1957 Chevy with a '57 Chevy truck axle, spring shackles in front or in back of spring AND why? On the truck Chevy must have spent a little R&D on this subject and decided to install shackles in front. I see gassers both ways. Pro's, Con's?
As you say, have been done both ways over the years. But, think about this - 1 - The "load" (from the road) is trying to push the wheels...backward...right. Therefore, "swinging" back and forth on the shackles. 2 - The "braking" action, is trying to push the wheels...backward...right. Therefore, "swinging" back and forth on the shackles. 3 - Any sort of wheelstanding, the "load" will try to push the wheels...backward, upon the landing...right. Again..."swinging" back and forth on the shackles. Who the hell wants the front axle moving back and forth on a swing set ? A thing to remember. The rear portion of the spring...IS...a spring, right ? It will bend...just as "springs" are meant to do. Again, the spring is NOT a solid member! So...do you really want the front axle flopping around on loose shackles...having a sloppy connection the frame in front, of the axle...or..do you want the spring held solidly to the frame (shackles in the REAR), so the axle will have a MUCH less tendency to move back and forth on the swinging shackles, therefore the steering will be, again, MUCH more solid, the braking will be more firm and connected to the ground. Personally, I'd NEVER put the shackles in the front. Mike
IF done right you will have some anti dive during braking if shackles are in the front. Where the steering box is and weather side steer or cross steer can be other factors.
I have them in the back of my axle. It has been like that since the sixties and works great. It was done for most of the reasons Mike VV stated.
I've always put shackles on the opposite side of the drag link. So if your steering box is behind the axle I put shackles at the front. Or if it's in front I put shackles at the rear. The theory is that the drag link pushes sideways as you turn the wheel, and it's better to push against the fixed eye end of the springs instead of pushing against the shackles that can deflect.
Every production car or truck the I can remember had the shackles in the front, there must be a reason the factory did it that way. If you have or know of a stock vehicle that has the shackles in the rear post it up. I have no knowledge of why they were built that way from the factory, so that would be interesting to know also if someone has real knowledge of why.
Ever seen a rear axle, with parallel leafs, and shackles on front ? Steering type and box location, would make a difference on front. I have seen it done both ways.
More theory but, I think typical frame side profile shape being usually higher (off the ground) in the very front (or very back) versus the mid section. That, combined with the typical shackle being taller than the typical solid mount makes placing the shackles at the outer most ends of the frame the most sensible. In other words, it’s typically easier to achieve a flat or level spring pad mount by placing the shackles at the outer most ends. I’m strictly looking at this from a mass production viewpoint. In the end, it’s whatever works for you.
If I'm not mistaken my O/T 78 f250 and 74 power wagon both have shackles at the rear, solid mounted at the front.
My '46 pokey bar pickup has shackles on the rear of the front springs...factory cross steer, box behind the axle.
Stock weren't cross steer, they were push-pull drag links with steering arms hanging down. Parallel leaf shackles for rear axles have little to do with front axle shackles. The side loads on a rear axle are simply generated by cornering, not by a drag link pushing or pulling. And the shackles at the rear have only small effect on steering geometry.
My Austin gasser had shackles in the rear with the factory setup. I also kept the shackles in the rear since I used a Corvair van box and cross steer in front of the axle. The stock steering was push-pull, so shackle location was really not relevant as it is with cross steer. And most old trucks with shackles up front were also push-pull steering, not cross steer.
Front springs should have a slight angle to rear; i.e. rear spring eye distance to ground less than front, absorbs road trauma better. Where you put the shackles can achieve that with a given frame design/contour. I put the axle in my Shoebox with the shackles in the front with cross steer box ahead of axle. I also have a panhardt bar. Power 605 box, works well.
The 4x4 brigade has big discussions on placement of the shackles and the reasons why but they may not apply to straight axle parallel leaf spring rigs. As for Chevy trucks from the 30's to 59 one big difference was the shape of the frame rail it's self. Even back to the 20's Chevy had the front springs solid mount on the front and the shackle on the back but the frame curved down to the point where the spring mounted. Come late 47 and AD trucks and the rail is pretty well straight to he end. Chevy cars had the leaf springs mounted to the frame at the front with Shackles at the back up through 39. Chevy trucks changed in 38 if not earlier. The GM Heritage Center archives don't show the leaf springs on the earlier rigs. These images from 38 to 57 skipping between 49 and 56. On a jacked up "gasser" with way more weight due to the weight of the axle it isn't going to handle all that great at any rate.
A simple cut and paste from the other thread i replied to: Rear shackles give a better ride. It allows the spring to "follow" the bumps in the road. The spring reacts and moves backwards as it travels thru the compression. A front shackle moves the spring forward into the compression. Yes it's not a lot of movement but it's enough you will feel it giving a somewhat harsher ride, look how many oem's still use a front shackle ? And the couple that do, do it because of clearance problems to the rear mostly. On a gasser it doesn't matter, your going 1/4 mile at a time on a flat surface, no rail road tracks or large pot holes to deal with.....
Unless your car is hitting very tall bumps like a curb at speed, the location of shackles front or back wont make a difference in how the springs compress. The axle moves slightly towards the shackle end is really so minor and the axle's movement is mostly up and down with very little directional change. If your axle has a panhard bar as Seb Fontan's car has it wont matter which end the shackles are on as the panhard bar negates any side deflection.
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