicked by road debris, ice build up, have caked on dirt/oil or any other external factor. The one piece designs have a longer length (obviously). The longer length means it takes less additional mass to unbalance the shaft and lead to vibrations or catastrophic failure. I dont have a formula handy, but my guess is that the length is proportional (to the first power) of the shaft's reaction to unbalanced weight. This same principle holds true for dents, dings and to a lesser degree, scratches.
As Pi said above, it's just important for people to understand some of this stuff before they modify a potential safety item in their car. Unlike removing you airbag, which will just impact you, a driveshaft failure on the highway could easily impact fellow road goers. I don't mean to be overly "OEM only" or to argue with you. Hopefully you've read the discussion in a friendly demeanor.
It would be great to look at failure rates and vibration measurements between the two options on a large scale. I'm not sure such info is available to the public. I'd bet my savings account that at least a few OEMs have that exact data from their own research while making million dollar driveshaft decisions on new performance cars.
The calculator I reference above is an idealized solution, and ignores some real world details. It gets you close, but a real manufacturer is going to use a 3D FEM solver from Ansys or similar and actually solve the problem properly. That takes money, expertise, and expensive tools which the mom & pop shops rarely can afford. Then they'll back up the modeling with some real testing. It all costs a lot.
Of course you want to run at some backoff from CS. How much is always an engineering compromise. In addition, you need to factor in manufacturing tolerances, and that over time the shaft will become subject to wear, damage and other intangibles that eat into your margin. I am pretty sure none of this was ever analyzed by the aftermarket driveshaft people for our specific application.
Of course you want to run at some backoff from CS. How much is always an engineering compromise. In addition, you need to factor in manufacturing tolerances, and that over time the shaft will become subject to wear, damage and other intangibles that eat into your margin. I am pretty sure none of this was ever analyzed by the aftermarket driveshaft people for our specific application.
suprarx7nut;2043067 said:
BS in Mechanical Engineering Technology here, from RIT. Why can't you look at this situation objectively and calculate the critical speed of the driveshaft yourself? If you want to put all your chips into the 'OEM' bag just because you think their solution is the best under all scenarios be my guest, but don't tout it as such because it isn't backed up by anything except your opinion.
My educated guess? You don't have to worry about critical speeds when you have a two piece driveshaft, each piece only being 20" long. A 2" diameter tube, .125 thickness, 20" long has a critical speed of 35,000 rpm. You could bend it into a Z and it still wouldn't wobble. Easy for the OEM, no balancing needed. Carrier bearings? Cheap when you're ordering them by the 100,000.
It is not the same weight, stop assuming things like this. The stock driveshaft weighs 30 lbs, the aluminum one piece from shaftmasters weighs 11. Let's assume the stocker has a 2" diameter (its bigger than this from memory, so I'm giving this example some leeway). If we compare this to the shaftmasters with a 3" diameter the shaftmasters has 17.5% less inertia. Still better, and it weighs less.
Yes, no offense intended
Just frustrating haha. If something becomes unbalanced you would know immediately, just like a bent rim. If someone continue to drive the car hard at 150 mph after you KNOW something is damaged, there's not much anyone can do to help that person. On the same note, if you're on the highway and run over something heavy enough to kick up and damage your driveshaft, your DS isn't going to be the only thing damaged underneath your car from that object. I hope you're pulling over after that.
3p141592654;2043068 said:
Agreed! The 'bigger hammer' solution to this is to move up to a 3.5" driveshaft (14400 rpm critical speed in my 42" application).
Wear and tear eats into all parts of a vehicle, and like you said it will affect a larger diameter driveshaft more than a smaller one. I'd be puzzled if someone ever said they needed to get their DS rebalanced after 20k miles...what are they driving over?
SideWinderGX;2043070 said:
Neither you or I have the computational horsepower to calculate this objectively and completely though. Critical speed is theoretical and ideal. It's a good starting point, like most theoretical physics involved in engineering. It's not all there is to consider. It's like the constant joke in engineering school wear your problems are calculated in an imaginary world where friction doesn't exist and everything is "ideal". When designing parts exposed to the atmosphere and road debris, like a driveshaft, you have to be a little more broad in your analysis until you can either spend $$ on thorough FEA (the mom and pop shops likely are not doing this) or doing a large number of real world tests (the mom and pop shops are also likely not doing this in a meaningful quantity in real world conditions).
I would like to be perfectly objective here, but I can't. The closest we can come is looking at the formulas we do know and how other folks with the resources to thoroughly test it out have chosen to go. I think the decisions of OEMs across the globe is very meaningful. If a one piece aluminum shaft could be made safely, with performance gains, one of the OEMs would have figured that out by now and the engineer responsible for the change probably would have been given a massive, massive bonus. They only time an OEM uses a one piece shaft for production applications is when they use it on a POS car that can't go fast (120 mph speed limiter above) or when they use a special compound stronger than regular 6061 aluminum.
I too prefer objective measures, but expert judgement is also an engineering tool and technique.
