Shackle Angle

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74swangur

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This is a follow up to a recent post "Problem With Relocated Rear Springs".
Went by the local Dodge Dealer and spoke to a few friends I have there. They seem to believe there is a problem with my shackle angle. My Shackles are almost totally verticle(no angle). Shouldn't my upper shackle tube position through the frame, be forward of the rear spring eye when the cars weight is applied? If so how much?
 
the rear spring eye should be behind the upper shackle mount.......I have always been told about 1 -2" behind has been the rule of thumb I went by. I have made aluminum spacer blocks to "shim" out the factory mount so the angle was right. Your problem might be the springs are a bit to short since you swapped springs from another car. They might be arched to much....or you can move the hole in the frame forward more.
 
Dusterb318 said:
the rear spring eye should be behind the upper shackle mount.......I have always been told about 1 -2" behind has been the rule of thumb I went by. I have made aluminum spacer blocks to "shim" out the factory mount so the angle was right. Your problem might be the springs are a bit to short since you swapped springs from another car. They might be arched to much....or you can move the hole in the frame forward more.
Click to expand...

You got any pics of your blocks? I'm hoping I get more replys that say the same thing you said. (about 1 -2" behind has been the rule) :thumblef: :notworth:
 
This a pic of a set of blocks that another guy on Mopartech.net made (CheapstreetDuster) but it shows you what I am talking about. These will only work on a stock location though because if you relocated the springs the shackle uses the frame so a new hole will need to be made or a longer rear spring segment.

shacle_blocks.jpg
 
this was a shackle location of a stock spring car after converting/adding new SS springs.
the angle of the shackle doesnt allow for the spring to react.

p6110031.jpg
 
Well I'll tell ya....you launch your car with the shackle forward and the spring and the shackle will bind up. 90* or the spring eye behind the shakle is optimum. Start walking around the pits and look at the leaf spring cars and see where they have their shackles at.
 
:banghead: :finga: based on the link that "Ace" posted, 90*degrees is a goood starting point.

Quote from article:A good starting point for shackle angle is 90 degrees. In this position the shackle has no effect on spring rate. Keep in mind that the shackle angle changes (and consequently the spring's effective rate changes) whenever the suspension moves. Also, the shackle's angle will change whenever you change the chassis' ride height, the arch of the leaf, the load on the leaf, or the length of the shackle. Since the shackle direction changes when the leaf is deflected past a flat condition, you should avoid deflecting the right rear leaf to an extremely negative arch condition. This could cause a very large shackle angle at high loads and consequently a very soft spring rate. Excessive body roll and poor handling could result. You can correct this problem by decreasing the shackle angle, increasing the arch, of the spring by increasing the rate of the right rear leaf spring.
 
That is dead on. That article explains how shackle angle effects spring rate. Lets take SS springs for example. The shackle should be angled like I have stated above because as the car launches it rises up and the bottom of the shackle rotates forwrd and loads the suspenions which plants the tire. Then as the car moves down the track the suspension drops the car and the shackle rotates back to it's static position. If you would set up the suspension with the shackle in the opposite way when the car rises up on the suspension it would unload it causing loss of traction. So tell me which way should they be pointing?

leaf_4.gif
 
"The angle of the shackle can stiffen or soften a spring's normal rate. You can determine the effective angle of a shackle by drawing a line through the middle of both spring eyes and a line through the shackle pivots. Then measure the angle formed by the two lines (measure ahead of the shackle - see illus. 3). You can increase the effective rate of a leaf spring by decreasing the shackle angle. An increase in shackle angle will produce a decrease in the effective leaf spring rate of a leaf spring."

That is how the angle is determined....so with the spring installed in the car at 90* the shackle would be angled like I have described.....the top of the shackle forward of the bottom.
 
The first pic (rusty frame) you showed had it more right, the last pic you showed (chrome cover) had it more wrong. How this has anyting to do "spring reacting" I dunno. But what happens in the case of chrome cover car, especially if he is running stock or worn springs, is a severe case of wheel hop when the chassis unloads. I'm also wondering about the jackstand in the picture, because if the weight is off the suspension, none of this means anything.
 
That was my point......the second pic is how not to have them.......I thought I stated that but maybe I was thinking it but didn't type it. :drinkers:

As far as the jack stand I'm not sure if the car was sitting on it or not......like I said it wasn't my car or my pic...it was off another site and I posted it to show how they shouldn't look.
 
I have pick of the angle of my shackels on my site. I coundnt tell you what the angle is though, but maybe by looking at the pic it will give you a general idea.
 
I just do what the Mopar suspension manual says and it always works.
 
hi, just how thick is that block?? my shackles now are drivers side is +3 deg.(towards the front of car), and the passenger side is -3 degrees to the rear of the car, i guess what i am asking is how big a block am i going to need to move them to a -20-30 degrees or 1 to 2 inches?? this is on my 72 Plymouth Scamp/with S.S. springs.
 
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