Long travel rear shock setup

[mr_blasto]

A long while back Greg72 mentioned the idea of using f250 shock towers for the upper shock mount in the rear suspension--the idea being to use longer travel shocks without inboarding them. I am about to put 1-ton axles in and I will be re-doing the shock mounts, so I got to thinking about this. I figure I would do the shock towers on the outside of the frame and have the shocks between the leaf spring and the tires. I will be using a D70 HD dually axle with H1 wheels and 13.5-15" wide tires. I am also going to be using 56" or 57" rear springs (I am having a hard time deciding).

As I am thinking this out, I would think that if the upper and lower shock mount were oriented in the same direction, as one side flexes the travel will be limited by the bushings in the shock. If the shock mounts were perpendicular to one another (one shock eye facing east and west while the other faces north and south, approx.), then the bushing would bind as the axle moves front to back while it flexes. How could I make this work / what am I missing here?

I really want to weld these mounts so that I can have a bunch of travel, but I would only inboard them as a last resort. No, I don't think I am ready to cut up my floors, but I do have a tiny body lift for what it's worth. What is everyone else doing?

 

[Greg72]

If I'm understanding your question correctly....the simple way to avoid binding is as follows:


Make sure that for each shock, you mount the upper "eye" 90* off from the lower eye....

Example:

If you use the F*rd brackets in the rear, then the bolt that attaches the upper shock mount will be PARALLEL to the frame (ie. the bolt runs front-to-back relative to the truck). Therefore, the lower mount bracket should be set up to that it's bolt runs ACROSS the vehicle (ie. parallel to the axletube).


This is hard to explain, but easy to see in person:

When the spring compresses, the shock will move backwards therefore you need freedom of movement in that axis. The LOWER mount would be setup to accomdate that since it's parallel to the axle tube.

In articulation, the shock is going to need to travel in an arc relative to the frame and that is where the UPPER mount will accomodate that motion without binding, since it's parallel to the frame.

Combinations of these two are still fine, because you have degrees of freedom in both axes and the only "twisting" will be the piston in the shock body as it moves, which doesn't hurt anything......


Does any of that make sense???

 

[mr_blasto]

Your description makes more sense than mine, though we were thinking about the same thing. Thank you.

As I am picturing this with the setup you mentioned (parallel to the frame for the upper, and parallel to the axle for the lower), I can see that the lower mount would pivot as the axle moves upwards and rearwards, but I still cannot grasp why or how the upper mount/bushing would not bind. It seems neccessary to have TWO pivot points working in the desired direction of movement rather than just one. The only answer I can come up with is that there is not enough articulation for the upper mount to be a factor, but with 57" springs, that would be hard to believe.

I don't get it.

 

[Greg72]

You're right about the upper mount....but I think it's a question of degrees.

You'd probably have to calculate the total change in position of the axle and see how much deflection that REALLY creates at the upper shock eye. Assuming that you set up the bracket at ride height with NO sideloads on it,then you'll get a small amount of tweaking under droop (axle moving forward) and a small amount under stuff (axle moving back)....

You could build a dual-pivot upper mount to prevent binding in EITHER axis, but I don't think if you drew out the suspension on graph paper and looked at the shock angles (even at the extremes) I don't think you'll find that they are going to be that bad.....certainly within the realm of what the bushing material can handle....

Prove me wrong though, I'm interested to see your calcs!

 

[mr_blasto]

You could build a dual-pivot upper mount to prevent binding in EITHER axis

I thought about that, but it might be more than I am interested in - it is a daily driver, and it needs to have minimal down time.

Prove me wrong though, I'm interested to see your calcs!

Nothing like a little challenge to motivate , thanks. Once I figure out how to make those calculations, I'll get on it. Thanks for your input.

 

[RGV72BLAZER]

i'm really interested in this topic b/c eventually i'll have to set up my shock mounts as well but i wouldn't mind cutting through the floor. what if i plan to run one ~45* towards the front of the vehicle & another shock ~45* towards the rear? would kind of help with axlewrap...

 

[mr_blasto]

I don't really have any sort of pics because the axles aren't under the car yet. I ordered the towers last night, so when I make some progress, I will let you know how it goes. I don't know about the asymmetrical setup, I would think there are better ways to prevent axle wrap, but I dunno.

 

[RGV72BLAZER]

...hmmm...

 

[hvy chevy]

I don't really have any sort of pics because the axles aren't under the car yet. I ordered the towers last night, so when I make some progress, I will let you know how it goes. I don't know about the asymmetrical setup, I would think there are better ways to prevent axle wrap, but I dunno.

Ever complete this?