Theres been a lot of discussion about pinion angle lately. Here is what i know from a lot of racing experience. This discussion is just about the pinion, pretend the driveshaft is a string connected to the pinion. When we pull on the string it has the same effect as a spinning driveshaft. When a car takes off under power the pinion wants to come straight, pull on the string. A hard launch, pull on the string harder. If the pinion is pointing downward (negative, i believe is the term) when you pull the string the pinion comes up to point twards the source of the tug on the string (tranny tailshaft), when it pulls up it is pivoting around the contact patch of the ring gear. Since the pinion is pointing down the contact patch is above the pinion yoke (i don't know how to do those fancy dwarings so imagine looking at a pinion side view, the yoke end runs downhill from where the teeth contact the ring gear). When you tug the string the pinion yoke rotates upward around the contact patch of the ring and pinion and that action forces the rear end to rotate downward. When a car has negative pinion angle and launches it'll drive the rear tires into the asphalt, hookup and go. Conversely, if the pinion is pointing upward when you pull the string the yoke is above the contact patch so that the pinion will rotate downward round the ring and pinion contact patch and the rear end will rotate upward trying to lift the tires off the pavement. The harder you launch the more tire spin you'll have, just like a mustang - hint, hint. The string analgy is closer than you might think, when the driveshaft spins it wants to come dead nuts level - mess with a gyroscope, same thing - and when you lauch it gives the yoke a vicious tug. That should give you guys something to ponder.
I'm pondering and now my head hurts. I think string theroies should be applied to guitars and such...
Your string ideas do not clarify the issue, The base of the carb sits level, the angle of the end of the transmission equals the pinion Simple
Also dont forget no matter what to check your springs. The more they are worn the more they will through your pinion angle nuts and give you some funky vibrations under power and deceleration. Thats one major over looked problem that i see alot of.
I don't think that describes the phenomenon at all, even by analogy. There is no tension to speak of in the drive shaft, as all live-axle set-ups short of a torque tube will have some kind of slip connection to allow for changes in the distance between the gearbox tailshaft and the pinion shaft as the rear suspension moves. If not for that there would be only one allowable arc for the rear suspension to move in, and both launch and cornering behaviour would be severely compromised from the start. The pinion angle thing is better understood when you plot the movement of a point on the circumference of the tailshaft or pinion shaft in relation to a corresponding point on the drive shaft (I somehow don't think this'll be much clearer ) If the angle between the shafts is zero the movements of the two points will always match as the shafts turn; as soon as there is an angle between the shafts the second point will trail behind the first for some of the rotation, then catch up and overtake, then fall back again, by an amount that depends on the shaft angles to one another, repeating the cycle every 360°. The result is that, while the tailshaft turns at a constant rate, the driveshaft's rotation speeds up and slows down with every rotation by an amount that depends on the angle of the shafts to one another. If the angle at the other end of the drive shaft is the same, the mechanism will be reversed and yield a constant rate of rotation at the pinion shaft. And this holds whether the angles are in opposite directions (Z) or in the same direction (U), as long as they are in the same plane. If the angles are not the same, the speeding-up/slowing-down will be only partially eliminated, and the remaining inconstant rotation will be felt as a judder in the rear axle which is not only uncomfortable but represents a hammering on the ring and pinion, and consequently on the axles, axle tube, and suspension. One last thing to remember is that the angles might be perfect at ride height but deviate at other states of rear suspension movement. Just something to be aware of and to keep in mind when setting up rear axle locating devices etc. I hope that explains it once and for all. Why don't people just run CV joints on drive shafts? They're more than up to the torque you're likely to throw at them, having to live under first-gear multiplication in powerful front-drivers; there are enough of those around that they're quite affordable; and they'd make the whole pinion-angle debate disappear in a puff of smoke.
I just knew Ned (Dawie) would chime in. And what he speaks of is true enough. Except! at the moment of launch - if the driveshaft etc is in constant motion what is above is true. You don't like the tug of my 'string', well, try this. Unhook your driveshaft from the pinionyoke and let it lie there. At rest it will dangle from the end of the tranny - nothing to support it. Fire up the motor and put the engine in gear and that driveshaft will snap straight, hard and true. If is it nicely balanced you can reach over and touch it, push it and it'll come back straight and true - a long gyroscope that is level irregardless of the engine angle, the angle of the car etc. It is at the moment of launch that i am speaking, that millisecond when the driveshaft - from rest, layin on the ground or in your car - that it receives power. At this moment in time nothing has rotated, the .006 clearences in the gear lash is taken up and the next thing to occur is that lever action thru the pinion angle/relationship as the driveshaft snaps straight. All of this happens befor the driveshaft begins to rotate - we are speaking in less than milliseconds here. The rear end moves up or down before the car goes forward. I am not speaking in terms of maybe..or what if..or well, gee whiz..this is what happens every time you let out the clutch. Once the vehicle is moving the dynamics are completely different and Ned described them as well as anybody. I am trying to give you guys a little insight, you've got hot rods and traction or lack of is very important and traction has a lot to do with pinion angle.
