Shackle flip and rear pinion angles

[1986c10]

Hi, i picked up a 95 chevy ecsb a few months ago. id like to lift it and have been reading up alot about rear shackle flips and id like to try it out. In my thinking though, if a shackle flip were done to the rear spring mount, it would drop only the rear of the springs and the front mount would stay in the same location. Wouldnt this drop to only the rear mount change the pinion angle of the rear end drastically? Or am i over thinking it? Thanks in advance.

[special-K]

I would think it would retain a more correct angle compared to a spring or block lift. Picture it as the axle housing simply pivoting on the front hanger,as the springs are designed to do in normal suspension cycling.

[1986c10]

well my thinking is with like a block lift, the stock pinion angle is retained because the axle is not moved any direction but farther below the springs and is not tilted any direction, just lowered so the 3 degree range between output shaft and pinion angle would be kept true. in a shackle flip setup, the eyehook of the rear part of the leafspring is lowered by 5-6" and id think that the lowering of only the rear would make the perches of the axles sit at a much different angle then stock... You probably are correct as many companies make this lift with no problems, i just wanna make sure before i dive into anything

[SunSoaked]

Originally Posted by 1986c10

well my thinking is with like a block lift, the stock pinion angle is retained because the axle is not moved any direction but farther below the springs and is not tilted any direction, just lowered so the 3 degree range between output shaft and pinion angle would be kept true.

Actually, just moving the axle down does change the pinion angle. It is pivoting around the output shaft of the fixed yoke (t-case or otherwise) on a long arc. The lower the axle goes the steeper or greater the angle. Think of the opposite. If you lift the axle to the same height (assuming diff is parallel) as the t-case, all the yokes would be in a straight line aka-zero offset. The further the axle moves down the more the pinion on the diff needs to be raised to maintain the same angle in relation to the t-case (or fixed pinion).

[Mr. 250r]

My brother used ORDs shackle flip in order to get rid of the block and it ended making his angle just right but he also has shims and he thinks it moved the axle forward that's also with a slip yoke 205 so I guess on a fixed yoke it would stay in the same place
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[1986c10]

I see what youre saying but correct me if im wrong, if the rear were lifted but the angle of the pinion stayed the same. The angle between the pinion and driveshaft as well the output shaft and driveshaft would be increased but the actual angle of the pinion and output shaft would be the same because neither were tilted. And from what ive been told, the angle of the pinion to the driveshaft and output to the driveshaft shouldnt be over 7 degrees and their shouldnt be more than a difference of 3 degrees between the two.

[1986c10]

Thanks for the input so far guys. Reading back, my stuff sounds really confusing. I'll try to draw some crappy pictures and upload them to help illustrate what im saying haha. Thanks

[Prerunner1982]

As Mr250r said... use 2* or 3* shims to get the pinion angle straight again. No reason to over think it...

[SunSoaked]

Originally Posted by 1986c10

I see what youre saying but correct me if im wrong, if the rear were lifted but the angle of the pinion stayed the same. The angle between the pinion and driveshaft as well the output shaft and driveshaft would be increased but the actual angle of the pinion and output shaft would be the same because neither were tilted. And from what ive been told, the angle of the pinion to the driveshaft and output to the driveshaft shouldnt be over 7 degrees and their shouldnt be more than a difference of 3 degrees between the two.

I think the angle has to change. Its the relation between the attachment points on each end that matter. Put a digital angle finder on your head and note the angle while sitting on the couch looking at the center of the TV. Now stand up and looking at the same spot see if its different. I'm betting when standing your chin is lower (assumimg your eyeballs stay fixed in their sockets..lol). The fixed yoke on the t-case represents the TV-it never moves. Your mellon represents the diff-it only moved up (or down). The angle of your eyes HAD to change in order to maintain the relationship or you would be looking at the top (or bottom) of the TV.

Kind of cheesy but hopefully illistrates my point.

[Psycho71]

The shackle flip does help retain the pinion angle better than a block or spring lift. Simply vertically relocating the rear end does change the front and rear yoke angles. But, like stated above, the shackle flip uses one attach point, and rotates the entire axle to provide the lift.

I used diy4x's shackle flip kit w/their cross-tied shckles to get a 4" lift in the rear. I don't regret it a bit.