REAR END ANGLE

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I am putting together a truck for the first time and need to know what angle the third member should be rotated at, via the hiems from the wishbone. Screwing the hiems in or out changes the angle the drive shaft will attach to the transmission. It will have apox 30" travel. Any help please?
 

Timmah

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The pinion angle is important, but that angle is usually set in relation to the tailshaft/driveshaft angle. Assuming you have a one piece driveshaft, set the veh on level ground at ride height and measure the tailshaft angle and the driveshaft angle. the difference is the frt working angle. Try to make the frt and rear working angles as close to the same as possible, usually within a degree or so and that should do it. Some things to consider though; neither working angle should be zero and stock u-joints are usually not set at more than 4 or 5 degrees working angle for street use. For long travel set ups, I think you can stretch the limits a little to try and maintain a decent pinion angle thru all that travel, but the u-joints WILL bind at some point if you get too extreme on the working angle.

Hope this helps!

I LIVE MY LIFE ............ ONE CORNER AT A TIME!!
 
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Actually, what I have is the third member bolted to the rear end. Next I have a custom built drive shaft about 4 feet long. Last, I have a smaller drive shaft that bolts to the transmission end and is held up by a type of urthane shackle that bolts solid to the bottom of the cab. So what I think is the smaller shaft is in a fixed position do to the solid pre-exhisting mounts put there by the orig fabricator. So the actual drive shaft will bolt to the smaller one and directly down to the third member. But, I can rotate the third member by screwing in or out the heims.
So from what you are saying is put the truck at ride height and rotate the rear end with the drive shaft attached and that angle should be as close to the angle of the smaller shaft attached to the transmission?
 

Timmah

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Now that I know you have a 2 piece driveshaft, things change a little. There is a working ankle anywhere there is a u-joint. It sounds like from your description that you have a u-joint right after the center support. So now the two working angles that you will be concerned with are of course the rear and also at the u-joint right after the center support.
Set the veh level at ride height and measure the angle of the fixed end of the fixed end of the U-joint just rear of the center support and then compare it to the driveshaft angle for your frt working angle and then adjust your heims at the rear end until you get the frt and rear angles close to the same. Be aware that when you change the angle of the rear end, the drive shaft angle will change too, so you need to check the frt angle periodically as you are doing your adjustment since that is your reference point.
The only thing left to do is cycle the suspension through it's range and see how much pinion angle changes at the extremes, but that will largely be dictated by your 4-link design.

I LIVE MY LIFE ............ ONE CORNER AT A TIME!!
 
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