How much shock mount reinforcement is required to support a coilover on a car with separate springs and dampers?

Question

There are no off-the-shelf coilover options for the rear of my project car (solid rear axle, separate springs and dampers), and I've seen warnings from various car-related forums about attaching a shock/spring combo to the lower shock mount. This seems legit -- it looks a little flimsy to be supporting all that weight:

But I confess I don't know if that's the only safety concern in terms of points of failure.

Is there any reason I can't just reinforce the lower mount with a bolt-in or weld-in bracket and then use a "real" coilover with it?

Another option would be some kind of axle-mounted bracket:

On a related note, this would probably change the mounting angle of the spring/shock by +/- n degrees, so will that also introduce new issues with the top mount? I haven't even done anything yet, and it's already snowballing.

Answer 1

I am an engineer, and to cut to the chase: No way! It won't handle the forces, the geometry will be completely wrong, and the axle will not be located properly and constantly want to twist.

Your better bet is to figure out a way to incorporate the damper inside of the of the existing spring, and using the lower spring perch already on the axle. Only that area is strong enough and located properly to handle the forces that suspend the vehicle.

Another possibility is to have an expert welder cut away the lower sprint perches on the "donor" axle, and securely weld in the style of brackets you show in your picture - in the exact same place (the fore/aft centerline of the axle). That takes care of the lower coilover mount, but the upper can't go just anywhere and also has to be of suitable strength.

Keep in mind if you are installing a soild axle to deal with a larger engine with more HP/torque, you are also going to need trailing arm(s) or at least a snubber to deal with axle twist - something the factory body/suspension was most likely not designed to handle.

A panhard bar might also be needed to deal with left/right axle shift.