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Ca ???

FernXJ

NAXJA Forum User
Location
Cinci. OH
What kind of adverse effects would occur if the CAs weren't parallel? I'm not planning on changing their width apart at the axle. But, making them longer,still the same length ratio as now. And moving their mounts closer vertically. TIA, Rensing
 
I don't think that it matters that much. A lot of people have the lowers strait and the uppers like a triangle. Ao it looks like |/\| with the axle on the tip of the triangle.

edit: After I reread the post, I realized that I read it wrong. So, having the CAs longer I think would make the axle rotate different then normal. However I can only prove this with moving my arms.
 
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I was talking more on the lines of >. Open mouth at axle and point at crossmember. Not as severe as the symbol, but pulling the vertical distance between the two closer together, back by the crossmember.
It hard to explain.
Say UCA mount at axle is 40" from floor, LCA mount is 33" from floor at the axle.
Then, UCA mount at frame is 42" at frame and LCA mount is 38" from floor at frame.
Looking at the CAs from the side of the vehicle they look like >, but not as severe.
Thanks, Rensing
 
It's difficult to offer much from your limited description, but draw your proposed links in side view and you will see that you will likely be moving your instance center lower and forward. The closer you bring the upper and lower mounts together, the more your links will behave like radius arms rather than 4-links. Depending on your exact configuration, the result could increase anti-dive, resulting in a harsher ride and increase the rate of change in castor and pinion angle for a given amount of suspension movement. Neither of these changes are good if the majority of your driving is on the street.

You should take some exact measurements of each of the control arm pivot points and transfer the information to paper to draw a side-view of the links. Measure rearward from the axle centerline for X (horizontal plane) and up from ground level for Z (vertical plane). Do this for the existing linkage and the proposed linkage to compare the change in IC and effective arm length.
 
That's what I was hoping someone would write in on. Search is down on Pirates and I've tried here with little results.
I've found info. on Pirates before on the rear setup, but not the front. Do you have any links to front susp. setup.
The specs I listed before were just to try to explain. I wish I could send pics.
Thanks again, Rensing
 
I did a NAXJA search on "suspension + link" and it returned 86 hits. You can also try "longarm", "anti", "radius", "geometry" etc. Pretty much any term commonly used in a discussion of links should return some info. If you can't use the search on POR, browse back through previous threads in the General 4X4 or Jeep sections, looking at the topic headings.
 
OK, so you want to know if the lower control arms and upper control arms need to be parallel. Lets keep the numbers small for now. If the LCAs are 2 inches from the UCAs on the frame and the axle, then the axle will move up and down strait. However if the LCAs are 2 inches from the UCAs on the body and 1 inch on the axle, then the axle will rotate and will mess up the suspension. I tried it on AutoCad, and the "axle" rotated in odd angles. :confused1
 
Max- I've been reading over the link search. I'm really not trying to go with a radias arm. But, wouldn't the reaction of the susp. with arms not copletely parallel be better than full fledged radias arms.
It would still change Caster just at a slower rate. I would be looking at close to the same amount of bindage as the radias arms though. I wish I could use CAD to determine how much.
Reading all that Ed Stevens and yourself write steers me away from radias arms. But, if I end up using them there would be poly spericals and lack of the pass. arm. Unless I fab a new pass. upper backet to except the load.
Thanks again for the info. Rensing
 
FernXJ said:
Max- I've been reading over the link search. I'm really not trying to go with a radias arm. But, wouldn't the reaction of the susp. with arms not copletely parallel be better than full fledged radias arms.
It would still change Caster just at a slower rate. I would be looking at close to the same amount of bindage as the radias arms though. I wish I could use CAD to determine how much.
Reading all that Ed Stevens and yourself write steers me away from radias arms. But, if I end up using them there would be poly spericals and lack of the pass. arm. Unless I fab a new pass. upper backet to except the load.
Thanks again for the info. Rensing

Parallel aren't necessarily something to strive for. The upper and lower arms on a stock XJ are not parallel. They converge at some point rearward, defining the instance center. This is where suspension inputs react with the chassis. 3 and 4 link designs allow more flexibility in locating the instance center. Radius arms or (long arms) react with the chassis at the control arm mount. Less flexibility in design, but a reasonable compromise and a definite improvement over short 4-links at large lift heights.

You should define where you are currently, and the associated problems you are trying to resolve. Then you can set design goals, typically a better street ride, more flex, more clearance, etc.

You mentioned that you want to build long arms attached at the cross member. What are you trying to achieve?
 
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