driveshaft- one pc vs twp pc
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Fleet Mechanic
Joined: Jan 2010
Posts: 1,287
Likes: 77
From: spring hill fl
driveshaft- one pc vs twp pc
so i'm going to be swapping a 302 / 4r70w in place of my 360 / c6. first truck I've had with a two piece. since i'll need a different length shaft for the swap, is there any reason not to swap to a one piece shaft?
Believe Nothing
Joined: Jun 2004
Posts: 7,514
Likes: 398
From: W. Central FL.
A given length driveshaft can only run at a certain speed without setting up damaging vibrations. This is one reason why some vehicles run two piece driveshafts. There are several sites that discuss this. I believe this site will cover the basics.
Driveshaft Safe Operating RPM Calculator | Spicer Parts
Another: http://www.dennysdriveshaft.com/pote...alculator.html
And yet another: http://www.hotrod.com/articles/ccrp-...alancing-tips/
Driveshaft Safe Operating RPM Calculator | Spicer Parts
Another: http://www.dennysdriveshaft.com/pote...alculator.html
And yet another: http://www.hotrod.com/articles/ccrp-...alancing-tips/
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
The longer the driveshaft the larger OD n thicker wall thickness it has to be to eliminate deflection or "whipping".
it can also result in loss of ground clearance.
it can also result in loss of ground clearance.
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Lead Driver
Joined: Apr 2011
Posts: 6,399
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From: El Dorado, Arkansas
The bending (whipping) of the driveshaft is known as the critical speed rating of the shaft. Everything has a natural frequency. If the shaft reaches its own resonant frequency, it will self-destruct.
Driveshaft Critical Speed
Driveshaft Critical Speed
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Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
The bending (whipping) of the driveshaft is known as the critical speed rating of the shaft. Everything has a natural frequency. If the shaft reaches its own resonant frequency, it will self-destruct.
Driveshaft Critical Speed
Driveshaft Critical Speed
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
Critical speed of the shaft is more of a concern with an overdrive, when in overdrive, since the driveshaft will be spinning faster than the engine and faster than what it would be turning if a (non-overdriven) transmission was simply 1:1 in high gear.
Hotshot
Joined: Mar 2013
Posts: 14,255
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From: Phoenix, Az.
Ford nor aftermarket listed a separate carrier bearing. So I had it sent out to a driveshaft repair company. They gave me the choice of them machining to make one fit or a one piece shaft. They pushed more for the one piece. I said no. Fix the two piece. I figured there had to be a reason why Ford went 2 piece. And now I know why!
Thanks guys.
Senior User
Joined: Jul 2010
Posts: 239
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If you're driving at the same road speed, say 60 mph, your driveshaft won't be spinning any faster with overdrive. If you have, let's say a 3.54:1 diff gear, your driveshaft will turn at the speed of the diff ratio (3.54 turns for every one). The engine rpm is what would change, with overdrive the engine would run slower.
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
If the output shaft of the transmission (and thus the driveshaft) was turning slower, then this would be known as an underdrive.
See explanation of what makes an under/overdrive.
Overdrive: What Does This Mean? | Gowesty
See explanation of what makes an under/overdrive.
Overdrive: What Does This Mean? | Gowesty
Senior User
Joined: Jul 2010
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Well, I'm not sure if we're on the same page, but I'm assuming that the comparison is being made at the same road speed with the same diameter tires and the same differential gear ratio. If the road speed is the same and the tire size hasn't changed and the gear ratio of the diff hasn't been changed, then the driveshaft speed cannot change. It doesn't matter whether the transmission has overdrive or not. The only thing that would be different would be the engine rpm.
Now, if we are not doing the comparison at the same road speed then all bets are off. For example, if the engine were driven in high gear at the same engine speed, lets say 2500 rpm, and the tire size and final drive ratios were equal in both trucks, then the truck with overdrive would have a driveshaft spinning faster than the truck without overdrive. The truck with overdrive would also be traveling at a higher speed.
Now, if we are not doing the comparison at the same road speed then all bets are off. For example, if the engine were driven in high gear at the same engine speed, lets say 2500 rpm, and the tire size and final drive ratios were equal in both trucks, then the truck with overdrive would have a driveshaft spinning faster than the truck without overdrive. The truck with overdrive would also be traveling at a higher speed.
Senior User
Joined: Feb 2015
Posts: 294
Likes: 1
FEcruzr69 is correct. Driveshaft speed is determined by rear gear ratio, tire diameter, and road speed. Unaffected by transmission. It could not even have a transmission, and the rearend pinion would turn the same speed at the same road speed,.