J Arms Vs. Mid Arms

[Goatman]

Can you give me a guesstimate as to how much the arm moves in relation to the center of the tube from fully compressed to fully drooped?? Do you think we're talkin about an inch? or 3? I'll have to sit down at the drafting table and have a look see. Does Currie's site have dimensions of the arms on it, if not, could you give me some?? Thanks

Ary

Look at your own suspension when fully flexed, those arms move a lot! I bet it would be at least 3" with a J arm.

 

[XJJPR]

It would be more for me because my arms are even with the axle, but I can see how sometimes they would just move out of the way by rotating sideways. It would be tough to build a set because they need to be so thick, I'd have to buy Currie's and lengthen them.

Hmmm, that would give me about a 26" long arm.

Naw...then I could be accused of having long arms.

I use to bend some of them for Currie when they were .25 thick, now they went thicker and bigger od so I don't bend them anymore.

You're like PS where he moved both ends of his arms also. Or he is like you, you did yours first.

mark
orgs mfg

 

[CRASH]

Actually, Rich, by lengthening the lowers and keeping the uppers OEM length, the pinion rotates more than stock. Not saying it matters, but it does rotate more.

CRASH

 

[XJJPR]

Actually, Rich, by lengthening the lowers and keeping the uppers OEM length, the pinion rotates more than stock. Not saying it matters, but it does rotate more.

CRASH

I'll be playing with that part later, but the pinion change (better than raidus arm pinion change) doesn't bug me that much. The 3 arms setup works good.

crash your wife wants to use the computer so go cook something.

hinkley

 

[Safari Ary]

Ok, I just ran outside and had a look-see. It appears that if I were able to push the axle ends of the J-arms towards the diff about 2-3" on each side(or maybe move the coils outward a little as well, maybe a 1/2" per side, since the new axle is a little wider) I could clear the coil perches altogether. Now since I'm a newbie to suspension design, I'm wondering what adverse affect this might have on ride/handling/stability, etc. The main problem I see is interference with the trackbar on the front side of the axle, but since I'm at least going OTK or maybe even hi-steer, that will have to be addressed anyway. Also, if there are any adverse affects, would doing anything to the uppers help?? Like pushing them towards the diff as well, or maybe towards the coils??

Also, Mark, how many uppers are you running with this setup??

Edit, you answered that while I was replying

If all these types of question are answered somewhere already, just point me there and I'll be more than happy to stop pestering you guys with pre-answered questions. Thanks

Ary

 

[XJJPR]

Ok, I just ran outside and had a look-see. It appears that if I were able to push the axle ends of the J-arms towards the diff about 2-3" on each side(or maybe move the coils outward a little as well, maybe a 1/2" per side, since the new axle is a little wider) I could clear the coil perches altogether. Now since I'm a newbie to suspension design, I'm wondering what adverse affect this might have on ride/handling/stability, etc. The main problem I see is interference with the trackbar on the front side of the axle, but since I'm at least going OTK or maybe even hi-steer, that will have to be addressed anyway. Also, if there are any adverse affects, would doing anything to the uppers help?? Like pushing them towards the diff as well, or maybe towards the coils??

Also, Mark, how many uppers are you running with this setup??

Edit, you answered that while I was replying

If all these types of question are answered somewhere already, just point me there and I'll be more than happy to stop pestering you guys with pre-answered questions. Thanks

Ary

You're kind of heading down nomans land or land of don't want to try all that. Sounds like a lot of work making everything else work to save a little ground clearance. The diff side really is no biggie and the other side no biggie either in my book. But I see the J arms as an improvement to clearancing rock (sliding over) from the stock setup. No Goat and Paul have done other work to get more clearance.

But you're just going to have to mock it up and see what everything looks like for room for everything else.

I'm running 3 arms. two lowers and 1 upper over diff. It has 2 2.5" jj on it. Frame bracket and axle bracket are changed. You can see both in the pictures, I think.

mark
orgs mfg

 

[Goatman]

Actually, Rich, by lengthening the lowers and keeping the uppers OEM length, the pinion rotates more than stock. Not saying it matters, but it does rotate more.

CRASH

The assumption is that the geometry allows for a minimum of axle rotation. The more the axle rotates (pinion) up, the less advantage the longer (front mounted) J arm has. As the axle rotates the J arm mount is lower than a normal arm would be, meaning more arc was traveled relative to the axle tubes and relative to a normal arm, decreasing the benefit. Of course, with a much shorter upper arm the pinion should rotate down, not up.

Have to draw the whole thing out with different length arms to see what would be ideal. It's an interesting scenario, and would need to be thought out well.

