We suspect we have discovered why Ford does not paint the drive shafts in the super dutys!<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
<o></o>
So my buddy (a mechanical engineer student) is constantly complaining about his machine design project. I decide to actually listen to him for a change, and in his machine there is a drive shaft hooked to a gear or something... <o></o>
<o></o>
Anyhow we discussed this, and we believe the reason is: (he is typing now):<o></o>
<o></o>
The torque created from the trans to the axle could in theory create a torsional stress that would twist the axle causing the paint to flake off... sort of like the torsion bars on the chevy's that are plastic coated. Even if this does not permanently deform the drive shaft, but under full torque it potentially could twist. Also if the rear end is not perfectly centered and the suspension flexes it could try and bow the drive shaft also creating enough stress to pop the paint off. Even if your drive shaft never looks bent both of these theories could be possible because there is no permanent deformation until you get to the Yield Strength of the steel on the stress strain curve; for steel its about 30,000 psi.<o></o>

[start rant]So the long and short of it... if Ford didn't engineer the drive shaft with a large enough Safety Factor, allowing the drive shaft to twist any more than like .5 to 2 degrees they are hiding their lack of engineering abilities and not painting the drive shaft because they are already in production and don't want to waste money fixing the problem and paying an enineer that is sitting in his cubical doing noting right now to fix it.[end rant]

 

Very possible theory. The driveshafts probably do flex a bit just like the propeller shafts on naval aircraft carriers (they can look like a candy cane).

 

GM's are not painted either. In theroy you have a good point, HOWEVER in my findings I have never seen one "twist" unless its broken. Using some chalk or grease pencil and a timing lite you can easily check it.

 

I think it is because they save a few pennies per vehicle.

 

I suppose they could put 1000 lb driveshafts in so you could paint them but do you really want to carry around that extra weight? The give in the driveshaft probably goes a long way to making u-joints, gears, and tires last longer as well.

 

It's not a lack of engineering. Driveshafts do flex, it's not much but there are harmonics to it. Painting might dampen most of the vibration, but it would rattle off. Plus painting will add weight, which is unnecessary. Look at the Fuel tank of the shuttle, NASA quit painting after they found out how much weight it saved them. Adding weight to a rotating mass makes it harder too spin. Plus you would have to balance it after painting. It's a lot of work that is only going to make the shaft look pretty but will not enhance it's performance.

If you want a solution to the pretty and functional, get an aluminum or carbon Fiber shaft made. We used to use Racing Drive Shaft Distributor, Custom Driveshafts, Carbon, Aluminum Hot Rod Driveshaft Supplier The metal matrix composite is 40% stronger than the Aluminum alloys, shiny and weigh about half of a stock driveshaft. We were replacing 54.25" 33lb with the MMX weighing in at 16.5lbs. They have DOM as well and balance them to 7000rpm, about 2k rpm faster than a stock/average shaft.

 

yup its entierly possible to destroy ujoints if u put to much of anything (be it paint or undercoating) onto a driveshaft...

just being a small amount of out of phase wil quickly make a lot of vibration at speed for your poor driveshafts ujoints to deal with...

anytime i've had a vehicle undercoated i've made good and sure the driveshaft doesnt get done..

 

I don't believe driveshafts flex much at all. I don't think they're designed to, and I don't think they need to. In fact, hypothetically, if a driveshaft flexed too much (rotationally), it could cause vibration by making the u-joints out of phase, but realistically that would require quite a bit of rotational flex.

Axles, on the other hand, as I understand it, are designed to flex rotationally. I have heard and read that the ends, where the splines are, are induction hardened, while the rest of the shaft is not. So they will twist under load, which is a good thing if you are trying to eliminate driveline shock, without causing any u-joint phasing issues.

And consider this. The axles have four times the torque on them that the driveshaft does, so you can have a fairly stiff axle and still get some flex. And with this in mind, why would you want to have a driveshaft that flexes? You wouldn't need it, since the axles would absorb the driveline shock.

Finally, look at how driveshafts are constructed. Hollow drum-shape, fairly light material, placed out at a fairly large diameter. Taking advantage of the lower force at the larger radius (for a given torque), allowing lighter material. I think if engineers wanted to make a driveshaft that flexed, they wouldn't make it hollow, they would make it solid and a much smaller diameter. If you rotationally flex a hollow tube, it is very difficult to control how and where it flexes. Twist the ends of a paper towel tube and it will start to collapse somewhere, since there's no material in the center to prevent that.

 

I think there is a bit vocabulary that needs cleaning up. Flex is being used to describe deflection and distortion. A driveshaft will sing at a high enough speed, most are only balanced for 4-5k rpms, which at those speeds it is relatively true. However because above those speeds it will begin to distort and create an audible vibration. This tiny little vibration still occurs at lower speeds, but isn't noticable (either by sound or simple measurements.) However this vibration is in place. It would work like an ultrasonic cleaner and bust the paint loose if it wasn't perfectly bonded.

 

Heck, remember the early 60's Pontiac Tempest? I had a rubber driveshaft with a curve in it !

 

I've painted mine with black chassis on my last two trucks. Towed and worked them plenty. Never had any problems of any kind including never had the paint flake off. Even if a shaft did flex, Ford could certainly paint it was paint that flexed too. Look at plastic bumpers. Can flex all the time and never flake off. Bottom line is Ford doesn't paint driveshafts because they don't need to. They will never rust through so the protection aspect isn't needed. It's under the vehicle, so appearance isn't key. Well, unless your guys like us so I say paint um up. My new one will be as my past ones have.

 

I think the most stress we actually have to worry about on our driveshafts is the moment (and by moment I do not mean a period of time, I mean the static load moment) at which you just apply the throttle and the rear end is on a good traction surface. The drive shift will 'flex' because each action has an equal but opposite reaction. The moment may not exceed the elastic region of the material used, thus we wont have any permanent deformation but it definitly deforms. Then we have Hooke's law to explain how all that is going to play out.

Either way, it does make sense to save money and not paint the drive shaft especially if the paint may not bond and a powder coat process is slightly pricey.

 

your not kidding!!!! looks just like a candy cane

YouTube - Maine Maritime Academy - Propeller Shaft

 

Funny effer ain't ya. On a real ship (think USS Ronald Reagan) the drive shafts will twist about a full rotation due to the amount of torque they generate (250000 ftlbs or so) per drive shaft. Of course their shafts are designed to flex like that.

 

khjvgkjkjgjhg