Bent drive shaft. Anybody know the RPM's?

[HASSON1911]

Hello, the other day I took the crew cab out for a drive since she is mechanically sound, or so I thought. Seems the Main drive shaft is bent and causes violent shaking at . I'm having a new one made up but what is the RPM of this drive shaft at top speed, for when it gets balanced. For some reason I guess its cheaper? If they don't have to spin it up to what civiy trucks are running at. Anyways I have looked high and low, and even tried to use calculaters but 13,000rpms didn't sound right, but to no avail I'm begging for some help if you guys happen to know it. -Thanks, Jake

 

[jdknech]

if my math is right, it should not be over 3,500 RPM... the engine turns at 2,600 rpm max, and in 4th gear the trans is 1-1, so that would be your shaft RPM as well... 5th gear is overdrive (cant remember what the ratio is) but at .75 (i know its not this high) it would bring your shaft RPM to 3,850.. then again, i could be way off.. im just doing this in my head.. lol

 

[o1951]

Anyways I have looked high and low, and even tried to use calculaters but 13,000rpms didn't sound right, . -Thanks, Jake

Calculating is tricky - remember, for each gear under 4th, engine turns progressively faster than driveshaft. As JDK posted, only time drive shaft turns faster than engine is in OD gears. His calc is in the ballpark.

Solid, slow heavy diesel, not a civy gas engined car that can turn 5 or 6,000 RPM.

 

[gringeltaube]

if my math is right, it should not be over 3,500 RPM... the engine turns at 2,600 rpm max, and in 4th gear the trans is 1-1, so that would be your shaft RPM as well... 5th gear is overdrive (cant remember what the ratio is) but at .75 (i know its not this high) it would bring your shaft RPM to 3,850.. then again, i could be way off.. im just doing this in my head.. lol

It's whatever max engine rpm you see, divided by .79 (for the stock Spicer 3053):
2500 => 3165
2600 => 3291
2700 => 3418
etc.

So "not over 3500 rpm" is correct.

G.

 

[Moto4Life]

If you're running 9.00s, at 55mph the driveshaft will be turning at 3184-85 rpm

 

[tie6044]

Are you running a one piece shaft that you lengthened from a stock one or are you running a hanger bearing. I'm guessing your wheelbase is longer so I was just curious. It should be able to handle any RPM's your deuce can throw at it. We run deuce driveshafts in our mud truck and our motors spin at over 7000 RPM.

 

[Shawn MacAnanny]

I've had a couple made at Dennys driveshaft they are awesome and indestructible pretty much. Didnt have them made for the Deuce but for cars, but i dont see why they couldnt make one for you if you got the right measurements. Mi nitrous read steel driveshaft with lifetime warranty was only about $400 shipped u joints slip yoke and painted

 

[m-35tom]

if they ask you that question, you are at the wrong driveshaft shop. balanced is balanced. sounds like they are just guessing at it.

 

[G-Force]

if they ask you that question, you are at the wrong driveshaft shop. balanced is balanced. sounds like they are just guessing at it.

The reason they want to know what rpm it will be running at is so they don't manufacture it and balance it at a speed it won't be running at. And the speed it does run at happens to be the resonant speed (frequency) of the part they made. A resonant speed or frequency is the freqeuncy that a part naturally vibrates at. All parts have a resonant frequency. To find it you connect a vibration analyzer to it and strike it with a hammer. This is the frequency you do not want to be running at. If you do, the part will be in a constant vibrating state and will eventually fail or cause something else it is connected to fail. Another name for resonant frequency is critical frequency or speed. Trust me, I've had machines run at critical frequencies and it is real PITA and the vibration just gets worse over time. The cure is to either add mass to shift the frequency lower or higher or changing something else in the installation (mounting hardness or softness) to shift the critical up or down in the frequency range.
You never want to balance at a parts resonant frequency.