Well, thank you all! I have very mixed ideas now as a result of the many responses. I guess I am just going to make sure the wheels look right and are the same distance/space from both sides of the frame rails. Of course, this will make my pumpkin and pinion off from center and I will only need a 14 inch drive shaft, so I am still a little concerned, but thanx for all the responses, they are food for thought. Pork
14" shaft with how much pinion offset? 1" offset at 14" length will put about 4 1/4 degrees angle at the horizontal plane through that. If that's what's goint to happen, I'd build the ch***is to have the engine/trans--driveshaft--pinion to all be at the same angle in the vertical plane, meaning looking at it from the side of the vehicle. Overlooking the ch***is is where you'll see the angles going through the u-joints. If it's more offset than the example, you'd be far better off to use a diff with a centered pinion BECAUSE IN THIS CASE the driveshaft length will be so short. If it was a longer car it would not matter quite as much. 1/4" at 12", actually .240" at 12" equals one degree change. All about the math before you fab.
Common Ford differential and axle ***embly found in may production cars and half ton pickups from 1957 to 1986, even identified by Ford as the nine inch rearend based on the diameter of the ring gear. But not all cars or ttrucks of the previous description had a 9" from the factory. Many variables, many aftermarket pieces for drag racers, dirt car racers, etc. I hope you weren't serious.
cl***...CL***... thank you... U-joint physics. It doesn't matter which end you start from but starting from the ****** yoke, looking at the first ujoint, you have 2 of the 4 ujoints endcaps firmly attatched to the yoke. I'll call them caps a1 and a2 The other 2 ends are 90 degrees to the first 2 and I'll call them b1 and b2. b1/b2 rotate through the same circle as a1/a2 if the driveline is not angled but angle the driveline and not only do b1/b2 swing through a different cir***ference than a1/a2...b1's distance from center is different than it's compliment b2 so, they both swing through different cir***ferences from each other. These cir***ferences are not even circles. they are oval a1 and a2 travel in circles b1 and b2 travel in orbits that swing in to center and back out in 180 degree intervals. Complicated as it sounds without a diagram to illustrate the geometry the end result is that a1/a2 are driving b1/b2 through a constantly changing geometry which causes the drive shaft to turn faster then turn slower than the yoke driving it. put it on a clock diagram with a mark on 1 of the ujoint caps to point to a time and you could say the yoke and driveshaft are spinng the same speeds at 12:00 and 6:00 but the driveshaft is spinning faster than the yoke at 3:00 and slower than the yoke at 9:00. Why don't you feel the vibration? because the angles at the other end of the driveshaft are equal but opposed 180 degrees so the accelerating/deccelerating driveshaft now drives the rear yoke at a constant speed equal to the front yoke. In a 3 ujoint 2shaft system like a longbox pickup the first shaft is in line with the engine/****** so it is at a constant speed. if not there would be no compliment to cancel the geometry variance unless you added a double cardan joint to one end. The center of the double cardan joint acts as another driveshaft. When driveline angles cannot be set up to cancel each other out the double cardan or constant velocity joint is employed. Think I'm wrong about ujoints? ask yourself why something other than a 4 trunion ujoint is called is called a constant velocity joint. If your engine is inline with the ch***is and the rearend is square then you only need to worry about pinion angle in the vertical plane. use a carpenters protractor with a bubble level to find the angles. set it on the machined flats of the yoke straight up and down. extreme...if the ****** points down 45 degrees from plumb the pinion must point up 45 degrees from plumb. real world... if the ****** points down 10 degrees the pinion must point up 10 degrees. It doesn't matter if your taking the angle measurement in line with the driveline or 90degrees to it from the ends of the yokes. You can point the centerline of the axle pinion at the ****** ujoint like when lifting a 4x4 to the extreme and have 2 different driveline angles IF you employ a cv or double cardan joint.
if the rear end pinion not being in line with the engine confuses you... look at the driveshaft angles from the side then look at the driveshaft from the rear now put one of your ears against your shoulder and look at the pinion offset... OOOOOh sidewaysie is the same as up and downy why wouldn't it be. relativity rules
Measuring off of the frame you may find out later that everything is not quite as square as you believed. I learned the string method after doing it the wrong/easier way several times.
Good to have another member that understands. This driveline angle stuff can lead to much misinformation and many arguements. PM from anybody that needs help with problems like these are welcome. Math before welding is always good. Do the driveline guys need to build something for the technotronic library? If so, I'd like to part of it with Torchman too.
I would agree. establishing a benchmark requires one point to draw from as a standard. one stringline down the center everything is pulled from is a true center and everything can be squared from that. a right triangle is one with a square corner Use a square or use the 3-4-5 rule. a-squared plus b-squared = c-squared 3*3=(9)plus 4*4=(16) equals 5*5=(25) a right triangle with 1 square corner and one side measuring 3a and the other measuring 4b will have a hypotenuse measuring exactly 5c. to make the triangle bigger or smaller just multiply any number by 3,4 and 5 so you want to check a 12' line's angle with another for square??? lets make it 3 times bigger 3(3)=9 4(3)=12 5(3)=15 so a right triangle with sides 9 and 12 long will have a hypotenuse 15 long lets make it half sized 3(.5)= 1.5 4(.5)= 2 5(.5)= 2.5 this is how you can square up your axles from the centerline
thanks Teach...uh i mean Torch for the theory lesson,one ques left to ask..."How many licks does it take to get to the center of a Tootsie Pop"?
would'nt that technically be called the Pythagorean Theorum? A squared plus B squared equals c squared?
More complicated math stuff that when it boils down, it's so darn simple. I was fed this in one day in high school and learned so much. I didn't realize and and remember where some of my math comes from until prime shot that in. Pythagorean's Theorum will teach in so may ways. Body height and waist size to equal where you shold be in weight. Why a mollusk shape is, foundation of that theorum. Math before sparks and metal changing.
Only to human perception. Up, down, left, right, don't matter to the driveshaft. It goes from point to point. On its plane of existence there is only one operating angle. From the output/input to the shaft. If the engine or rear axle are not parallel, then the driveshaft can't operate in a single plane, and will vibrate, since the u-joint angle of rotation don't cancel each other out. In the real world, slight misalignment keeps the needles moving without causing a noticeable vibration.
Bingo with what I don't know how to show. Parallelism is critical in a single two u-joint driveshaft situation with some variance. Dirt cars, drag cars throw out part of this. Cancellation is produced when the drive end u=joint angle is complimented by the same at the driven end angle with some small window of variation. Driveshaft rotation accel and decell twice with every revolution happen smoothly with every trans output and pinion input because of this simple complicated math.
In response to the original post. Yes you can center the housing with no adverse problems if the verticle angles at the ******, and the pinion are the same, but opposing. In order to center the housing, it's going to be nessessary to, at a minimum, shorten the right side axle tube and axle. The rest of the project will be dependent upon what you want to end up with on axle flange to flange measurement. Centering the housing has been done by axle builders for custom applications for years with no adverse effects, including mine. Don't worry about it, and enjoy your build!!!
patric2965, relic, prime and the torch.........you guys done good. The reason GM puts equal length axles in most of their rear ends is the cost saving of having the same part number, and the tunnel don't matter if it's offset in the vehicle as it's usually under the seat cushion height. U-joint cups have a small angle designed-into rotate the rollers otherwise they push thru the lube and "Brinnell" that's when you see that rusty powder in a joint that has been too straight. patrick, I'll be sending my driveshafts to you! 32rats***........thanks for bringing this thing to a happy conclusion.
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