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Help with reparing PTO drive shaft

8495 Views 5 Replies 3 Participants Last post by  DavCon
Me again..... can anyone provide a link to a site that will give me a little help with reparing the pto drive shaft?

What I'm looking for is a video or walkthrough on how to remove and replace a yoke of a pto drive shaft.

I hope I'm using the correct lingo here. :fing20:


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I had one last year that had the yokes of the U-joints welded to the telescoping tubes.

Just a word of caution if you do replace a yoke; pay attention to U-JOINT PHASING!!! My company installs motors and drive systems in industrial plants, and one of the mechanical engineers told me about this.

You can google that for a bit more info, here's a quick bit from an article dealing with truck driveshafts, but the principle is the same.

Incorrect U-joint alignment

If you've performed any lifting on your truck's suspension, there's a good possibility that the operating angles of the two joints on opposite ends of each driveshaft are no longer "equal and opposite". With the exception of driveshafts equipped with CV joints, this is the cardinal rule of driveline alignment.

This is hard to imagine, and even harder to explain, but here goes: when a common cross-cardan type of U-joint (a "Hooke's Joint") is operated at anything other than a perfectly straight alignment, the motion of the two halves is NOT identical.

Suppose, for example, that the "driving" shaft (from the transfer case) is rotating at a uniform 2,000 RPMs. The "driven" shaft (driveshaft) on the opposite side of a bent u-joint experiences a motion which AVERAGES 2,000 RPMs, but which ACTUALLY is speeding up and slowing down slightly -- twice per revolution. It's a NON-UNIFORM motion. (The math for this is available on request.)

This non-uniformity or variation in the velocity of the driven shaft increases with the severity of the operating angle. At 25-degrees, the variation in rotational velocity of the driven shaft is nearly ten percent. That is, for two brief moments during every revolution, the driven shaft is rotating at nearly 2200 RPM; and for two brief moments it is turning at only 1800 RPM. The driven shaft still AVERAGES the same 2000 RPMs of the driving shaft, however.

Ideal alignment is to reverse this process at the bottom of the driveshaft -- to input a non-uniform motion, and get a resulting uniform motion of the axle pinion. If the operating angle of the second joint is not equal and opposite to that of the first, however, a non-uniform motion of the axle pinion will be the result. Hence, driveline vibration.

If you're rolling down the road at a constant speed, and the engine/transmission is naturally trying to maintain a uniform motion, the two ends of your driveshaft are each trying to accomodate a DIFFERENT, non-uniform motion.

Corrective measures include tipping the engine/transmission or tipping the axle with tapered shims between the spring and axle -- with equal u-joint angles being the only cure short of a CV joint.

One final aspect of U-joint alignment that deserves atention is "u-joint phasing". Not only must the U-joint angles be equal and opposite (so that the speed variations are equal in amount), but also, the joints on both ends of the driveshaft must be oriented so that these speed variations occur at the proper time. Both yokes must be in the same plane. That is, if an imaginary dowel were inserted in place of the U-joint cardan on each end, the dowels should be parallel.
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Here's a little better explanation of what happens in a u-joint when it is working at an angle...
Thanks for the advise. Is there anywhere that I can look to see how to disassemble these? I have an existing one, but there is a set screw that is broken off and rusted in place. I want to replace it.
Is it the yolk on the end of the actual pto shaft?
If the set screw is rusted and broken just drill it out and then you can fight it off the shaft.
I think I found a site that will help me.

Haven't tried it yet, but it sounds like it will work. Stay tuned.....
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