I was looking for input on the forward shackle setup in the picture of a 1964 Comet . I’m getting ready to put a similar setup in my 1964 Comet and was wondering if there are any pros and cons as to if the shackles should be in the front or rear of the spring . I’ve seen pictures of other cars with the shackles in the rear and liked the looked of this setup My car will be for street only with a BBF. Any constructive input is greatly appreciated Sent from my iPhone using The H.A.M.B. mobile app
I'm sure the engineers will chime in, but I think having the front of the spring fixed in a bracket would be a better way of keeping the axle vertical centerline in one place since the thrust would be mainly from front to rear. I don't think I've ever seen a rear axle have shackles at the front.
In another world I’m a jeep guy. Rear mounted shackles are supposed to give smoother ride and stability over the front setup. The front is said the have more axle shift to the rear. Im sure there’s alot of suspension knowledge here and someone else will clarify Sent from my iPhone using H.A.M.B.
Assuming you have a conventional side mounted steering box and parallel drag link, rear shackles will produce bump-steer to the left, front shackles produce bump-steer to the right. If you have cross steering like the car in the picture you shouldn't have much bump-steering problems. Otherwise should make no difference, it is just a room problem for which setup you choose.
I figure that you are only going in a straight line, but generally front shackles mean oversteer and rear shackles mean understeer for what it is worth. As a gasser, unless you get out of shape understeer is probably better than oversteer during panic mode... Just MHO.
The car will only be used for the street 99% of the time . It may find it’s way to the track 1 or 2 times a summer but that’s about it Sent from my iPhone using The H.A.M.B. mobile app
Ford F100 pickup trucks '53-'56 have the shackle at the front. These trucks had their steering box's drag link attached to the left side spindle. I believe the '48 up to '53 were also that way.
My Avatar photo shows you that they work with the shackles in the front. Car went in the 9's and unless the track was grooved like the old Savannah dragway it went straight every pass. I could not get down Savannah dragway track because they used the track during the week to haul dirt away from the old round track and the dump trucks wore ruts in the track. They were not noticeable to most modern cars, but old straight axle cars like mine ,it was a hairy ride. Just like ruts on the interstate that the semi's make. I just stopped going there ,it wasn't worth wrecking the car.
It all has to do with the angle of how the spring is mounted. The fixed eye should be at the same level as the axle [mounting pad] to create "close to vertical" suspension movement. But because the spring has an arch in it , to lower the fixed eye means the shackle end is raised. It is easier to have the shackles at the front with a Kick-up type frame rail.
I forgot to add one thing. A rear mounted "fixed eye" helps with anti-dive due to brake torque on the axle trying to thrust the axle downwards.[Induced negative caster] The spring should have an offset centrebolt, and the shorter side is always towards the fixed eye.
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