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Discussion Starter #1
Well since everything is back together on the truck I can see how everything fits like it should. Apparently, the hole trick that seems so popular with Broncos and front hangers for a rear shackle flip, isn't quite proven with F150s. With the setup I'm running it's just a bit too much pinion angle. I don't *think* it's much but it's just enough to notice, would it cause any problems? Don't have any pix of it yet, but if I don't forget and can get some good light tomorrow night, I'll post a one or so to give you all a better idea.
 

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The F150's are longer so the driveshaft angle isnt as bad as the Broncos, which is why its a tad too much.

I got the same problem with my 14 bolt...I put the spring perches too far forward. I'm going to put a 1 or 2 degree shim under the spring pack to make it perfect.

-Will
 

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Discussion Starter #3
About how much excess angle will cause problems? Since I'm horrible with angles I'll say it like this: if the pinion were lowered maybe 1/4"-1/2" it'd point directly at the output on the transfer case, provided I'm remembering this correctly. Is that too much or is it too wide of a figure?
 

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Im not sure to be honest.

However keep in mind people run blocks every day with bad pinion angles an the only ill effects are ujoints that wear out quicker, and possibly vibration.

This angle is in the opposite direction but I"m not sure it matters. I wouldnt think so, but who knows.
 

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this link should answer any questions you might have about pinion angles.
 

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Like most others I've read, that link is wrong.

CV (or Constant Velocity) joints are a class of joint which are designed to eliminate the variation in angular velocity that plagues u-joints, thus they are given the name Constant Velocity. The simplest CV joint is simply two u-joints connected end to end, usually the center section is called an H-yoke because of its shape. In this manner, the angular velocity variations of one joint are canceled by the joint on the other end.
A DC is NOT a CV, in any manner, way, shape, form, context, or interpretation. This part is true:

What a double cardan will do, is split a universal joint operating angle into two separate angles that are exactly one half of the original angle.
That's the ONLY function of a DC.

He has an animation on that page that "shows" the variations, but I don't think it's technically accurate, either. Anyway: the H-yoke of a DC is exactly like the middle shaft of his animation, and its angular velocity fluctuates in the SAME way as the animation's. But since the DC is flexed identically at both ends (instead of reciprocally, like his animation), that fluctuation is transmitted to the main shaft, which in turn fluctuates TWICE as much as the H-yoke since it's got 2 flexed single-cardan joints affecting it. In the animation (with reciprocal flex), the fluctuation is cancelled out by the 2nd flexed joint.

A CV has NO fluctuations to cancel out - period. Its angular velocity is "constant". No joint that involves a cardan joint (U-joint) is a CV.

But back on topic... :D

The pinion should be parallel to the crankshaft/trans mainshaft/t-case mainshaft. The only exception is on Broncos, where the short d'shaft isn't heavy enough to cause a noticeable vibration, but misaligning the pinion is cheaper than having a DC at both ends of the d'shaft.

 

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Wow Steve, you are very touchy on that double cardon and constant velocity joint subject. The whole purpose of the link was to explain to Dave the principles of how a driveline works and I think it does that quite well.
When I had that vibration problem in my Bronco, I had driveline theory explained me by a mechanic, and I had trouble understanding what he was telling me until I found this site. The explanation at the site combined with the visual aid helped me understand what was going on with my truck, enabling me to fix the problem.

Double cardon, CV joint, it doesn't matter to me as long as the person I'm talking to knows what I'm talking about.
 

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Steve, I rarely find myself disagreeing with you, but in this case, you're 100% wrong on nearly all the information in that post.
Steve83 said:
Like most others I've read, that link is wrong.
...
A DC is NOT a CV, in any manner, way, shape, form, context, or interpretation...
Actually, as far as the shafts connected to the DC joint are concerned, the DC joint does act exactly like a CV. Let me explain ...

Steve83 said:
...He has an animation on that page that "shows" the variations, but I don't think it's technically accurate, either. Anyway: the H-yoke of a DC is exactly like the middle shaft of his animation, and its angular velocity fluctuates in the SAME way as the animation's.
Correct. Exactly like any other shaft between two cardan joints.

