shock mounting

[shanehill]

To get the shock length I need on the front, I need to mount the lower end of the shock below the lower control arm. I've got Ridetech 4.1's. The LCA has a 1/4" plate welded to the bottom. I could mount the eye above the plate on a trunnion but it will require a significant move of the upper mount AND the lower trunion mount would need to move inboard, therefore a big loss in motion ratio.

My original thought was to cut a slot in the plate and bolt a 5/8" trunnion straight up through the 1/4" plate and into weld nuts. But now my mind is rethinking this. All of the shock and spring forces would be across two 5/16 fasteners. A grade 8 5/16 fastener has a proof load over 4000lbs. Am I overthinking this? Even with a trunnion or fastener failure the spring will be captured by the lca arms and plate so the front wouldn't be able to drop very far.

My other choice is to weld tabs to either side of the slot and through bolt the eye using shock spacers. Easy enough. Just more work.

The third choice is to give up motion ratio, move the trunion to the top of the 1/4" plate, and extend the upper shock mount up a good bit.

For context, this is a 65 mustang with C6 spindles and Coyote in between the frame rails. It's NOT a heavy car. Figure less than 900 lb front corner weight.

Thanks, guys!

[SSLance]

A lot of experienced suspension guys will tell you they don't even like the trunnion mounts for a coillover. I watched an A body pull apart a tube on an inferior lower control arm this weekend on course and I guarantee that owner wishes now he would have chosen a higher grade part the first time around.

What is that saying.... If you don't have time to do it right the first time, when are you going to find the time to do it again?

[shanehill]

I get it. I'm not looking to take short cuts. But at the same time, if there's two ways to do it and both are equally strong, why do the long way. But if the consensus is that trunnions are not the way to go I can easily go the other direction. I actually have a set of 2" spacers coming from ridetech so I fab up a tab mount pretty easily.

[dontlifttoshift]

I would do the tab mounts, I avoid the trunions for all custom mounts whenever I can.

[bret]

When designing from scratch, I tend to prefer a non-trunnion mount, but that is just a personal preference.
Under NO circumstances mount the trunnion under the plate it WILL fail. That 4000 proof load assumes a perfect loading pattern, perfect torque, and a steady linear load. a large pothole that bottoms out the suspension could send a 4G load through those fasteners. Your 900 lb corner weight with a 2:1 motion ration would mean that coilover needs to support 1800lbs steady state. 4G x 1800lbs is 7200 lbs. Bad things will happen.

[DBasher]

Originally Posted by bret

When designing from scratch, I tend to prefer a non-trunnion mount, but that is just a personal preference.
Under NO circumstances mount the trunnion under the plate it WILL fail. That 4000 proof load assumes a perfect loading pattern, perfect torque, and a steady linear load. a large pothole that bottoms out the suspension could send a 4G load through those fasteners. Your 900 lb corner weight with a 2:1 motion ration would mean that coilover needs to support 1800lbs steady state. 4G x 1800lbs is 7200 lbs. Bad things will happen.

Dag nab it! One more thing I've got to change. Thanks for the info.