Driveshaft reconfig questions...

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serrata

Well-known member
Joined
May 18, 2012
Messages
91
Location
Orlando, FL
Here's the issue. My donor is a long bed 4wd F350 dually crew cab. My rat will essentially have the same drivetrain layout, but the engine will be slid much further back, meaning I need a shorter rear driveshaft and a longer front driveshaft.

I'm not a mechanic, so just assume I'm dumb. :confused:

1- For the rear driveshaft:
The rear driveshaft has 2 segments: A longer one in the back attached to a shorter one with a yoke in front of that. The shorter one is braced t the frame.
The length of the shorter one is essentially the length I need.
It has a fixed brace on it that originally attached it to the F350 frame.
Can I take that brace off and use the shorter shaft with the yoke?


2- For the front driveshaft:
The idea is to push the front axle out in front of the engine instead of under it.
I would like to add a segment with a fixed frame brace on it, like the original rear was, so that I can have a shaft from the transfer case toward the front and braced to the front of the new frame in front of the engine with a joint attached to the existing front driveshaft.

What are my options for doing this?
 

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The way it's designed the drive shaft is fixed from the tranny to the carrier bearing, after that you have a slide to allow for travel of the rear end arc, as the rear moves up and down the shaft slides in and out. On a single drive shaft the yoke on the tranny does the sliding.
Here is how I did mine just for visual, I kept the front so I wouldn't have a big tunnel in the cab and then let the travel take place after the carrier.

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Staring at this for a minute, my original on the f350 was the same, just much longer.
I assume the shaft goes the majority of the way into the yoke, so that the centripetal force doesn't fling the u joint out.
 
How does this work, sneaky? [S Looks to me, like the shaft would leave the scene immediately...

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.

I agree, U joint looks to be too far back from the slip yoke. On semi's, we have a short driveshaft from the rear of the front diff to the front of the rear diff, the shaft is about 3-4" long from the front joint, then there is the slip joint, then the rear section of driveshaft is 2' or longer depending on the axle spacing.

As to the original poster, You are going to have to change the yoke on the transmission if you can, if not, you may have to use the front part of the front driveshaft welded to the rear of the rear driveshaft, that way you can have a joint at both ends. Might have to build a custom shaft using the original ends.
 
Are those mock up pics that show the sitting heights of your axles and trans? Will you be using bags? If so, keep in mind that the distance between axle and trans will get shorter when you inflate. Usually tail shaft space is about 3/4" from the housing, but with a frame dragger, that has to be measured when fully inflated. (Yeah, the one thing I nearly screwed up when I did my air ride)

Pay attention to what your U-joint angles will be at ride height. Too tight an angle could cause grief.
 
How does this work, sneaky? [S Looks to me, like the shaft would leave the scene immediately...

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It works perfect, the slide allows for all the movement of the rear on bags, and at ride height the shaft is in line so no harsh angle. The front has a long spline that the slide slips up on so I don't see where you think it can jump out of alignment?

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I cut nearly 3ft off the rear section of drive shaft.

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Or get a sliding yoke for the transfer case from a single shaft and use a short one piece shaft.
 
Excellent. Thanks guys.
Is the yoke supposed to slide freely, or is it supposed to be very tight?
Mine is currently very tight. It required a hammer to knock it back on.

Here's what I did today:
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I basically just moved parts around. I took off the u joint from the yoke on the big driveshaft and connected it (temporarily. Need a new ujoint cap) to the rear diff. The shorter driveshaft got the carrier bearing bracket removed.

So, I have a u joint on each end and a yoke in the middle. I will be using airbags, so it does look like it will compress the shaft into the yoke as it rises to drive height.

Does this look ok??

Also, I plan on keep 4wd. The front driveshaft is now going to need to be extended and have a carrier bearing and midpoint pivot. I plan on having a frame cross-member where the board is. It looks like the longer rear driveshaft is about the right length to cover the gap. Can I use it for this purpose? It looks like the u joints for the front and rear shafts differ quite a bit in size. I guess it doesn't matter since whatever I put in that place needs to have a carrier bearing. Are front driveshaft carrier bearings a thing, or do I need to adapt something?
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The front has a long spline that the slide slips up on so I don't see where you think it can jump out of alignment?

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It looked to me, like the universal joint would (naturally) "run out" and chew the splines to hell.

Your short shaft :rolleyes: is deceiving, but if you have LOTS of spline engaged, I'll shut my trap and move along. ;)

.
 

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Excellent. Thanks guys.
Is the yoke supposed to slide freely, or is it supposed to be very tight?
Mine is currently very tight. It required a hammer to knock it back on.

The rear slip joint should move freely and your u-joints are out of phase. Pull it apart, rotate and get the yokes in line with each other... they should be aligned like your front shaft.

A carrier bearing will not work for the front, unless you add another u-joint. Lengthen the shaft.


Edit: What in the world are you doing here? Rear shaft in the front, front shaft in the rear????


.
 
Just saw your other question from your edit.
The rear originally had 2 shafts, one before the carrier bearing and one after. I'm just eliminating the one after since the overall length is now much shorter in the rear. (the engine is farther back now)

For the front driveshaft, I'm not sure yet. Because I'm extending the front axle way out in front of the engine, I need more length to the front driveshaft. The distance is so long now that it looks like I'll require a carrier bearing.
 
The rear slip joint should move freely and your u-joints are out of phase. Pull it apart, rotate and get the yokes in line with each other... they should be aligned like your front shaft.

A carrier bearing will not work for the front, unless you add another u-joint. Lengthen the shaft.


Edit: What in the world are you doing here? Rear shaft in the front, front shaft in the rear????


.
Trust the good doctor. He knows of what he speaks. Even if you get all the pieces to "work" together, you will likely have to have the final assembly balanced by a professional driveshaft shop. These critters are really not made to mix and match like this. Phasing can still be wrong, even when it looks right. This will cause vibration that will lead to driveshaft failure, which is not a pretty thing. On a good day, it trashes your gearbox. On a bad day... well, that is what driveshaft loops are supposed to be for.
 
I think you could probably use a carrier bearing on the back front shaft, straight out of the Tfer case, carrier bearing before the U joints, then let the front shaft pivot as needed. No different than making a steering shaft with a carrier and multiple joints.
 
Edit: What in the world are you doing here? Rear shaft in the front, front shaft in the rear????

You may be on to something there, with the distances reversed that may not be a bad option, straight shot the rear and carrier bearing the front with the slide.
The way he has the rear now the slide is to far out to work well that way,and to stretch the front that far will definitely cause vibration without a carrier
 

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