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Discussion Starter · #41 · (Edited)

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Discussion Starter · #42 · (Edited)
Hey Larry....
Here's a pic of the home built buggy I was talking about earlier today.









See? Nice home built ones are out there. They're just harder to find. I have a feeling that if you end up building your own, your's will be one of them! :)

Oh, and this guy wants $80K for it! Yikes! Nice, but not that nice.

Sean
 

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Sean thanks again. Hopefully these will help. As you can see that gas tank is real close. And what you're saying about panhard's circular motion does make sense; makes me even more interested in a heavily triangulated 4-link that wouldn't need a one.

Your lengthy theory explanations obviously take quite a lot of effort and I appreciate it greatly.

Do the uppers converge on top of the axle or are they like the 3rd Gen 4Runners' 4 links where the lowers are basically straight, and the uppers coverge but are still over a foot and a half between them on the axle and then the run a panhard to locate from side to side?
The latter:














To answer your question....yes, you can do either a traditional converging upper with straight lower 4 link or dual triangulated 4 link to get rid of the panhard. Problem is.....to do the best one of these (and IMO, the best rear 4link for a TRAIL rig) i.e., the dual triangulated 4 link....you need to SERIOUSLY modify the rear frame....as in cut it off and tube the back end. Unless, you want to try and notch the frame to allow the lowers to travel up into it as the suspension compresses.



Love the XX 4-link idea and I think I can tell from your photos that the uppers would have to come up real high indeed. However I don't see how I need to do anything major on the frame yet.

Very cool idea to get different triangulation from the lower vs. the upper. Now that is ingenious. So far I think that is the s**t. But obviously the lower ends would need a crossmember to meet at, and for sure the gas tank is outta there.

I don't suppose it's possible to point the uppers back behind the axle, pointing backwards....?
 

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Discussion Starter · #44 · (Edited)
The pics you posted help alot. It's pretty much identical to the 4Runner I have.

Are you planning on moving the rear axle back at all? I'd guess no....but figure I should ask. I'm planning to move mine back about 3-4", but not everyone is looking for longer WB. The extra wheelbase may give you the longer links you're looking for to get your LT....but I'd doubt you'll move it back far enough for that alone to work.

After seeing those pics (excellent btw).....I don't see any real reason to run anything other than the 3 link with panhard. It's definitley the easiest thing to do. Just run longer arms in new mounts and beef up the panhard and mount and you should be good to go.

One thing I noticed about MissFJ's rig that is a design constraint of the FJ (unless you move the gas tank) is the fact that the frame captures for the lower links are low hanging under the frame. In the rocks, that will get you caught up from time to time....in your application, it may not matter at all.

If you'd like to experiment with different roll centers, roll axis, instant centers, anti-squat numbers and the like, you can plug your own measurements into that 3 link calculator I linked in post #41.

That way you can optimize where you mount your links for your specific vehicle, the ride height you will be at, the tire size you plan to run, the overall weight, the link material and rod ends you choose, etc.

I'm not sure about the 3 link calculator (haven't used it yet), but the 4 link one will show what the numbers change to not only at ride height but at full bump or full droop. It will even graph the side and plan view of how the links will look.


As for the comment about not seeing that you'll have to do much to the frame to make a XX 4 link work....I'd suggest you get a piece of PVC or wood or whatever about 40-50" long. Put it on the very outside of the driver's side axle tube....towards the wheel and angle it in somewhere just under but to the driver's side of the DS. Now, pretend the axle tube is cycling upwards on compression. How many inches does the axle tube (where this lower link would mount) travel if the front end (underneath but to the side of the DS) is fixed? I think you will find that the 40" long PVC pipe will have to travel into the frame before you can use all of your uptravel.

I don't get the last part. Yes, you can mount your uppers on the back side of the rear axle....but often that leads to some weird pinion rotation.

Also, as a very general guideline you need about 1/4 of the tire's overall height in vertical seperation between upper and lower links. For a 40" tire.....that's 10 inches. Now, that's not usually practical, and you can get by with less....like 8" or so. But just thought I'd throw that out there in case you want to figure how much vertical seperation you need at the axle with whatever size tire you plan to run.

If you can explain the last sentence in another way, maybe I'll understand what you meant better. ***EDIT*** Then again, maybe not....I'm not that bright, especially when it comes to understanding the meaning on a message board. :lol:

Thanks,
Sean
 

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Discussion Starter · #45 ·
Oh, one other very general rule. When building a link suspension....think long and flat.

You want to get your links as long as reasonable (not so long they hang up on everything) and as flat as reasonable. The less angle you have and the longer they are, the more stable your AS (anti squat), RC (Roll center), IC ( Instant Center), RA (Roll Axis) numbers will be throughout the range of travel.

