ponyracer1 said:
5. Removing the stock pass side upper mount, replacing it with a braced mount, prob. the ones sold by poly perf.
Are you only using one 'upper'? If so, why bother doing anything with the passenger side?
ponyracer1 said:
6. Lowers will be between 36-40 inchs long.
Still curious how you're going to fit this past the crossmember without stretching the wheelbase up front. Don't forget the fuel lines and brake lines run inboard of the frame rails there as well, and it's not a flat surface to begin with (there's a pinch seam that comes out perpendicular to the frame rail).
Also you need to consider interference from the frame rails at the area where the old LCA mount used to be. I had this problem, and my mounts were even more triangulated than yours, and lower.
Look at the area right where the frame rail starts to curve up to the spring mount:
That's not at full stuff, and like I said, you can see how much lower those arms mounted. The axle mounts are not a straight shot from the LCA bracket, they're triangulated outwards, which is why this clearance becomes an issue.
A little different view here:
ponyracer1 said:
Now here's my questions, I know in this design there's alot of force on the upper so I'm using the .250 wall for that as well.
1. Any problem going that thick on the upper? (It's what I have, also have dom 1 3/4 .120 wall)
Nope. Use the thicker stuff and you'll be fine.
ponyracer1 said:
2. How high does the upper mount need to be (ballpark) for this design. I read 9" of vertical seperation is a good place to start. Does that still hold true?
No. Axle mount vertical seperation on a radius arm suspension changes nothing as far as dynamic response. What it DOES change is the amount of force the 'upper' link will experience, and also how much binding there will be when articulating (not an issue with only 1 upper). Typically mounting the upper to the factory UCA mount on the axle gives decent results.
Changing the vertical seperation on the axle has a much larger effect on 3- and 4-link setups, where the instant center doesn't remain constant and there are a lot more considerations to be made for pinion angle change etc.
ponyracer1 said:
3. How far back would you mount the upper on the lower arm? As far back as possible and still clear everything or closer to the front? I read the flatter the angle the better which leads me to think farther back and raise it up as high as possible in the mount.
Correct. The longer you can make that upper, the less binding and the less leverage on the upper link. The specific
angle of the upper link in a radius arm setup again has no effect on the actual dynamics of the thing - that is more specific to the 3- and 4-link setups as mentioned above. However keeping the main radius arm (the lower) flat is highly beneficial.
ponyracer1 said:
4. How do you think the street manners will be on this design? Should be similar to a standard radius arm set up right?
Really depends on a few things. With a single upper you're doing the right thing in not using bushings, as this will keep the axle rotation during braking at zero. It also depends a lot on the angle of the arms - radius arms work best when they're as flat as possible, and if you're trying to tuck them up inside the frame rails, you may end up with some angle on there depending on lift height. What you'll see from that is increased anti-dive, which can give an interesting feel during hard braking (the front won't dive as much as you're used to) and also lead to increased unloading when climbing steep hills (= loss of traction under the front wheels, more weight transfer to the rear, less steering control, more likely to backwards roll). Again, this depends on your specific angle and it's likely that it'll be 'decent', and it's a simple solution that will help increase articulation and improve ride quality over short arms...but there's a reason why most guys on here graduate away from radius arm configurations.
My opinions on the setup I built/ran - it worked. The brake dive thing took some getting used to and got a little squirrelly in situations where I had to maneuver during heavy braking. The front end did tend to unload while climbing (this is REALLY obvious in videos I have of it) but the shocks were too short to allow full travel at the time, so that kept it under control (same thing a limiting strap would do, but less.....elegant?). Crossmember hung too low but I knew this when I built it and the whole thing was really a design experiment anyway, as it was the first one I had built.
Take a look/search for Timmay's recent buildup - he just did a nice radius arm setup on his DD XJ.
Does that all make sense?
