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Unread 10-18-2012, 04:04 PM   #61
cycleguy04
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I have just one more question before I'm sold on the idea of a mid arm setup.

What are the disadvantages of a good longarm kit and why would I choose to do the custom mid arm suspension over a one?

Obviously one reason is clearance. If I could buy a four link long arm kit with the lower brackets integrated into a flat belly skid, that would save me a lot of time, of which I do not have. Less time in the garage the wife stays happier. Happy wife, happy...

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Unread 10-18-2012, 06:58 PM   #62
Imped
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Clearance.

You just don't need arms that long.
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Unread 10-18-2012, 07:14 PM   #63
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Quote:
Originally Posted by cycleguy04
Less time in the garage the wife stays happier. Happy wife, happy...
I can categorically state that I have already told you how to fix that kind of issue...

Also, I'm seconding the "clearance" argument and furthermore referring you back to the part of the four-link rear where BOTH ends of your links get relocated. A lot of bolt-on kits don't address the axle end, and some leave the track bar in place, as well.
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Unread 10-18-2012, 07:20 PM   #64
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Quote:
Originally Posted by Sundowner

I can categorically state that I have already told you how to fix that kind of issue...

Also, I'm seconding the "clearance" argument and furthermore referring you back to the part of the four-link rear where BOTH ends of your links get relocated. A lot of bolt-on kits don't address the axle end, and some leave the track bar in place, as well.
Sold. Now to address that time issue and finish the other projects I've stacked up, then I can start making measurements and playing with the calculator.
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Unread 10-19-2012, 06:53 AM   #65
RubiconRazorbac
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Quote:
Originally Posted by cycleguy04 View Post
Sold. Now to address that time issue and finish the other projects I've stacked up, then I can start making measurements and playing with the calculator.
Take your time. It adds up and one thing leads to another. Then you change your mind. Ask me how I know
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Your shaft isn't long enough to handle that kind of droop...
My build thread: http://www.jeepforum.com/forum/f9/ru...thread-792423/
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Unread 10-22-2012, 08:49 AM   #66
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Thank you again to all who have replied. I am sure that all the info in this thread will give anybody confidence when designing a rear suspension. I also think the truss discussion has been helpful. All of this leaves me wanting more info though, so is there any way we move the discussion to the front suspension?

I know enough to know that the 3-link front with trackbar is the way that most people go, but what is truly needed to get that done?

Also, is there a calculator for the front end similar to the 4 link calc from Pirate? If so, what do the terms mean and what are we looking for?

Thanks in advance.

Lee
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Unread 10-22-2012, 09:05 AM   #67
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Yes, a Pirate 3 link calc exactly like the 4 link calc exists. Just like the 4 link calc, my recommendation would be don't read too far into it.......I didn't even touch the 3 link calc until after it was done. Just view the front just like you view the rear. The rear squats under acceleration and the front squats under braking (weight transfer instances)....called anti-dive. For the most part, you set the front and rear suspensions up similarly. My front and rear suspensions are nearly mirror images of each other, aside from some horizontal separation differences in my front upper link. The lower link mounts and link lengths are mirrored.





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Unread 10-22-2012, 09:30 AM   #68
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Thanks Connor. I guess the front scares me a little bit because there is so much more going on up there. The rear really seems simple in comparison as you aren't working around the steering, trackbar, etc. It would seem that the way to go about it would be to remove the passenger upper. Is there any additional triangulation that needs to be done because of removing the link? I assume not since the trackbar is still locating the axle. I would also assume that trussing the front would be necessary at that point since the remaining upper link would now see a lot more stress?

When you say the lower link mounts are mirrored, you literally mean you used the exact same mount correct? If memory serves from your build thread, you didn't use the one piece lower/upper mounts correct? Approximately what is the angle needed for the upper mount? I ask because I would guess the front is a different angle than the 25 degree rear upper and I'd like to figure out whether there is a premade lower/upper similar to that which people use in the rear.
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Unread 10-22-2012, 09:51 AM   #69
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Quote:
Originally Posted by srfnfly227
Is there any additional triangulation that needs to be done because of removing the link? I assume not since the trackbar is still locating the axle. I would also assume that trussing the front would be necessary at that point since the remaining upper link would now see a lot more stress?
I'm curious about this as well. If I were to keep the upper axle mount as far away from the lower radiator neck as possible, how will that affect the geometry?
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Unread 10-22-2012, 11:59 AM   #70
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Quote:
Originally Posted by srfnfly227 View Post
Thanks Connor. I guess the front scares me a little bit because there is so much more going on up there. The rear really seems simple in comparison as you aren't working around the steering, trackbar, etc.
True. Just remove that stuff from the equation. It only enters it when it comes to clearance at full bump. Set the axle as far forward as it can go and at full bump and build the suspension at that point.....then you won't run into any surprises later on. Once it's tacked up, cycle and go from there.
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Originally Posted by srfnfly227 View Post
It would seem that the way to go about it would be to remove the passenger upper. Is there any additional triangulation that needs to be done because of removing the link? I assume not since the trackbar is still locating the axle. I would also assume that trussing the front would be necessary at that point since the remaining upper link would now see a lot more stress?
That's generally the easiest way under a TJ. The track bar is still taking care of keeping the axle in place laterally. The upper arm is preventing the pinion from rolling down when under compression and preventing it from rolling up when under tension. Look at my picture...you do not want to use the factory mount--cut it off, smooth it out and forget about it. A small 2" joint won't last long when taking the full load of those forces. I used some 1/2" steel for a simple bridge/truss for the upper link. The arm is made from 2" x .25" wall DOM and I use the big 1.25" shank 2.5" JJ's at both ends. The frame mount and axle link tabs are 3/8" steel. Steel thickness for the arm and mounts is overkill but it's what I had available and going over-beef when relying on one arm never hurt anyone.
Quote:
Originally Posted by srfnfly227 View Post
When you say the lower link mounts are mirrored, you literally mean you used the exact same mount correct? If memory serves from your build thread, you didn't use the one piece lower/upper mounts correct?
Same mounts, yes. All 4 are from Poly. I built the front upper link mount.
Quote:
Originally Posted by srfnfly227 View Post
Approximately what is the angle needed for the upper mount? I ask because I would guess the front is a different angle than the 25 degree rear upper and I'd like to figure out whether there is a premade lower/upper similar to that which people use in the rear.
There is no required angle. I simply built the outside portion of the frame mount and tacked the truss in place, bolted up a JJ, slid some tube over the tube adapter and swung it down to the axle. With the JJ centered, I oriented the mount to put the other end of the tube where I wanted it on the truss....pretty much centered over the top of the diff. I tacked the frame mount to keep it in place, built the arm, and tacked up the axle tabs. I cycled the axle to make sure nothing hit and burned it all in.
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Originally Posted by MisfitSeven View Post
I'm curious about this as well. If I were to keep the upper axle mount as far away from the lower radiator neck as possible, how will that affect the geometry?
I'm trying to remember where my joint is relative to the radiator neck but at full bump, I made sure there was a safe amount of clearance. The angle of the arm is very inelastic when it comes to the calc outputs. Just follow the convention I did and worry more about it clearing everything.