This is just a general rule of thumb. To maximize these numbers while actually fitting them into your vehicle is the hard part. Sometimes you just have to compromise. At that point, you find the best alternative from the compromises available. That's really what the calculators are good for b/c ultimately, you have to put stuff where it fits.

Sean
 

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Are you planning on moving the rear axle back at all?
Nope - haven't really gone there.

After seeing those pics (excellent btw).....I don't see any real reason to run anything other than the 3 link with panhard. It's definitley the easiest thing to do. Just run longer arms in new mounts and beef up the panhard and mount and you should be good to go.
OK so you like Sillyneck's version then? Jason was sort of ho-hum about it but perhaps I misread him. I certainly like simple, and lightweight most importantly.

One thing I noticed about MissFJ's rig that is a design constraint of the FJ (unless you move the gas tank) is the fact that the frame captures for the lower links are low hanging under the frame.
Yes the gas tank location appears to be the only reason for that. It seems like they could have easily gone inside the rails and adapted the tank design to fit.

If you'd like to experiment with different roll centers, roll axis, instant centers, anti-squat numbers and the like, you can plug your own measurements into that 3 link calculator I linked in post #41.

That way you can optimize where you mount your links for your specific vehicle, the ride height you will be at, the tire size you plan to run, the overall weight, the link material and rod ends you choose, etc.

I'm not sure about the 3 link calculator (haven't used it yet), but the 4 link one will show what the numbers change to not only at ride height but at full bump or full droop. It will even graph the side and plan view of how the links will look.
Yeah I'm turning Jason on to that if he isn't doing it already. Great calc.

... you need about 1/4 of the tire's overall height in vertical seperation between upper and lower links. For a 40" tire.....that's 10 inches. Now, that's not usually practical, and you can get by with less....like 8" or so.
34.66" dia. Nitto TG 325/65/18, so 8.6". Thank you for that bit of info.

I don't get the last part. Yes, you can mount your uppers on the back side of the rear axle....but often that leads to some weird pinion rotation. If you can explain the last sentence in another way, maybe I'll understand what you meant better.
I was going out on a limb with an idea that actually wouldn't work now that I think about it. The frame captures for the uppers would be located behind the rear axle, so they would be reversed. This would however let the axle rotate all over the place.
 

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Discussion Starter · #47 ·
Oh, and fitting the 3 link could be pretty simple....get rid of the big flat canister style muffler and go to a smaller, round one or place the muffler farther back (perhaps behind the axle.....depending on your plans for the spare tire).

HTH,
Sean
 

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OK Sean I have hijacked enough on your Bellydoc-worthy thread and you have given me great answers to my questions...thank you again. FYI here is my exhaust (custom URD 3"). I can route it as needed of course.





Here's the Y-pipe which is probably the best-kept secret in FJ mods:



Again, thanks for your help, and indulging me to clutter up your thread.
 

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Discussion Starter · #49 ·
Nope - haven't really gone there.



OK so you like Sillyneck's version then? Jason was sort of ho-hum about it but perhaps I misread him. I certainly like simple, and lightweight most importantly.



Yes the gas tank location appears to be the only reason for that. It seems like they could have easily gone inside the rails and adapted the tank design to fit.



Yeah I'm turning Jason on to that if he isn't doing it already. Great calc.



34.66" dia. Nitto TG 325/65/18, so 8.6". Thank you for that bit of info.



I was going out on a limb with an idea that actually wouldn't work now that I think about it. The frame captures for the uppers would be located behind the rear axle, so they would be reversed. This would however let the axle rotate all over the place.

Hard to say on Sillyneck's version....I haven't really seen it. The only thing I don't like (and won't be doing it like that for this reason) is the low hanging frame captures for the lower links. I'm planning to move my axle back, cut off the existing lower link mounts, french into the frame rails and reinforce them so they are almost flush with the bottom of the frame rails. I'm planning to try and take advantage of the fact that the frame naturally curves up right where the stock lower link mounts are now.

I don't think it would be "easy" for Sillyneck to have designed something else around the stock tank.....hence why I'll be looking for a smaller tank from something like an Isuzu or older 4runner or pickup to put in its place. I'm only doing that b/c the stock tank with skid plate hangs down a full 4" below the frame rails on my 4Runner and I want to get the bottom as smooth as possible. I'm not doing it for the sake of trying to fit a XX 4 link in or even to inboard the lower links on a 3 link. Though....if you're removing your rear spare tire anyway, you may consider relocating a stock tank from something (maybe even the FJC) to that area and mounting it transversely to the frame. That would free up the area in front of the rear axle for whatever link design you could fit....assuming the lower links wouldn't hit the frame rails on compression like I believe they will with the XX 4 link.


