Front and Rear Track Bar Question

ABadJeeper

ABadJeeper

Carolina Metal Masters
Joined
Jan 7, 2007
Location
Huntersville, NC
So some of you may have seen my other thread where I'm having problems with my 14 Bolt in the back of my JK hitting the gas tank when I stuff the right rear.

I've been thinking about a number of solutions from a Dana 80 with a centered pinion to moving the gas tank to behind the axle. Most of these solutions require a fair bit of money and I already feel like I should just stop putting money into this thing and build or buy a buggy.

Well last night after I mowed my lawn I was looking at a rear brake issue I'm having and thought what about swapping the track bar around so the axle side is on the passenger side. This would pull the axle away from the gas tank. My only concern is what this is going to do to the drivability of the Jeep since now both the front and rear track bars are swinging in the same arc as opposed to against one another.

I've never seen a setup like this and I can't seem to find any information that says it won't work. I think at low speeds things would be fine but it's the road handling that I'm the most worried about. I still like to drive the Jeep when it's nice and I'm wondering if having both track bars swinging in the same plan would make things twitchy over bumps and whatnot. What do you guys think.
 
Having the 8 inch bracket roughly means that the drivers side of the axle is mostly pivoting at a point 8 inches above axle centerline when the right rear is compressing. That's slightly oversimplifying it. When the tire that is opposite to the axle end of the track bar (the right rear in this case) moves vertically, the left wheel and the differential both move vertically significantly more than if the track bar pivot was at axle centerline.

Basically, for the same amount of RR wheel travel, a track bar pivot at a lower height would move the differential less. It will also lower the roll center, which is usually a good thing. Generally speaking, having the track bar level is usually the most important thing, but you've discovered one of the other important things. In this case, that important thing usually doesn't matter very much if you're going slow when offroad, until you find out it's also creating a clearance problem because of the extra motion.

So making the axle side bracket shorter, and making the chassis side longer to match should give you more diff-to-tank clearance with no other changes. Well, you might need a different track bar with a curve or jog in it to clear the diff or something like that. No idea what clearance would be like.

Keep the bar level, just change its vertical height from axle centerline. Fix the problem, don't just move the problem to the other side of the vehicle.
 
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Whoa, an actual picture to illustrate this! That's actually pretty rare. Courtesy of Toyota 4Runner Forum - Largest 4Runner Forum via Google.

So visualize the axle with the longer bracket, but make it rotate the opposite direction (opposite wheel up instead of down). See how much the diff moves for the same amount of axle angle?

Again, this is slightly oversimplifying the motion path of the axle and trackbar.

awww.toyota_4runner.org_attachments_5th_gen_t4rs_168092d14388755d08886db3a1afd7261c73e8ce72149.jpg
 
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Fabrik8 - You have done a great job explaining this and the picture only makes it that much better

Edit* You've explained very well how just changing the track bar in relation to the axle will help fix this particular issue but I'm now curious about the OP question. Will having both front and rear track bars mounted in the same direction(both frame side mounts being on the driver side for example) cause any ill effects?
 
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adamk said:
Will having both front and rear track bars mounted in the same direction(both frame side mounts being on the driver side for example) cause any ill effects?
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I've been really pondering that one. There's probably an easy answer, but I don't know what it is because I mostly deal with vehicles that don't have a solid axle in the front. My intuition is that you'd want to keep them opposite directions, to help cancel any asymmetric affects from axle lateral motion during axle travel. Even if you start out with level track bars, as soon as you go over a bump or dip in the road, you have non-level track bars, and then you have combined vertical and lateral forces that are greater in one direction than the other. If you have those asymmetrical forces on both ends at once and going the same direction, you could potentially have very different vehicle behavior around left turns than around right turns, etc.

Still working on that one in my head. Track bar layout is all about making the best out of a not-so-great concept though, so it's really just about minimizing the bad parts because they're simple and light and cheap.

It's the same arguments about compromise that you can make about solid axles too. ;)
 
Fabrik8 said:
you could potentially have very different vehicle behavior around left turns than around right turns, etc.
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This is exactly what I was thinking. Since the track bar isn't truely level from the factory, if you hit a dip in the road and both front and rear suspension compress, it would want to push the body of the vehicle to one side. Same goes for in a corner. With them opposite and in the same situation, it would want the frame to "twist"
 
paradisePWoffrd said:
what about the front panhard?
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Front track bar is mounted on the frame and the geometry is as close as it gets working with my steering. I'm gonna guess it's on a 5-10* angle. Not flat but way closer than stock. IIRC my front track bar is 6" over centerline on the axle.