Steve83 said:
But since the DC is flexed identically at both ends (instead of reciprocally, like his animation), that fluctuation is transmitted to the main shaft, which in turn fluctuates TWICE as much as the H-yoke since it's got 2 flexed single-cardan joints affecting it.
This is where you're incorrect, and it's throwing off the rest of your thinking. There are in fact two arrangements of a pair of cardan joints that will cancel out the velocity fluctuations. One is with the input and output shafts parallel -- i.e. 5* down angle at the transmission output, 5* up angle at the pinion relative to the intermediate shaft, so that the total change in angle is 0. The other arrangement is with an angle between the input and output shafts, and that angle split by the intermediate shaft -- i.e. horizontal input shaft, 5* down at the first cardan for 5* down total in the intermediate shaft, and then 5* down at the second cardan for 10* down total at the output (pinion) shaft. Either orientation will cancel the fluctuations. In other words, it doesn't matter which direction the two cardan joint angle changes are, only that the angle changes are identical, and all three shafts lie within a single plane (in the case of a vehicle, usually a vertical plane, without also zigging sideways). The best link I could find handy with the equations for cardan joint motion is here, which appears to be a German site associated with Dana.

For a very common example of this second arrangement, look at the front driveshaft angles on any four wheel drive Ford. The angles usually aren't set close enough at the factory to completely eliminate front vibration because of other constraints, but the arrangement is within a couple of degrees and does minimize it. Moving forward, you have a down angle from a nearly horizontal front TC output, and a (nearly) matching down angle to the sharply angled pinion shaft, minimizing vibration.

Now, if you were to rotate the second joint in the DC 90 degrees (so that the yokes in the center intermediate member were no longer lined up to form an H), then you would get exactly the behavior you're describing, with the fluctuation in the output shaft twice the fluctuation in the DC intermediate member. The phasing of the two joints is absolutely critical.


Steve83 said:
In the animation (with reciprocal flex), the fluctuation is cancelled out by the 2nd flexed joint.
As it should be.

Steve83 said:
A CV has NO fluctuations to cancel out - period. Its angular velocity is "constant". No joint that involves a cardan joint (U-joint) is a CV.
As shown above, any combination of a pair of cardan joints working at the same operating angle within a single plane (regardless of direction of angle change) will transmit motion at a constant velocity.

Steve83 said:
But back on topic... :D

The pinion should be parallel to the crankshaft/trans mainshaft/t-case mainshaft. The only exception is on Broncos, where the short d'shaft isn't heavy enough to cause a noticeable vibration, but misaligning the pinion is cheaper than having a DC at both ends of the d'shaft.

Actually, the driveshaft angle arrangement on the Bronco is the only possible arrangement of three cardan joints which will cause no vibration at all. The first two joints in the DC cancel all fluctuations, and you can only get zero fluctuation at the pinion if the third joint is dead straight. Neither the driveshaft length, mass, or cost have anything to do with why this arrangement was used in the Bronco.

As for the rule about pointing the pinion at the T/C output, it's a "close enough" rule of thumb, but it isn't quite correct, nor is it the best way to set the pinion angle. What you're actually trying to go for is a pinion angle measured from horizontal that is about 1* below your driveshaft angle measured from horizontal. This is because under load you want the pinion shaft and driveshaft lined up dead on, or as close as you can possibly get it.

The combination of torque and spring flex lets your pinion shaft rotate upward under load (axle wrap), so what you're really trying to do is to optimize the angle of that third joint for one particular loading condition -- usually highway cruise, where you spend most of your time. At low loads the pinion will be down a degree, but not enough to cause a noticeable fluctuation. You rarely see very high loads (to the limit of traction) at very high driveshaft speeds, and cardan jointed driveshafts are more tolerant of misalignment at low speeds (smaller forces produced) where they see higher forces (in lower gears).

Make sense?
 

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here we go.
rebutle, Steve? :popc1:
 

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Discussion Starter #11
Ugh, you guys should not have posted that much tech in one post.....with reading that much tech at night letters start to melt together and I can't read a thing. But thanks for the info. :thumbup

No pix tonight, the ones I snapped didn't get the angle good, so they'll be coming Saturday.
 

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Steve83 said:
I'm too tired to think/type/argue this tonight. Lemme simmer...
No problemo ... gives me time to make certain I know exactly how these suckers work too. They look so simple, but when you try to actually describe the motion with equations, kapow! :shocked
 
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