Yep. This helps augment the wheel-hop you get from leaf-spring windup. The driveshaft is basically the 'cage' in a big CV joint. And sometimes there's other resonances that play into the situation, too. The '04-06 Cadillac CTS-V had a nasty wheel-hop problem, which could be counted on to break diffs, axle CVs, etc. The aftermarket was trying all kinds of solid subframe bushings, etc. but Cadillac decided it was axle-shaft windup, and in the current V they fixed it by making the axle shafts a little different torsionally - one shaft is solid, while the other is hollow but larger in diameter - so that they will wind up and release at different rates. Thing launches straight and smooth now. They do - it's very typical on newer vehicles. And, for reasons of packaging, NVH, and driveline critical-RPM, you find very few newer cars with one-piece shafts - just about everything has a center bearing and U-joint. Hopefully no more embarrassments like the Thunderbirds and Lincoln Mark VIIIs limited to 110mph by one-piece driveline whip. The setup you'll find on, say, a BMW with IRS - rubber guibo at the front, Cardan in the middle, CV at the diff - isn't really applicable for a stick-axle car, but I've got a cute little shaft in the shop that came out of an '08 GT500 Mustang. Cardan at the front (set up to run at a minimal angle), big CV in the middle behind the center bearing, and a CV pretty much identical to BMW practice at the rear. I'm hoping to use something derived from it in my '64 wagon.
I'm wondering what sort of gyroscopic force we're looking at, though, especially compared to the magnitude of the car's inertia, weight transfer, etc. I don't think it's really big enough to make a difference. In fact everything about the drive shaft is trying to make it as little of a flywheel (gyroscope) as possible and still handle the torque. The quest there is for that sweet-spot diameter where you've got the greatest torsional rigidity for the least weight for the least rotational inertia. Smaller and you need too much wall thickness and hence weight to handle the torque; bigger and the shaft will either be too delicate to be practical or too rotationally inert. Interesting observation, though, oj. Have you read up on bicycle theory? Similar results as regards the role of gyroscopic effects: you think they'd be more important. But it's hard to think how the theory behind something as simple and obvious as a bicycle can make one's head hurt as much as it does! (Also interesting is the way it wasn't in the least necessary to understand bicycle theory to invent the bicycle. We've had bicycles for considerably more than a century and have got them to work extremely well, but we still don't know exactly how we did it. It just goes to show how an entirely mythical rule of thumb can serve admirably in real life: something engineers can do well to remember.)
Just for kicks I did some measuring,52 ford f1 stock height no dush bags. With a 302 ford level carb it sits at 6 degs,not 3 degs and from there is a staight line out trans to rearend still out 6 degs,and the 9 " rear looks level.So under power if the drive shaft lifts say 3 inches at most with a 60" drive shaft, the angle goes to 3 degs and the trans would encrease to 1.5 degs maybe 2 degs. I,m not having any problems and don,t have a angle dangle tool. Days when spring would twist they used drag bars to stop that. With these dush bags i would think there is to much travel.
So ask yourself...how many banzai starts do I do a week? How much spring wrap occurs cruising at 70 MPH on the interstate? Are you building for the strip or building for the highway? Level the carb base at ride stance, measure the angle at the tail shaft, make the pinion angle parallel to that angle, weld the rear end in place and drive the sumbitch. I've never experienced any drive line problems in any of my builds over the years doing it this way but I'm not a drag racer. If you are constantly doing hole shots with sticky tires then disregard this post.
Simply put. All things being in good working order. 2.5 to 3 degrees on the drive shaft for a street car and 5 or so on a drag car (because there is more axle clime) If there is a vibration under heavy acceleration then you need to adjust up or down. Miller tools use to have a cool little drive angle gauge that had a magnet that stuck right to the u-joint cap. Remember the reason you have any angle in a drive shaft is so the bearings in the u-joint turn a little or they will flat spot.
I remember back drag racing and when the springs would twist to much it would brake off the u joints.Those old 50 fords ujoint weren,t very good then came the 9"That 57 ford with the 9" you could burn rubber a day and have no problem.
Hi, I think the problem always comes from having two correct answers to the question "What is the best pinion angle?" The best pinion angle for a car that is not raced is equal and opposite of the transmission angle, this will minimize vibration and wear. The best angle for a race car is 3-7 degrees down, so under max acceleration the driveline angle is zero, and the rotational force of the axle can be harnessed to transfer wieght via four link, traction bars, ladder bars etc. Both answers are "correct" so choose based on your application. Rick
oj, you should know better by now. Anytime you post a serious, well thought out tech question on the hamb, the result is a great gawd almighty cluster fuck...
Forgot two constraints on those answers: a) one-piece driveshaft b) semi-elliptic leaf rear suspension Take away either of those and I don't think they fit so well.
I'd like to see a video of that one. Methinks you're going to be buying a new driveshaft, some new floor sheetmetal, etc.
Might agree with a) but definately not b). I have run 5 down on a GM coil spring car, worked very well.
It IS horrible. 5 down, some power, a decent converter, and some sticky tires can lead to wheels up launches and broken teeth on your crown gear. And that'll play havoc with the fuzzy dice and cry-baby dolls. oh the humanity!!
If you want to learn very little on pinion angle and how to properly set up your driveline, research the subject on the Hamb. Read every thread, absorb all the information that all contradicts itself and every other post. Try really hard to understand complicated things like gyros and strings Realize that you will never get back the part of your life you just wasted. Wind up with a huge headache, swallow a couple aspirins and head out to the garage and build the darn thing. Use what your old buddy who has been building rods since the days of Noah told you. Set the carb base level. This makes transmission point down about 3 degrees. Set pinion angle up 3 degrees to make the trans output shaft and pinion shaft line up with each other and call it done. Move on to other parts of the build without looking back.
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