 

[Jes]

Bah, let's just go wheeling. Hammers anyone?

Jes

 

[Goatman]

Bah, let just go wheeling. Hammers anyone?

Jes

I'm just hanging out (didn't work today)........and listening to a very good album. Thanks....

Hammers.......I'm ready. Sun Bonnet, OL, and what else? I still think up the backside of Jack and then down Sledge would be a fun run. Clawhammer Friday night?

 

[CW]

How much does the pinion angle mater when you are moving at .5mph? Unless you are binding uni joints and grenading driveshafts when the suspension drops, how much difference does it actually make? This just isn't one of my top priorities while doing a suspension.

 

[Jes]

I knew you'd enjoy that, gotta listen to it loud.

Ya, that sounds like a good itenerary. I haven't done Sun Bonnet or Clawhammer(I think those and Upper BJ are the only ones I haven't done).
Also I hear Backdoor has been extended beyond the sand hill climb.

Jes

 

[RCP Phx]

I'll be playing with that part later, but the pinion change (better than raidus arm pinion change) doesn't bug me that much. The 3 arms setup works good.

hinkley

I have "Almost zero" pinion angle/length change with my Long arms.Until you can get a decent length upper to make it work,this seems like alot of work just to flatten out the control arm angles.The axle is still traveling thru the "same radius" but not thru the extreme levels of a stock set-up.

"its just a drop bracket kit inverted and reversed"

 

[Goatman]

Jes, I figure we'll save Upper BJ for BOTW......and I wouldn't mind another shot at Backdoor.

Did you walk UBJ? It's badass!!!

Yeah, no one home.......

C.W. As far as pinion angles, it's in the context of the J arm discussion, where it could mean a great deal. Also, if you're designing a link suspension, you better think and plan for pinion angle, and for pinion angle change. If you get too much change it will tear up your bushings when articulating because each side of the axle tries to have a different pinion angle......the only thing to give is your bushings.

 

[MaXJohnson]

Beyond what Richard mentioned, here's another tidbit to consider:

If you disregard changes in pinion anglewith your front link design, you could very easily end up with a difference in rotational speed between the front and rear pinions.

As an example, a rear driveshaft with a single cardan joints would cancel out u-joint phases between the pinion speed and the transfercase speed. Couple this to a front double cardon shaft with the pinion operating at a significant angle. The front pinion would be out of phase with the rear; creating bind in the drive train from one end to the other. More stress on the transfercase chain and shafts, more stress on u-joints, axles, tire contact patch, etc. Stress at the tire contact patch would mean less traction available for climbing.

 

[CW]

Point Taken:anon:

 

[XJJPR]

The axle is still traveling thru the "same radius" but not thru the extreme levels of a stock set-up.

If your looking at stock arm location vs Jarm location at the same lift height the axle DOES travel in a different arch.

"its just a drop bracket kit inverted and reversed"

What do you think changing the length of the lower arm in any length or direction (j amr, mid arm or long arm) does?

mark
orgs mfg

 

[Safari Ary]

Mark, I'm not seeing any frameshots on your mounts. I had assumed that you used the stock LCA mounts and made your own upper. Is this correct?? Thanks

Ary

 

[XJJPR]

Mark, I'm not seeing any frameshots on your mounts. I had assumed that you used the stock LCA mounts and made your own upper. Is this correct?? Thanks

Ary

Correct.

The only reason why the upper frame mount is changed is for the 3 link not the j arms.

mark
orgs mfg

 

[Safari Ary]

Correct.

The only reason why the upper frame mount is changed is for the 3 link not the j arms.

mark
orgs mfg

Is it merely strengthened?? Or is it relocated as well? If you could manage to get a pick of that upper frame-side, that would be awesome. You really got me thinking, this could be a lot easier than long arms since i have to do brackets on the axle anyway. There's no way I'm paying 350$ for a bracket kit that takes a couple hours with a plasma, if that, so my bracket options are limitless on the axle end. Thanks

Ary

 

[Paul S]

Can someone (Mark, Richard) clarify the arc/radius of J arms?
It seems to me that they travel in exactly the same radius as short arms, they simply move that travel to an optimum up/down range, as opposed to short arms running in a somewhat back/forward range. If short arms are 16" & J arms are 22", the radius should be about 19" for both. If the above is correct, what you get with J arms is not really a longer arm, but the ability to mount the arms 3 or 4" higher on the axle while maintaining or improving anti dive. If this is true, Richard would see zero difference running J arms, as he has already mounted his arms 3 -4" higher on the axle & also raised his upper arm mount on the axle to maintain good anti dive characteristics.
Paul (I don't need to know how it works, I just copy Richard & Mark) Sinclair