I've been doing a little reworking on my Model A chassis. I've got a Ford 9" rear that has the pinion offset from the center of the rearend. Do I need to be concerned about the misalignment between the tranny output shaft(which is centered in the chassis) and the pinion? I'm assuming (hoping) that as long as the engine tranny centerline is perpendicular to the rearend that I'll be o.k.???? What's the reason for offsetting the pinion anyways? Thanks.
You are correct in your thinking. All will be fine. The factory probably offset the pinion to run the driveshaft straight for economic reasons. As long as the offset angle on the tranny output shaft is equal to the offset angle at the pinion you should be fine.
Yes....the rearend must be perpendicular to the engine/tranny centerline. Your U-joint angles shouldn't exceed 3 degrees. Multiply the length of your driveshaft (center of front yoke to the center of the rear yoke) by .05234 (sine of 3 degrees). If the result is less than the offset you should be O.K. Example : 36" long driveshaft X sine 3 degrees = 1.884" (36 X .05234 = 1.884) If the offset is less than 1 7/8" you win ! This is true in both views...side view and top view. If you exceed 3 degrees in the U-joints they'll wear faster and might create a vibration. Don't know why the pinion is offset.
[ QUOTE ] I'm assuming (hoping) that as long as the engine tranny centerline is perpendicular to the rearend that I'll be o.k.???? [/ QUOTE ] yep! you're fine.
oops, guess I'm too late, its funny how the post sits there for 20 minutes and then gets 2 responses at the same time, then one from me 2 minutes later.
Thanks guys. That's the answer I was hoping for. It sounds like I'll be well under the 3 degrees SJFast. I can finish off the tranny mount tonight and hopefully get everything painted this weekend. Thanks again.
I read this and started thinking. If your pinion is offset 3deg to the side, you could probably run the pinion and engine at zero degrees tail down. I don't know why you would want to but in theory it would work. TZ
Yeah. This was info I needed too. I suspect that your nine inch came outa a Ford Bronco. From what i understand this was to provide clearance for the front facing driveshaft. I didnt even notice till I got mine in the car. Then it was WTF? I kinda figured if a driveshaft can be off in one direction, why not two?
the u joint will fail if it is working in 2 angles. they are only ment to work in one direction. most rear end pinions are offset to the passenger side for driver clearence. chevy and fords off set the motors almost 2 inches towards the passenger side. i went threw a long debate over this with 3 chassis builders when setting up the jag rear in my car.(offset 1.5 inches to the right) to make it work with out problems i had to put the crank in a perfect line with the pinion with the drive shaft only angled in one direction. if you angle both directions you will have premature failure. sorry to be the one to say it but a broken u joint can really hurt you and any one around it.
here is a bad rear set up that broke and cause the truck to flip. you can see the drive shaft works in both x and y angles
Slag, i'm not seeing how what yer sayin' makes any difference. Technically, it's still only one angle, it's just that the plane that the pinion-to-driveshaft angle is on gets tilted in this situation. If what you say is true, then you's hafta always keep the car level, no? (You wouldn't be able to drive on any roads that have a "crown" to them!) As for the offset pinion, a lot of people that use the 9" rears will narrow them such that it centers the "bulge" for the 3rd member between the wheels. This is especially true for Model As since you can see the rear without looking under the car. And the difference between the lengths of the axle tubes becomes much more apparent when the rear's housing is narrower. Now that the "bulge" is centered, the pinion has to be slightly off-center to properly mate with the ring gear. At least that's how I have seen it done a couple times. I have known a couple guys that had this setup, and claimed no problems with the drivehaft offset, but they were chainers that didn't drive their cars nearly as much as they ought!
yes it can work in that pic with it only working in one angle but that pic it is working in both angles.
That's how I recall it also, per Slide. Imagine your car is hung on two pivots, one on the grille, one on the back bumper. You're standing looking at the side of the car, you slowly turn the car and eventually the trans and pinion shaft become equidistant to your eyes, i.e. the plane they define is perpendicular to your line of sight. That is the view at which you measure the single driveline angles. Was that Geometry? in which we learned, once two objects are parallel, they will always be parallel regardless of how they are moved as a unit in space?
This comes up so oftren maybe we should have a permanent post on the subject. First, a u-joint is made for the express purpose of running at an angle. Second, a u-joint that runs perfectly straight will wear prematurely. The needles NEED to roll on the trunions or they will Burrnell (imbed) into the cross. There is hardly a car made the the driveshaft runs straight down the center (parallel to the frame rails). If you doubt it just place about a dozen cars on a hoist and look for yourself. Besides the u-joint angles change about 100 times a minute while you are driving. Frank
fab32 is correct. There must be some offset. Another thing to consider is compound off set. Say, using my 36" driveshaft example in a previous post, that you have 1 1/2" offset vertically and the same amount horizontally, then the total offset would work out to the hypotenuse of a right triangle with two 1 1/2" sides (vertical and horizontal).That third side would work out to 2 1/8" (2.121") and would exceed the 3 degree angle in the joints. Just another thing to consider....
