Long arms and upper control arms.

[Dann]

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

[xj92]

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.

[azxjman]

I have seen the longarm setups with the stock upper shortarms and it basically runis the whole premis of the long arm.

[CW]

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.

[RCP Phx]

The castor change is much worse with stock uppers!

[Spooky]

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.

[vintagespeed]

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.

[Spooky]

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.

[RCP Phx]

The problem with that theory is that castor is not important when wheeling,pinion angle is!

[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

[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.

[vintagespeed]

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.....

http://www.rockxj.com/images/front_setup.jpg

:D

[vintagespeed]

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.

[mmyers]

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.

[CW]

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.

[vintagespeed]

Originally posted by mmyers
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.

If you like fully hydraulic steering then why not. :D

[vintagespeed]

Originally posted by CW.
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.

That's not exactly true. With a hi-pinion housing there is more than enough room to mount a lower link below the axle centerline. Lots of competitors do it this way. If the lower 'link' is in a parallel plane with the driveshaft how is it going to hit it?

Just 'cause Beez didn't go this way doesn't mean it's not possible. :rolleyes:

[Spooky]

Originally posted by vintagespeed
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.

The upper axle mounts are the original upper mounts on the axle. As the suspension starts to travel down the upper link will get longer and the lower will get shorter(relativly speaking) and rotate pinion angle up a bit. As it continues to droop the pinion angle will rotate down. from full extionsion to full compression it will rotate up to a point close to ride height then it will rotate down untill it reaches full compression.

If you will look at the construction lines if you go down 3 inches and back 10 inches(I actually have it as 8" on the drawing measured to the back of the yoke insted of the center of the ujoint hey it was dark) that is the center of the ujoint at the pinion end.

I corrected it here:

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


I also added the arms at full compression and pinion for all 3 positions. The crappy pinion angle at the level position is due to my RK arms limited adjustment. That position is the best compromise to keep my steering components out of my bracketry.

Not ideal but livable and should fix my bracket interference problems. I'll also feel safer with the 5 link.

Vintagespeed thats a sweet setup ya got there.

[vintagespeed]

Ok, the drawing looks good. I thought you were mounting the UCAs at frame height and the LCAs on the x-member like typical longarms? Have you changed to a more 'Tomken-esk' setup where the UCA is mounted in the stock location?

[Spooky]

I have not gotten a really good look at Tomkens setup so I'm not sure if it is simular.

The uppers will mount to the "frame" where the stock LCA brackets were in the same vertical plane with the factory UCA's but below them close to even with the bottom of the "frame" rail. I'll try to get them as low as possible without hiting the lower arms on compression.

The lowers mount just forward of the stock crossmember. Its standard RK long radius arm kit. I will probably keep the RK lowers and brackets for a while so I can spread out the cost. I'll just torch the tourqe arm bracket off the driverside radius arm if it gets in the way.

I like the way Andy Zuber builds his secondary crossmember in front of the stock crossmember on his radius arms. I May do somthing simular or I may Sleave the RK arms with some DOM tubing with a RE spherical bushing at the axle end and live with a 3/4 shank rod end and RK frame brackets but I'd rather have something a bit more beefy.

I figure JKS uppers with Curries axle mounted JJ's and lowers with some type of JJ' or Spherical bushing on both ends should eliminate most binding issues.

A corectly designed raduis arm would probably be better but ever since my tourqe arm bracket broke at 55mph on the highway(I got lucky) I have wanted more points of attachment to the axle and frame.

[vintagespeed]

:)

[vintagespeed]

Before you proceed to hacking, you need to do some more research and do a few scale drawings. Your 5link drawing isn't a representation of what you plan to do.

#1 the scale is way off, compare the UCA length to the distance between the axle mount locations.

#2 the UCA mounting location vs. the LCA mounting locations are not accurate. If the UCA is mounted below the frame in the stock LCA location and the new LCA is mounted above the frame on the x-member, then the drawing is way off.

#3 the UCAs will mount under the frame & the LCAs will mount inside the framerail on the x-member. This could lead to some contact issues during flex.

Basically the drawing doesn't represent your idea at all. Needs some work.

[Spooky]

#1 the scale is way off, compare the UCA length to the distance between the axle mount locations.

15-17inches depending on finalized UCA bracket location 15" in the drawing. I chose 15" to be consevative to be sure the lowers dont contact the uppers. All lengths are taken form my XJ with a tape measurer and divided by 4. (1/4 scale) There is no hacking to be done my LCA mounts are alredy gone for the Rockkrawler long arms I currently have on the jeep.

#2 the UCA mounting location vs. the LCA mounting locations are not accurate. If the UCA is mounted below the frame in the stock LCA location and the new LCA is mounted above the frame on the x-member, then the drawing is way off.

The LCA mount is below the frame just forward of the stock crossmember. RK LA kit.

#3 the UCAs will mount under the frame & the LCAs will mount inside the framerail on the x-member. This could lead to some contact issues during flex.

again the LCAs are below the frame rail just forward of the stock crossmember. I guess I'm not good at describing things.