Disclaimer:
Keep in mine my Jeep hasn't moved since completing the front suspension several months ago and this is my first 3 link. But I've got every reason to believe it'll perform just as I'm expecting it to.
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Unread 10-27-2012, 05:30 AM   #71
Motas
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Hey guys. Does anyone have a good diagram showing how the roll axis is figured out? After a few hours of reading I finally got anti squat and anti dive worked out and why it changes but cant get my head around what changes the roll axis. Also in the calculator what sort of figures should I be aiming for for the roll axis? I realize I am not aiming for a specific number because my situation is different. But for example 100% anti squat means no squat or dive, what do the numbers for roll mean in real life? After much research I think I am aiming for 105-110% anti squat, a low roll axis tilted slightly down at the front. From this I am hoping to get good handling characteristics on the street (roll axis leaning forward), good absorbing bumps at high speed (low roll axis), good handling at higher speeds (anti rock to limit sway caused by low roll axis), and stability on steep climbs (slightly over 100% anti squat). Is this a good aim? Our terrain over here is mostly muddy rutted hill climbs which is done with momentum so im generally higher speed than you guys and also want it to drive good in the desert for "prerunning". So it needs to soak up bumps and things well but also needs to be stable. Luckily I do not need heaps of flex so can run the sway bars.
Any advice is much appreciated.
Thanks.
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Unread 10-27-2012, 06:14 AM   #72
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Quote:
Originally Posted by Motas
Hey guys. Does anyone have a good diagram showing how the roll axis is figured out? After a few hours of reading I finally got anti squat and anti dive worked out and why it changes but cant get my head around what changes the roll axis. Also in the calculator what sort of figures should I be aiming for for the roll axis? I realize I am not aiming for a specific number because my situation is different. But for example 100% anti squat means no squat or dive, what do the numbers for roll mean in real life? After much research I think I am aiming for 105-110% anti squat, a low roll axis tilted slightly down at the front. From this I am hoping to get good handling characteristics on the street (roll axis leaning forward), good absorbing bumps at high speed (low roll axis), good handling at higher speeds (anti rock to limit sway caused by low roll axis), and stability on steep climbs (slightly over 100% anti squat). Is this a good aim? Our terrain over here is mostly muddy rutted hill climbs which is done with momentum so im generally higher speed than you guys and also want it to drive good in the desert for "prerunning". So it needs to soak up bumps and things well but also needs to be stable. Luckily I do not need heaps of flex so can run the sway bars.
Any advice is much appreciated.
Thanks.
The link calculator should make the roll axis pretty clear, if I'm remembering it correctly...

I'm glad that you recognize sway bars as good things, and flexibility as a poor second by comparison. That's not to say that they're mutually exclusive, mind you... just that you want them much more than you don't want them.
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Unread 10-27-2012, 03:15 PM   #73
Motas
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It shows the axis clearly but doesn't show how it gets it. I find it helps to know how to get the axis so I know how to adjust it properly. Just haven't been able to get my head around it from the explanations I've found.
Thanks.
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Unread 10-28-2012, 11:49 AM   #74
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If I remember correctly the roll axis angle can be changed by raising or lowering the track bar mounts in the front or raising the upper mounts in the rear on the axle. Also if you make a double triagulated 4 link it changes the roll axis angle. I ran calculations and got everything as close as I could and ran it. With a stock rear sway bar and a Anti rock on the 2nd hole to the rear my Jeep drives great. My jeep off road does not hop and really doesnt squat It climbs well and is very predictable.
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Unread 10-29-2012, 02:33 AM   #75
9703tj
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Subscribing because I don't NEED long arms...

But I'm going to run them anyways...

I don't NEED wonton full width axles..

I don't NEED hydro steering...

I don't NEED a bigger engine...

I don't NEED steeper gears in my T-case....

But I'm gonna run all of that anyways...

Geometry wise: Well set up long arms travel in less of an arc than short arms, or mid arms do, thus causing less unwanted steering input due to suspension flex. Piss poor set up long arms can cause all sorts of other problems, unwanted steering input being the least of them...
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