SideWinderGX;2043070 said:
I know it's not the same weight. My point is that the difference in inertia is what matters. It's easy to get everyone excited about one piece aluminum driveshafts when the weight is 70% less than OEM. The difference in performance (inertia) when accounting for the increased radius is around half that percentage. So the performance increase is half what most folks will think. That's significant when weighing your options. That's all I'm saying.
SideWinderGX;2043070 said:Yes, no offense intended
If something becomes unbalanced you would know immediately, just like a bent rim. If someone continue to drive the car hard at 150 mph after you KNOW something is damaged, there's not much anyone can do to help that person. On the same note, if you're on the highway and run over something heavy enough to kick up and damage your driveshaft, your DS isn't going to be the only thing damaged underneath your car from that object. I hope you're pulling over after that.
Agreed you should stop if you're going 150 and hit something. But this stuff is dangerous at 65mph. Did you ever catch the article/post from the guy with a modified (corona/corolla maybe?). His was an extreme example, but I don't recall him going insanely fast. He had a failure in the driveshaft and it sheared either his brake lines or air ride lines or just air ride lines. He had air ride suspension so everything was worse than normal, but he was basically a metal sled once it happened. No brakes, no suspension, spilling fuel, grinding down the road.
These failure aren't normally a long standing vibration that's just ignored. They seem to be either no warning or a very subtle vibration until catastrophic failure. Youtube driveshaft failure. Lots of neat, rather sudden explosions. I don't believe any of these are anywhere near the theoretical critical speed. Funny how most the driveshaft failures seem to be on Mustangs, haha.
https://www.youtube.com/watch?v=qXzuEIwd9-M
https://www.youtube.com/watch?v=bXU1O2Dhxpk
https://www.youtube.com/watch?v=nAm59oe0RPU
suprarx7nut;2043078 said:
First, come on, go look up 'argument from authority'. It's getting annoying. That shit belongs in a church, not in an engineering discussion.
Very little pieces of the car are actually tested in any type of FEA analysis software. Most of the parts are modeled for fitment, and most are physically made and tested, but FEA is reserved for very few parts of the engine/suspension itself (unless you're Ferrari or Koenigsegg where you can justify the extra time and cost because the cars sell for so much).
You know as well as I do that the atmosphere and friction doesn't affect critical speed, its a relationship between material, diameter, length and wall thickness. That's it. Grouping this in with other complicated calculations is a slap in the face to the science behind the equations and those who have used it for decades. Just because a computer can do the work for you doesn't mean the equations are to be ignored, because they always coincide.
Have you measured a stock driveshaft? What is the diameter?
The V6 mustang diveshaft is a 2 piece steel driveshaft, right up your alley. Because Ford is filled with lazy union morons, they thought that not balancing the driveshaft at all would be a good idea and that's why its rated so low (and explodes). OEMs are not infallible from making mistakes, and OEMs do not use FEA analysis software for most of their designs.
Back to my original point: a well designed and balanced one piece driveshaft is superior to the stock 2 piece driveshaft, and staying away from properly constructed one-pieces is ignoring the hard scientific and engineering evidence that they were designed upon.
Ebay turbo exploding on a 2JZ: https://www.youtube.com/watch?v=w4sH4pLlSRo
2JZs aren't to be avoided, nor are turbochargers. Cheaply made (and cheaply priced) ebay turbos should be avoided...just like cheaply made driveshafts, and connecting rods, and wrist pins...the list goes on.
SideWinderGX;2043111 said:
Argument from authority. I get your point. Can you model a 49" driveshaft made from 6061 spinning at X RPM with XX grams of unbalanced mass while under a lateral force of X Gs and a twisting force of X? I can't. OEMs can. Do a quick search for "Ford FEA engineer". Even the "lazy morons" at Ford spend dedicate hundreds of engineering jobs to FEA. LinkedIn currently lists 15 jobs at Ford with FEA in the job description/qualifications fields. I can't believe you don't think they run FEA on every part under load. That's insane. Of course they do. I bet they do FEA on interior trim pieces. No joke.
Where do you work where they don't do FEA on parts under load or in motion? Any time I design a part that could in any way ever be a safety issue, we do our own FEA/load modeling. And that's for very small quantity parts. Of course big OEMs do that. I... I... don't know what else to say.
SideWinderGX;2043111 said:
Atmosphere doesn't matter? temperature doesn't matter? material build up doesn't matter? Sure, air friction doesn't really contribute much, but you can't approximate all the needed calculations ignoring real world stuff. Ice build up happens. Road debris can and does damage parts under the car.
Yes and I provided the approximate numbers above which i used to come up with the ~30% additional inertia factor. Sigh, I'm going in circles here.SideWinderGX;2043111 said:
SideWinderGX;2043111 said:
I know some of those are two piece shafts. My point is that they explode with instant force. They don't limp.... limp.... limp then give out. They're fine..... and then BOOM! That's what makes it such a critical safety issue.
