Shock Mounting Orientation?

[vengeful]

Hey all. On my Pathfinder, the studs that act as the upper rear shock mounts are in not so good of shape. I was considering welding a set of the JKS Shock Conversion Mounts onto my truck to replace the corroded and inherently weak studs. (4WP# JKS9602). Since the studs are, well, worn out, I was considering redoing the rear shock mounting completely.

Nissan built the truck with about a 15 degree from vertical towards the rear angle on the shocks. I figure they must hav done this for a reason...

Is there any reason should leave the shock angles alone, or are there specific advantages to having a vertically mounted shock?

 

[ntsqd]

The best situation is when the damper moves exactly the same distance as the tire. This gives the best control over the tire.

Then reality sets in. There are lots of reasonable reasons that this is actually rare to find. One big one is that with the damper mounted at an angle the damper stroke can be shorter for the same wheel travel. Which makes it easier to fit under the truck (both the angle & the length) and makes it cost slightly less.
There is a range of mounting angles where it essentially is straight up and down & I would venture that 15* is nearing the outer limits of that, but w/o doing a motion development I'm not sure.

Then consider that the leaf spring will move the axle away from it's fixed end as the arc flattens out in compression. Some folks think that the best mounting is to position the dampers such that they are vertical when the suspension is at full bump, which usually results in them leaning back when at rest.

 

[vengeful]

Leaf spring flattening? No worries there! The Pathfinders have a 5-link coil rear suspension.

I'm reading from your reply that under ideal conditions, I want the angle of the shock at ride height to be as close to tangential with the radius-of-travel of the wheel (which, due to the fixed length of the control arms is not a straight line, but rather an arc)? This is what I had figured, but I want to be absolutely sure that I'm not going to totally destroy my trucks handling characteristics...

 

[ntsqd]

Ah! I'm, obviously, not very familiar with Nissan products.

With linkage things get harder to put in words. Any linkage has an Instant Center (IC), the virtual center of the arc at that point in the travel. The IC can and will move around as the suspension cycles. To duplicate the leaf sprung mounting I mentioned above you'll want the damper to be perpendicular to the imaginary line from the axle housing centerline to the IC when the suspension is at full bump. Let the position of the damper at other locations fall where ever it does. What this does is yield a mildly rising damping rate. Meaning the valving gradually gets stiffer as you approach hitting the bump stops.

Now the caveat; this assumes that you're frequently using the full possible travel of the suspension. For a more OE-like ride I'm not sure what you'll want. It could be the same, or it could be significantly different.

 

[slomatt]

Since the damping force exerted in the vertical-axis is dependent on the angle of the shock, mounting shocks designed for the factory orientation at a higher angle will cause them to provide different damping than intended.

Of course as mentioned this gets difficult to calculate since the amount of damping will change as the suspension cycles through an arc.

- Matt