I suspect you have more than a drive line angle problem that caused your truck to flip. I may not know everything when it comes to Jag rears, BUT only using one shock on a stock lower dog bone is a recipe for disaster! Those bones were designed to have load on both sides and if you remove one of them it causes a twist in the 'bone and will lead to premature failure. I have seen that happen before. Now the angle of your drive line does look excessive, and the drive line looks pretty short. A few more before and after pictures might tell a better story of what really happened. As to the point of the post/thread. Pinion offset is no different than is pinion hieght differences. So long as your joints are in phase and the angles cancel out you will be fine. SJ is on the right track with degrees, I would say no more than 3degrees for maximum strenght but I belive most drivelines could handle in excess of 8 degrees. There is plenty of information from Inland Empire's web site as well as this nifty links page to some definitive answers, Inland Empire drive line set up links page
[ QUOTE ] Don't know why the pinion is offset. [/ QUOTE ] Most all manufacturers play with pinion location for chassis fitment. Like in the instance of the 1957-1966 Ford trucks, both axles are the same in lenght therefore requiring an extreme offset in pinion. Even though the engine trans was on CL. Some times you will see the carrier centered with a slight offset to the right on the pinion. This is done to balance weight distribution on the unsprung (sometimes total) wieght. Both horizontal and verticle planes of static angle need to be considered. With the extremes of some of the "rat rods" around here you have to watch the angles at total compression also. Here are a few more articles for you reading pleasure! http://www.novak-adapt.com/knowledge/driveshafts.htm http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml http://www.classictruckshop.com/driveline.asp Here is a great one, On topic too! http://www.drivetrain.com/driveline_angle_problem.html
When I stated that I don't know why the pinion is offset I was referring to his particular rearend choice. Every application is different for various design reasons.... Your last link pretty much backs up what I was saying. I was attempting to keep the explanation in simple terms. I have the advantage of designing my stuff in Autocad so, before a tube is ever put to the bender or the Portaband begins slicing up any steel, I have some assurance that this junk is all going to fit together correctly. It ain't rocket science....but there are some basic rules that need to be followed for the best results.
[ QUOTE ] the u joint will fail if it is working in 2 angles. they are only ment to work in one direction. [/ QUOTE ] Having the crank and pinion offset vertically and horizontally is of no consequence whatsoever so long as the total UJ angle is not excessive. Grab a piece of writing paper, lay it landscape (long side horizontal) then make a fold about an inch from the bottom, fold again, and repeat until you have a strip about an inch high by 12" wide. Apply a piece of tape or a couple of staples on the last edge to prevent it springing open. With a marker pen draw a line about an inch long close to the top fold starting from the left side, this is the gearbox shaft. Draw another line close to the bottom fold starting from the right end, this is the pinion shaft. Draw the diagonal line between them representing the driveshaft. With the strip lying flat on the table you have car with zero vertical offset and 1" horizontal offset. Tip the strip up so it is sitting on the long edge. You now have a car with one-inch vertical offset and zero horizontal offset. Tip the strip backwards so that it is half way between vertical and horizontal. Look down from the top and you can see about 3/4" horizontal offset; and with your eye down at table level look horizontally and see there is 3/4" vertical offset. Throughout all of this the gearbox shaft, driveshaft and pinion shaft remained in a single plane, and the angle of the UJ remained the same so for operational purposes they were the identical. Providing the gearbox and pinion shafts are parallel, then even if they have vertical and horizontal offset there will always be some plane in which they have a single offset. If this was not the case every time a racer ran on a banked track there would be drive shafts exploding into the crowd. There is however one point to remember. If you have horizontal offset and vertical offset, the total offset is larger than each of them individually. So when you check the UJ angle, use the total offset. How do we determine the total offset? Let T = total offset H = horiz offset V = vert offset Then T= square root(V x V + H x H) If for example V = 4 and H = 3, T = sqr rt(4 x 4 + 3 x 3) = sqr rt(25) = 5 If you are in the workshop without a calculator and want to determine the total offset, draw a triangle with the bottom side of length equal to the horiz offset, and the vertical side of length equal to vert offset. The length of the sloping side will be the total offset and can be measured off your triangle directly without resorting to any mathematics. Try it with the offsets in the example above. Then providing T is less than (shaft length)/20, the UJ angle is under 3 degrees and you will be fine.
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