Fabrik8 As far as the roll centers go on a lifted vehicle you actually want the roll center raised to help with handling and off camber stuff.

After looking at it again and thinking about it more I'm 60/40 for travel and I think if I lower the chassis side bracket 2" it will help because then it won't swing as much. I'm not sure if it's enough to actually make a difference or not though. I have a new chassis side bracket floating around somewhere I can try. I think I've nixed switching sides.
 
jeepinmatt said:
You need a Watts link front and rear. Won't really help with packaging, but top notch for handling.
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From my understanding if he's still using a steering box up front he had to use a track bar or deal with bump steer very bad, same reason you can run a single or double triangulated 4 link up front without a track bar.
 
adamk said:
This is exactly what I was thinking. Since the track bar isn't truely level from the factory, if you hit a dip in the road and both front and rear suspension compress, it would want to push the body of the vehicle to one side. Same goes for in a corner. With them opposite and in the same situation, it would want the frame to "twist"
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When you turned one direction you'd have massive amounts of body roll, and the other direction you would barely have any if I'm wrapping my brain around it correctly.
 
iwaxmyjimmy said:
When you turned one direction you'd have massive amounts of body roll, and the other direction you would barely have any if I'm wrapping my brain around it correctly.
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The amount would depend on a few factors, like the distance from the roll center to the CG and things like that. Roll isn't really that asymmetric with good track bar geometry.
 
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jeepinmatt said:
You need a Watts link front and rear. Won't really help with packaging, but top notch for handling.
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That would be a packaging nightmare. LOL The front I'd have to run 10" of lift and in the rear it would be doable if I wasn't running a 3-link. I think Full Traction actually makes a kit for the JK but that is with stock axles and whatnot.
 
Fabrik8 said:
The amount would depend on a few factors, like the distance from the roll center to the CG and things like that. Roll isn't really that asymmetric with good track bar geometry.
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X2. The suspension would also want to roll around the RC of each end, and you cant assume that is the center of the vehicle. Also factoring in properly tuned shocks and sway bars, you could likely control the movement extremely well.

I tried finding with no luck, but there is a thread on pirate where some of the ULTRA4 guys discuss running 3 link F&R. IIRC some of them indicated they preferred both panhards in the same direction because it was more predictable, even though it wasn't technically as good. Ill try to find it again.
 
paradisePWoffrd said:
I tried finding with no luck, but there is a thread on pirate where some of the ULTRA4 guys discuss running 3 link F&R. IIRC some of them indicated they preferred both panhards in the same direction because it was more predictable, even though it wasn't technically as good. Ill try to find it again.
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Off road, I can't see any problems because everything is so slow. At road speeds though, panhards in the same direction may get a little sketchy for predictable handling.
 
Fabrik8 said:
Off road, I can't see any problems because everything is so slow. At road speeds though, panhards in the same direction may get a little sketchy for predictable handling.
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The Ultra4 guys I was referring to aren't going slow... A few races some of them see 100+ mph in the desert. I could be remembering incorrectly. Ill try to find the discussion.
 
paradisePWoffrd said:
X2. The suspension would also want to roll around the RC of each end, and you cant assume that is the center of the vehicle. Also factoring in properly tuned shocks and sway bars, you could likely control the movement extremely well.

I tried finding with no luck, but there is a thread on pirate where some of the ULTRA4 guys discuss running 3 link F&R. IIRC some of them indicated they preferred both panhards in the same direction because it was more predictable, even though it wasn't technically as good. Ill try to find it again.
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Fabrik8 said:
Sweet, I'd love to know an answer about that to satisfy my curiosity.
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I'm off to search Pirate. I really want to know the answer too.
 
ABadJeeper said:
Fabrik8 As far as the roll centers go on a lifted vehicle you actually want the roll center raised to help with handling and off camber stuff.
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Missed this earlier. There are a number of arguments out there about RC height. I would agree for more trail rigs and low speed having the RC higher, but at speed it gives you a false sense of security, and no warning that you are going to roll before it happens.


Fabrik8 said:
Sweet, I'd love to know an answer about that to satisfy my curiosity.
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I know, it has me curious as well. I would personally keep them opposing one another, and lower the panhard closer to the axle centerline..
 
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