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Part of the confusion of pinion angle settings is that you are trying to take an educated guess at how much the pinion angle will change under load. The generally accepted change for leaf spring cars is 3-5* for auto cars and 5-7* for sticks. Obviously a high H/P car with soft springs will wrap the springs up more than a low H/P car with stiff springs, and a car with clamped front segments and/or slapper bars, Cal Tracs, etc may be only 1-2* deflection. And here's the rub - there's also u-joint operating angle to consider. And while on paper your car, with the trans pointing down 4*, you should need the pinion at 0*, so your leafs can let the pinion rotate 4* up to make the math for pinion angle work - that may leave your u-joints with no operating angle, (the engine/trans/driveshaft/pinion are all in line)and prone to fail from brinelling. That's why I mentioned that sometimes you have to change the engine centerline to correct the pinion angle. I'm sure there will be some that disagree, and this subject has been beat to death in the race forum. It may take several adjustments to get the whole package where you want it.

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Mr. Spirit,

A question for you so that I might learn no argue, are you saying on a street driven normal use street car you would set the pinion to allow for 4-5* wrap up on an auto and 5-7* on a stick? In the end at cruise speed I would think that the maintained torque/wrap would be the same for either one. Now in a holeshot/hard accel situation I could see the violent action of a stick wrapping up more and I could see a quarter mile car under constant accel until it's shut down sustaining a 4-5* wrap up. My specs were told to me long ago and I have set up many at 2* with no ill effects and to my knowledge never had to go back and adjust due to a vibration.

Thanks for your input.

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Your driveline could very well be "happy" with only 2* pinion angle, if the front spring segments don't deflect much under power, whether it's from a lack of traction or a from having a stiff spring package. But you can have a car that drives beautiful on the street with street tires perform horribly at the track with slicks, developing a vibration from excessive spring deflection ruining the pinion/u-joint angles. Leaf spring cars usually need some help to keep the angles in a happy zone, to keep the angle from changing much from cruise to high traction launches. Clamping the front spring segment, slapper or Cal Trac bars, etc. are ways to limit the change in pinion angle under power that doesn't happen with ladder bar or 4 link cars, not to mention the angle changes that happen as the car changes ride height under launch.

Keep in mind that leaf springs are a poor choice for rear suspension - a spring, by nature, is supposed to absorb, store and release energy - not what you want to transmit energy from the rear axle to the car, due to the spring trying to wrap up and flatten back out. They can be made to work very well with "crutches" to reduce their inherent problems - many times with a lot of trial and ERROR. Just be aware that with leaf springs the pinion and u-joint angles are at the mercy of how well you can match spring function to traction.

Again - this subject has been beat to death in the race forums, with many opinions on how to measure it or the optimum setting. The end result is the optimum setting that u-joints can live under without creating vibration varies greatly from car to car. What generally works is that while under power a slight u-joint angle and the engine/trans/pinion centerlines are aligned. How to achieve that is the fun part.