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Old 01-14-2006, 10:36 AM
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pinion angles make my head hurt

im setting up the rear end in my 48 chevy truck , i read thru some old post and some magazine articles. i get the angles being equal but opposite, 3*seems to be the best place to start. do i set the rear end 3*up or 3* down the information Ive got, one says up,one says down

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Old 01-14-2006, 11:21 AM
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Its not up or down that you need to worry about. Lets say the tranny is level, that is to say the tranny's output shaft is at zero degrees. The pinion should be at zero degrees also. Equal and opposite means the angles on the driveshaft, not the pinion or tranny. The pinion angle and the tranny angle need to be on parallel planes, like in this first photo



If you set up the pinion and the transmission angles on parallel planes, the driveshaft angle will be equal and opposite. The driveshaft will come out of the tranny, angle down 3* for instance, and then angle back up 3* at the pinion. The 3* figure comes from the fact that you should have some angle in the driveshaft. When setting it up, just take your cue off the transmission. Measure its angle. If its up one degree, point the pinion down one degree. Then you measure the driveshaft. The angle between the tranny and shaft will be equal to the angle between the pinion and shaft since the pinion and tranny are parallel. If the pinion points down one degree and the shaft points up two degrees, that's a total of 3* If you want more or less, adjust both the tranny and pinion equally. For instance, if you want that number to be 4*, shim up the tranny for another half degree up, and put the pinion down another half degree.

The optimal 3* number is not the pinion angle itself, its the angle of deflection between the pinion and the driveshaft.

Here's another reference for you;
http://www.iedls.com/ptsetup.html
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Old 01-14-2006, 11:33 AM
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Imagine if you draw a line through the crankshaft, and draw a line through the pinion shaft, they should be parallel. THEN compensate for axle wrap by pushing the pinion shaft down the specified amount for your particular suspension type. Four bars get the pinion shaft angled down in the front from this "parallel" alignment from 0 degrees to 1 degree. With leaf springs you compensate for axle wrap with about 2 degrees of pinion angle. All settings must be done with the weight of the car loading the suspension. Here is a link that may help. http://www.carcraft.com/howto/91758/
This is how you would do a car that has a driveshaft that the u-joint operating angles do not exceed 3 or 4 degrees. If you have a situation where the angles are greater, (lifted/lowered alot, really short driveshaft), then you have to do things a little differently. Hope this helps, Mike
ps nice diagrams in your chart, curtis73, those really help to explain things.
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Last edited by powerrodsmike; 01-14-2006 at 11:40 AM. Reason: compliment curtis73
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Old 01-14-2006, 12:02 PM
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thanks for the reply,

Last edited by CARGUY; 01-14-2006 at 12:10 PM.
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Old 01-14-2006, 02:23 PM
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A friendly ammendment if I may The compensation for axle wrap is a very wise drag race choice, but on the freeway it might make a serious whine or vibe under neutral accleration. I like to set up my street cars just straight up parallel with the tranny output.

It also depends on what type of suspension. A trailing arm suspension with spherical rod ends won't have any measurable deflection, but a leaf spring axle will have more. I fully agree with your assessment and I'm not arguing, just an additional opinion.
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Old 01-14-2006, 08:29 PM
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Curtis73, I respectfully would add this thought: I would want to see how many leafs were there , I agree, 2* compensation may be a little more than what a street car or a truck with a big stack of leafsprings would need, But take out 3 or 4 leaves from the stack, (not uncommon when doing old trucks), and figure in all that frontal area that a truck has and there is bound to be at least a little spring wrap at cruise. I think there is really no good way, (that I know of), to tell what the ideal angle would be for a given car, other than to set it up close to what you think is right for the suspension type/construction and driving style then fine tune it as needed. 2* compensation for leaf spring wrap is not an uncommon place to start. I think that the first words in the car craft article I posted says alot:
How To Set Pinion Angle
Ask 10 Guys About Optimal Pinion Angle And A Lively Debate Will Ensue
I am not looking to debate with anyone though, I only want to share information. I think that we have both given information that is well within the acceptable range. You never know what a person will accept either. I had a car on my rack one time that had the pinion 15 degrees up from optimum. The guy said he never noticed any vibration. He did say he replaced u-joints alot though. I aligned his pinion angle for him. He said it felt like a new car after that. Later, mikey
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Old 01-14-2006, 09:56 PM
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Old 01-14-2006, 11:56 PM
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thanks for the info, im just trying to get pointed in the right direction. i don't have the motor and trans mounted yet, i think ill do that first and then finish the rearend.
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