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Discussion Starter · #1 ·
Trying to get my pinion angle set correctly for trip to the dyno.

If I understand what I have read....

The goal is to have the: tranny output shaft, driveshaft and rear diff. yoke all in a straight line when under load.

With no load, the yoke on the rear diff. should point down a bit with respect to the drive shaft so that when the rear housing rotates under load, the small no load angle becomes zero under load. Does this make sense?

Most of what I have read states that for a car with trac-bars, you need to set the pinion angle at about 5-7 degrees. This seems to suggest that you expect the housing to rotate about that much. If I did my trigonometry correct a 24' trac-bar with a 1" space would only rotate about 2.5 degrees. Not sure where the extra 2.5 to 4.5 degrees come from?

So finally the question: if you shim up the trac bar snubbers so that thay are just touching, what pinion angle should I use at the drag strip?




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65 Fastback:393W, G-Force T5, 4.33:1 Moser N-pro case / 31 spline axles, 4 wheel Disc


<font size=-1>[ This Message was edited by: jeffstar on 9/29/06 11:06am ]</font>
 

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you are thinking that the front half of that leaf spring stays exactly like it is in your drawing. actually it tries to bend itself into an "S". this was shown with pictures back in the early '70s. so imagine a little spring flex to use up a couple of degrees of your pinion down angle.

i think the ball park used to be 7-9 deg for stock type suspensions, 4-7 deg for ladder bars, 2-3 deg for 4 link suspensions. thats by memory, of course, & i am getting old. just suggested starting points.
 

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Discussion Starter · #3 ·
Dave

So if I shim the trac bar bumpers to zero clearance at the drag strip, does 2-3 degrees make sense?

Jeff
 

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Trac bars are not supposed to be touching. They are supposed to be set so that they allow the springs to begin to wrap up and then contact the snubber. That gives the tires time to bite and get some traction.
Driveline angles ....
I was taught that while the car was sitting with weight on the wheels the angle between the tranny output shaft and the drive line was the same as the angle between the drive line and the pinion angle. If the drive line is 4 degrees drop from the transmission output shaft then the drive line should be 4 degrees up from the pinion. Another way to put it is that the transmission output shaft and pinion are supposed to be parallel and the driveline angled between them.
If there is no angle in the joints they will be damaged. The bearings have to move to spread the load.
 

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You are missing the dynamic part of the equation. Your right that the goal is to have the pinion axis aligned with the output shaft, but under load as the original post suggested. Most slapper bar set ups need that 5-7 degrees negative, that is the pinion lower than the output shaft.

You can't have excess angles through the u-joints as they'll fail. An old trick is to clamp the front of the leafs to better control wrap up.
 
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