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Old 03-23-2017, 06:16 AM   #1 (permalink)
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Need Help Identifying Handling Quirk After 3 Link

I have a '95 4Runner with 3.4 swap on 37"s, low COG build with about 3" of lift. This was my first 3 link but spent years researching and months designing. On paper I believe it to be about as good as it can get given the restraints of the body and frame. I have a little bit of bump steer do to the shorter length of my panhard, but I do not believe that to be my issue.

The rig rides fine down rough roads with potholes and such, and corners very predictably. The issue appears when the road appears relatively smooth but there is a rise or fall in the suspension on just one side from small road surface variations, this causes the rig to want to dart around. I want to label this as roll-axis oversteer but the calculator tells me I have very minimal roll-axis oversteer. I have triple checked all my calculations and everything is correct. I have had the rig checked out at an alignment shop and the toe, caster, etc. is all within spec. I've put about 200 miles on it and everything is tight so this is not a loose link, joint, etc.

Below is the specs on the build. Please give me your input.

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Old 03-23-2017, 06:30 AM   #2 (permalink)
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Show some pictures of the set-up!!
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Old 03-23-2017, 07:02 AM   #3 (permalink)
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You have either to much or to little toe in your alignment.

And pictures would help too.
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Old 03-23-2017, 07:36 AM   #4 (permalink)
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I'll get some pics shortly. It initially felt like toe to me as well, but I measured it at 1/8" of toe in. Even had an alignment shop confirm it. I changed it by 1/8" in both directions and it didn't seem to make a difference.

Also, forgot to mention that I am running the chevy 63"s in the rear.
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Old 03-23-2017, 07:40 AM   #5 (permalink)
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Hard to tell from the cropped picture, but I'd guess you have a lot of bump steer from your angled links.

As the panhard comes up, axle shifts side ways, one link gets longer, other gets shorter, axle steers. With your upper link setup you may also be changing caster at the same time.

Hard to say though without pics.
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Old 03-23-2017, 07:56 AM   #6 (permalink)
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4WU, I wanted to go with your kit but ended up chopping down a Chevy D44 so half of the brackets wouldn't work and the upper is on the wrong side for what I wanted to do. You guys make some awesome stuff!





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Old 03-23-2017, 11:53 AM   #7 (permalink)
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Is the picture deceiving or is your tie rod substantially longer than your drag link.
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Old 03-23-2017, 12:23 PM   #8 (permalink)
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Is the picture deceiving or is your tie rod substantially longer than your drag link.


Do you mean longer than the pan-hard bar?
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Old 03-23-2017, 12:40 PM   #9 (permalink)
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Whoops, yeah that's what I meant.

Drag link vs panhard.
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Old 03-23-2017, 01:09 PM   #10 (permalink)
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Whoops, yeah that's what I meant.

Drag link vs panhard.



That's the only out of whack thing I'm seeing.
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Old 03-23-2017, 01:31 PM   #11 (permalink)
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My rig is very low and I just can't see how to reduce the angle of the lower links without losing tons of ground clearance. I've ridden in several rigs with worse lower link angles that don't exhibit this issue.

The only thing I kept coming back to was the panhard length. I was trying to keep it short to maximize up travel because it is the first thing to hit the frame if I had it longer. My previous rig was radius armed and had a similar length relationship between the panhard and drag but that suspension has a lot more inherent bind and restriction. I was having trouble wrapping my head around how that was causing the issue but like usual I should do less thinking and more fabbing. Thanks for the advice.

Whenever I get the time to redo the panhard bar I will reply with my findings.
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Old 03-23-2017, 02:17 PM   #12 (permalink)
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Originally Posted by jpalmer View Post
My rig is very low and I just can't see how to reduce the angle of the lower links without losing tons of ground clearance. I've ridden in several rigs with worse lower link angles that don't exhibit this issue.

The only thing I kept coming back to was the panhard length. I was trying to keep it short to maximize up travel because it is the first thing to hit the frame if I had it longer. My previous rig was radius armed and had a similar length relationship between the panhard and drag but that suspension has a lot more inherent bind and restriction. I was having trouble wrapping my head around how that was causing the issue but like usual I should do less thinking and more fabbing. Thanks for the advice.

Whenever I get the time to redo the panhard bar I will reply with my findings.



What if ( and I know it may not be legal) you moved the tie rod back to match the panhard
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Old 03-23-2017, 02:20 PM   #13 (permalink)
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You could build and install a new tie rod for around a hundred dollars



Use a heim and a couple of tabs for the draglink side
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Old 03-23-2017, 02:31 PM   #14 (permalink)
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I think you caster is the culprit. The upper control link is longer than the lower link. When you check the caster at ride height, it is correct, but when the suspension cycles up or down, the longer link will rotate the axle forward, throwing the caster out. Try adding 3-4 degrees of caster(Rotate the axle back), see if that helps, of course it may cause your u-joints to bind at full droop, but that's another problem!
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Old 03-23-2017, 02:42 PM   #15 (permalink)
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Are you using ballistic joints? Looks like them. If they are did you tighten the shit out of the lockrings? They dont come ready to run and tight how you'd expect. My buddy got some recently and if we had just slapped them in and took off it would have been slopy as hell. If theyre not the ballistic joints disregard all that.

