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  #1  
Old September 5th, 2003, 14:32
Dann Dann is offline
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Long arms and upper control arms.

Has anyone used adj. UCA's in their stock mounting points with a long arm LCA set-up? I know the standard practice is to mount the UCA's to the long arm LCA's, but that results in caster change as the suspension cycles through its arc of movement. It would seem if the UCA's were retained in their stock position, with heims or johnny joints, you could maintain proper pinion and caster angles as the suspension cycled. I am assuming this isn't done because it would limit travel and articulation, but the question I have is how much. Obviously everything is a compromise and I'm not an engineer, so... I'm sure someone on this board has tried it, and I'm curious as to the results.

Thanks, Dann
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  #2  
Old September 5th, 2003, 14:51
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xj92 xj92 is offline
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The Tomken kit and the Teraflex kit do exactly that, use long LCA's and short UCA's in the stock location. I think the caster would still change a little bit since the lower and upper arms will be pivoting on a different arc.
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  #3  
Old September 5th, 2003, 15:10
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azxjman azxjman is offline
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I have seen the longarm setups with the stock upper shortarms and it basically runis the whole premis of the long arm.
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  #4  
Old September 5th, 2003, 15:15
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I am in the prosses of building long arms, and I a have been driving for four days with long lowers and stock uppers. It solved my death woble, but doesn't flex quite as good as just short arms. Once I finish the radius arms I will gain a lot of articulation. I don't think that the caster change due to drop on a radius arm set up is that big of a deal, because you are moving slow.
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  #5  
Old September 5th, 2003, 16:33
RCP Phx RCP Phx is offline
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The castor change is much worse with stock uppers!
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  #6  
Old September 5th, 2003, 17:35
Spooky Spooky is offline
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I'm about to ditch my Rk radius arms to do this. I'm having a set of upper control arm brackets built that will weld on where my stock lower control arm mounts were.

To keep castor more constant through your range of travel you will need to lower where your UCA's attach. You will get some really nasty pinion angle changes through your range of travle if you utilize your stock UCA mounts.

take a look at full tractions TJ lift ad in one of the rags and you will see what type of angles you will need to utilize to pull this off.

I'm planning to run JKS uppers with currie's axle bracket mounted JJ's and some custom lowers the same length as my rk arms with RE spherical bushings on both ends.
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  #7  
Old September 5th, 2003, 19:27
vintagespeed vintagespeed is offline
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Before you go whacking your Heep, take a piece of paper & draw your arm ideas to scale. Take a compass (thats the thing with the pencil on one end and the sharp point) Now take that there compass & make the arcs your arms will move through from their fixed point on the body end. You'll then see how drastic the pinion/caster change would be. If you go that route buy lots of front ujoints.....you'll need them. My 3 arms are equal length BTW and the body mounts are 1/2 the distance apart as the axle mounts = proper geometry.
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  #8  
Old September 5th, 2003, 19:34
Spooky Spooky is offline
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Already hacked LCA mounts are gone for the radius arms. Drew it to scale and its a lot less drastic pinion angle and castor change than using stock UCA mount locations close to constant castor. Should be livable.
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  #9  
Old September 5th, 2003, 20:25
RCP Phx RCP Phx is offline
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The problem with that theory is that castor is not important when wheeling,pinion angle is!
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  #10  
Old September 5th, 2003, 22:43
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David Taylor David Taylor is offline
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Jb, when will we see if it all will work. How am I supposed to know what springs to get if that thing never gets out of the garage. I'm counting on you for some good R&D.
Dave
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  #11  
Old September 5th, 2003, 23:49
Spooky Spooky is offline
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I'm not aurguing that castor is more important than pinion angle when wheeling. Just that pinion angle change and castor change will be less drastic if you lower the UCA mounting point from stock in a 5 link with long lowers. I'm tired of my swaybar links and stabilizer bracket geting hung up in my drag link and constantly bending brackets and drag links. I also want the added security of a 5 link.

here is a drawing at 1/4 scale from measurments taken from my xj wit rk radius arms and 6.75" of front lift illistrating at rest and at full droop. 28" lowers , 15" uppers, 33" driveshaft from joint center to joint center.

http://community.webshots.com/album/88156478rbjAfb

last photo on that page

While pinion angle is not ideal at full droop it is at a livable angle of operation for U-joints IMO. Please feel free to change my mind.
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  #12  
Old September 6th, 2003, 01:02
vintagespeed vintagespeed is offline
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Quote:
Originally posted by David Taylor
Jb, when will we see if it all will work. How am I supposed to know what springs to get if that thing never gets out of the garage. I'm counting on you for some good R&D.
Dave
It's getting close Dave, I'm still working on the steering. I've gotta install all the brakes during the week & maybe DRIVE it out of the garage next weekend.....



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  #13  
Old September 6th, 2003, 01:13
vintagespeed vintagespeed is offline
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Quote:
Originally posted by Spooky
I'm not aurguing that castor is more important than pinion angle when wheeling. Just that pinion angle change and castor change will be less drastic if you lower the UCA mounting point from stock in a 5 link with long lowers. I'm tired of my swaybar links and stabilizer bracket geting hung up in my drag link and constantly bending brackets and drag links. I also want the added security of a 5 link.

here is a drawing at 1/4 scale from measurments taken from my xj wit rk radius arms and 6.75" of front lift illistrating at rest and at full droop. 28" lowers , 15" uppers, 33" driveshaft from joint center to joint center.

http://community.webshots.com/album/88156478rbjAfb

last photo on that page

While pinion angle is not ideal at full droop it is at a livable angle of operation for U-joints IMO. Please feel free to change my mind.
Not to be critical of your drawing, but you need to draw in the pinion/ujoint point & note the yoke angles. I'm also a little unsure of your axle mounting method? If you lower the UCAs like you mentioned it will make it more acceptable (I missed that the first reply). The shorter upper arms will travel in a pretty tight arc and will rotate the housing backward putting pressure on the ujoint. The driveshaft angle is not relavent, it's gotta point at the axle what IS important is the ujoint angle at the yoke.
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  #14  
Old September 6th, 2003, 02:38
mmyers mmyers is offline
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Y style radius arm work good if you fab a crossmember and mount the arm close to center. The axle will pivot around the center mounting, and not induce axle twist, as does the Y style in the "stock" location.

Keep your track bar to alleviate bumpsteer. A 4 link front is horrible for that.

I'm also toying with an idea of making a trussed front with a pivot bar that would extend to roughly the stock upper location. With the traditional style Y, the baem would pivot, and eliminate axle twist, while maintaining rotational control. Heh!!

M.
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  #15  
Old September 6th, 2003, 12:33
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CW CW is offline
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You can't mount your lowers in the center. The drive shaft and exhaust are in the way. Read a few of Beezils posts about his wishbone project.
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