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Old 08-01-2006, 03:43 PM   #1 (permalink)
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3 Link

OK lets beat a dead horse,

I have read and searched, but I am going to ask a question that might seem stupid. What is the right measurements for a front 3 link? I am aware that the link length will change, and the method of mounting will be different for each vehicle, but how about Anti-squat, roll center, and roll axis? I am working on an FJ55 project (http://homepage.mac.com/ryanandjessaka/PhotoAlbum1.html) and some problems with the steering means I am going to have to do a 3 link. I have read the posts and used the 3 link calculator, but am still unsure. I also noticed that the calculator is for rear axles. Will that have any impact on the results?

What I have now:

Wheelbase 107"
Anti-squat 67.34
Roll axis 6.05
Roll center 24.17
8.5" separation at the frame
8.5" separation at the axle

The lower links would be 33" and the upper link would be 35"

Go ahead and tell me to search, but give me some good advise as well.

Thanks,
Ryan

Last edited by scottryana; 08-01-2006 at 05:04 PM.
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Old 08-01-2006, 03:55 PM   #2 (permalink)
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Is that roll center 13" off the ground? Thats pretty low, will result in alot of body sway.
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Old 08-01-2006, 04:04 PM   #3 (permalink)
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jpmassey,

Sorry, I had the wrong info entered for my Panhard bar it should actually be 24.17" with a roll axis angle of 6.05. Any suggestions on what numbers I should be looking for? I have a clean slate to work with, but having never done a 3 link I have no idea, what is ideal and what will kill me.

Thanks,
Ryan.

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Old 08-01-2006, 07:03 PM   #4 (permalink)
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Here's what I'm building right now.



The calculator can be used for front or rear, it's just gonna be anti-dive instead of anti-squat.

Converge the links towards the frame (less seperation there) and I think you'll be happier with it. A good starting point for the frame is to have 75% of the seperation you have at the axle. Mine is 8" and 6" I believe.

Other than that the values don't look too bad. 3-links done this way can have some bitchin clearance issues though. Here's how my crossmember is going together (along with the 4-link rear:

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Old 08-01-2006, 08:07 PM   #5 (permalink)
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How imporant is it to follow the 70% rule? I have been told a couple of times, that I need to make my top link 70% the length of my lower links. I can only think that this would help point the pinion at the TC as the axle drops. Wouldn't this change the caster quite a bit? Maybe the 70% rule is more for rear axles? What do the experts think?

Ryan.
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Old 08-01-2006, 08:46 PM   #6 (permalink)
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I have come up with a 4link for the rear of my YJ how do I put the picture in a post for a critique?

Marc
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Old 08-01-2006, 10:58 PM   #7 (permalink)
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for the front 70%AD is way to much, you want to shoot for no more then 50%AD...IMO 6* roll axis is alittle to steep, even for a steering axle....You also want your upper link to be the same length as or shorter then your lowers......
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Old 08-01-2006, 11:20 PM   #8 (permalink)
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I agree with stomper about the AD being too high

I think the roll axis is in the acceptable range
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Old 08-01-2006, 11:45 PM   #9 (permalink)
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Quote:
Originally Posted by scottryana
How imporant is it to follow the 70% rule? I have been told a couple of times, that I need to make my top link 70% the length of my lower links. I can only think that this would help point the pinion at the TC as the axle drops. Wouldn't this change the caster quite a bit? Maybe the 70% rule is more for rear axles? What do the experts think?

Ryan.
Actually, having the upper link shorter has the opposite effect of what you're describing.

In a nutshell, without inspiring a lot of debate and worthless posts, having the upper link shorter helps keep the anti-dive/squat characteristics favorable throughout the whole range of your suspension.

Keeping them equal length will maintain your same caster angle.

Having the upper length longer will give you a better pinion angle, at the expense of having a good caster angle throughout travel and also at the expense of having any movement from that point of reference.

I know the advantages of making it shorter; however in mine I made the upper link longer because I was going to have issues with the pinion angle. Your situation might be different.
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