Id notch the frame and build both new mounts to get the panhard as close to the drag link as possible. Its silly to put as much work as you have to skimp on this.
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Old 03-23-2017, 05:13 PM   #16 (permalink)
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Your Panhard needs to be on the same plane as the tierod!! Fought the same problem on a Dodge van that we did a SAS on years ago, changed the panhard to be on the same plane as the TR, problem went away!!
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Old 03-24-2017, 04:13 PM   #17 (permalink)
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What are you running for rear suspension? If it is stock link setup and lifted your problem could be back there. I have not looked that closely at the 2nd gen 4 runner but it is similar to the 3rd gen and those have a pretty horrible roll axis and really bad roll steer. When you lift them it only gets worse. Your softer front suspension might be allowing the truck to body roll more which would make you feel the crappy rear suspension more.

Your front roll axis is a little bit positive but there is only so much you can do with a three link, though flatter links would help.

I am less concerned about your DL and PH being different lengths than I am about them being different angles. With different lengths the angle relationship will change a little through travel so it is even more critical that they start out the same angle at ride height. That being said I doubt that is your problem because it sounds like this is happening with very minimal front suspension movement and problems there would tend to be felt at the extremes of your up/down travel.

Your panhard is a little on the steep side which may not be helping things. Starting out flatter gives you less sideways axle movement. Some of what you are feeling may even be the body shifting sideways as the suspension compresses
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Old 04-06-2017, 08:50 AM   #18 (permalink)
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Sorry I went dark, life got the best of me for a while. I appreciate all the advice and input. I will try and answer all of your questions and update what I have tried since I last posted.

I fabbed a new panhard mount and increased the drag link length 6Ē. The axle side is now in exactly the same place as the drag link and the frame side is only about 1.5Ē shy of the draglink. The angle is now perfect at ride height as well. Sadly, this made little to no discernable difference. Just feels like something is loose but I canít find anything.



Regarding the caster, I had it at +7 and dialed it back to +4 to see if this made a difference and it did not. I figured with a long upper link it would reduce the amount the angle changed as the axle cycled? That was my thought process when I built it anyway. We are only talking a couple inches of suspension travel that causes the issue, canít see it changing the angle enough to make it feel sketchy but I could be wrong.

I am using Ballistic Joints. I checked them but did not tighten the piss out of them. Iíll take a link out tonight and see how much I can crank them down. This would go along with my gut that something feels loose.

I am running the garden variety Chevy 63Ē springs on the back.

After driving it some more I will try and describe the problem better. When the axle compresses evenly everything is good. When one side compresses the vehicle steers away from that side. Passenger side compresses and the rig steers driver, driver compresses and the rig steers passenger. That describes bump steer, but the steering wheel does not move during this process.
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Old 04-06-2017, 03:58 PM   #19 (permalink)
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Have you considered removing the coil springs and flexing the axle with a jack while observing the change in steering angle?
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Old 04-06-2017, 04:01 PM   #20 (permalink)
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I have not. Honestly I don't know if I would know what a normal amount of change would be to the steering geometry, caster, etc.
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Old 04-06-2017, 05:53 PM   #21 (permalink)
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Quote:
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I fabbed a new panhard mount and increased the drag link length 6”. .
I am telling your Panhard needs to be on the same plane as the tierod not the draglink. I went through the same BS years ago and as soon as we made the PB on the same plane as the tierod, the problem was gone. Two hundred thousand I give a shit if you do not want to listen to me!!
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Old 04-06-2017, 06:26 PM   #22 (permalink)
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That is just so opposite of what I have always done and been taught but I won't discount your experience. My steering geometry is pretty much perfect in my book but apparently my book is missing some pages because I have problems. I'll try and mock something up to survive a road test and see if that helps.
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Old 04-06-2017, 07:14 PM   #23 (permalink)
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I have not. Honestly I don't know if I would know what a normal amount of change would be to the steering geometry, caster, etc.
My suggestion is less about comparison than to establish what you have.
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Old 04-06-2017, 07:16 PM   #24 (permalink)
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I am telling your Panhard needs to be on the same plane as the tierod not the draglink. I went through the same BS years ago and as soon as we made the PB on the same plane as the tierod, the problem was gone. Two hundred thousand I give a shit if you do not want to listen to me!!
X2! If it's not on the same plane as the tie rod the axle will shift towards passenger on up travel and drivers on down. Pan hard parallel with the tie rod/axle will minimize the shift. It dosnt take much of a shift to make a vehicle dart around after a shift especially at normal road driving speeds!
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Old 04-06-2017, 10:40 PM   #25 (permalink)
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I am telling your Panhard needs to be on the same plane as the tierod not the draglink. I went through the same BS years ago and as soon as we made the PB on the same plane as the tierod, the problem was gone. Two hundred thousand I give a shit if you do not want to listen to me!!
I believe that you felt an improvement but I think it was from the fact that the panhard was flatter. I think to say "parallel to the tie rod" just confused people. If the drag link is not also flat you would get bump steer but in some circumstances I could see the benefits of choosing a flatter panhard over zero bump steer.

I ran a double triangulated 4 link in my buggy with crossover steering and a fairly steep drag link for years and never really felt any bump steer. It was not a good idea and had lots of other downsides but bump steer was not one of them, even though "by the book" it should have had lots of it. That setup would have acted very similar to a three link with a flat panhard and steep drag link.

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