OEMs are not infallible, but they absolutely do use FEA when designing most parts. Their job postings say they do. Their engineers talk about using it. I'm sorry... they just do. They also pour lots of engineering into vibration and cabin resonance.
In what way is a 1 piece superior? It is lighter and generally has less inertia. It also has fewer joints and that's a positive. Aside from that it's a liability due to its decreased tolerance for lateral movement of either end of the shaft, decreased mass required to make it unbalanced, decreased damage resistance before catastrophic failure, etc...
I know we're not seeing eye to eye here and that's fine. But OEMs definitely perform FEA analysis on this stuff, and most every component in the car. That's a large part of what they hire engineers for. I should know, I've been job hunting with OEMs for years...
suprarx7nut;2043115 said:
I strongly disagree. No amount of computer testing (excusing situations where its the only possibility) will ever be as good as real world testing. Not every part is FEA tested, every part IS however physically tested.
Unbalanced mass can be calculated easily. Any force, torsional or otherwise, will not affect the critical speed but will test the physical strength of the tube, ujoints and bearings of the differential.
"I bet" they do FEA on interior trim pieces. You're putting a lot of faith in the OEM companies without any proof :biglaugh:
Yes, they matter. No, they don't matter in this specific case. Everything has its place...and atmospheric and temperature conditions do not come into play in driveshaft design. If the miniscule amount of air whipping around your driveshaft unbalances it, you shouldn't be designing driveshafts. If the 20 or 30 degree swing in temperature during use upsets your driveshaft...same thing. Neither will upset or unbalance the driveshaft. Temperature would only affect the length of the shaft, and that's why slip joints exist.
Quick math:
Stock - 30 * 1.25 * 1.25 = 46.875
Alum - 11 * 1.5 * 1.5 = 24.75
Units are irrelevant as both equations use the same units, all we care about is the difference. You claim 30%...I'm seeing an almost 50% reduction in inertia going to the aluminum one piece, and that's using your best case measurement. If we use a radius of 1.375 (diameter of 2.75) we get 56.72, we get a 56% reduction in inertia. Much, much better.
I've spoken at length with many engineers, and some 'engineers', who work at production facilities for OEM companies. What you're claiming does not happen to every part. Critical pieces, and parts that break under physical testing? Yes. Every part no matter what? Absolutely not. No one has the budget to FEA test every single part.
A driveshaft is not a safety issue just because they can explode under the worst possible situation. So I shouldn't handle a rifle because it might backfire and explode? Or maybe I should 'treat never keep keep' because that's the safe way to do it...I can list a thousand different parts on any vehicle that could break and result in a fiery death, but this all leads back to proper calculations and construction in the first place. The 'scare tactics' you are using in your argument mean absolutely nothing in face of engineering.
Here's an example of how ridiculous your argument is: unbalanced and broken torque converters/flex plates have been known to take people's legs off and cause extreme damage to the interior of a vehicle. This does NOT mean that every single transmission needs to have a transmission blanket on it. TCs and flex plates have been used for many decades now in literally billions of cars, and the few that explode is not any reason to raise up pitchforks and decry the use of torque converters. Design them right, use proper procedures to manufacture and install them, and you'll be fine.
Wow, we certainly hijacked this thread.
I'm going to wind down our side argument with a couple more comments.
FEA is not always a long time sink. You can run basic load simulations in seconds with a modeled part in CAD software. If nobody is running even basic stress calculations (with ANSYS or just basic SolidWorks modeling) I'd be shocked. Maybe I'm wrong, I dont know.
Temperature swings? not just 20-30 degrees. About 5 to 6 times that, assuming you're talking F and not C. At those temperature swings materials (metals, especially) have changing strengths and elasticity that impact how they behave.
Production is very different than design and research. Different locations, different management, different functional purposes, different priorities. Design and research is what I'm talking about. Production engineers would definitely not care about this stuff.
Driveshaft is absolutely a part which is viewed from a safety perspective. It's about the likelihood of failure and the consequences of failure. That's weighed for all moving parts in engineering design decisions I've ever had any involvement in.
That's it. I'm tapping out, haha.
I'm going to wind down our side argument with a couple more comments.
FEA is not always a long time sink. You can run basic load simulations in seconds with a modeled part in CAD software. If nobody is running even basic stress calculations (with ANSYS or just basic SolidWorks modeling) I'd be shocked. Maybe I'm wrong, I dont know.
Temperature swings? not just 20-30 degrees. About 5 to 6 times that, assuming you're talking F and not C. At those temperature swings materials (metals, especially) have changing strengths and elasticity that impact how they behave.
Production is very different than design and research. Different locations, different management, different functional purposes, different priorities. Design and research is what I'm talking about. Production engineers would definitely not care about this stuff.
Driveshaft is absolutely a part which is viewed from a safety perspective. It's about the likelihood of failure and the consequences of failure. That's weighed for all moving parts in engineering design decisions I've ever had any involvement in.
That's it. I'm tapping out, haha.