I'm 100% positive that Jason knows about the link calculators, but it can't hurt to tell him again. ;)

For roughly a 35" tire, 8.6" is probably perfect....but as I said, you can get by with less. I'd say 6" would be the minimum you'd want to use. Depending on how high up on the axle tube your lowers are mounted that distance should increase to deal with the rotational forces you'll encounter from moving above the axle tube centerline.

I now get what you're saying about mounting the links coming from the back. So they'd mount somewhere back where the spare tire is now and come forward on top of the axle....if I get what you are saying. There was a guy that did that in Tucson on a Jeep. One of the first ones to run Highway to Hell all the way through. The difference in his idea and your's was that all the links came from behind the rear axle, not just the uppers. Then he ran 1/4 elliptical springs from in front of the rear axle back to it. He ended up bending up all kinds of links when dropping off of big rocks and steep ledges. Didn't work very well in the long run. As you already noted though, it wouldn't work the way you described it.

HTH,
Sean
 

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A wealth of information here and a very impressive write-up.
Thanks Sean!!
While I don't plan on going too crazy with my FJ, i like learning about the different set ups out there.
I had an '85 4Runner for the last 12 years that I had a lot of fun with and always wanted to really build it for rock crawling, but instead I got married, had a child and bought an FJ.
Last I heard my old rig was sent to Marlin in northern california to become a real rock crawler/trailer queen.:cowsmile:
 

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Discussion Starter · #51 ·
OK Sean I have hijacked enough on your Bellydoc-worthy thread and you have given me great answers to my questions...thank you again. FYI here is my exhaust (custom URD 3"). I can route it as needed of course.



Again, thanks for your help, and indulging me to clutter up your thread.


Looking at the pics, I'd say it shouldn't be too hard to just move your current exhaust over towards the frame rail a bit and mount your 3rd upper link between it and the driveshaft. Definitely the hardest thing about mounting it would be where to attach it. You *could* add in a heavy crossmember, or possibly beef up the existing stock ones....though major disassembly will be required to basically plate and reinforce (perhaps even add some tubing to triangulate) the stock X-member. I'd think the X member in this pic would be a prime candidate...but dropping the gas tank would be required.




This ain't clutter. :) It's exactly what the thread is for.

Sean
 

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Discussion Starter · #52 ·
A wealth of information here and a very impressive write-up.
Thanks Sean!!
While I don't plan on going too crazy with my FJ, i like learning about the different set ups out there.
I had an '85 4Runner for the last 12 years that I had a lot of fun with and always wanted to really build it for rock crawling, but instead I got married, had a child and bought an FJ.
Last I heard my old rig was sent to Marlin in northern california to become a real rock crawler/trailer queen.:cowsmile:

Thanks very much. I appreciate all the thank yous. Glad to know it's appreciated. I'm having a lot of fun writing this stuff out.....to the detriment of my honey-do's and stuff I need to get done for the Moab trip. It's so dang hot outside I'd rather just sit in here and web wheel rather than get out in the garage and do what needs doing. :lol:

Sean
 

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Discussion Starter · #54 ·
Exactly....but it's hard to tell from a pic. You may get under your truck and go, "there's no way I can fit this in here" or "that crossmember is never going to work....that Sean K. guy is a dumbass". :lol:



That's where I'd start. Doesn't mean it'll work, but it's a starting point. If it won't work, look into making a new crossmember elsewhere, coming off of the frame rail with a supported and boxed capture (while still clearing the exhaust....(tricky)), or going to the crossmember pictured in your bottom most photo of post # 48 (after plating and reinforcing it, of course).

HTH,
Sean
 

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Discussion Starter · #55 ·
One other thing I should mention about a 3 link with a panhard. My admittedly limited understanding is that there is a way to angle your upper link to minimize what's called torque steer. I haven't yet researched this enough to find out exactly how to do it, or what it entails since I haven't gotten anywhere near that point on my 4Runner.

Perhaps Jason will be able to elaborate on the topic....but from what I have seen, a straight link setup like the one you photochopped will work quite effectively...it just places all location of the axle on the panhard so you have to make it strong enough to be up to the task.

I'm the sorta guy that likes to optimize stuff though, so before tackling the 3 link, I want to research a little more to find out the particulars of how to mount the upper to correct for torque steer. When/if I find more info....I'll post up.

Sean
 

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One way to solve this is to lose the tank and get a cell but I am getting cheap now. This is what the DR Baja truck does.
The more I think about it, for long term, this is going to be one of the best decisions I made. I can go for redoing the rear suspension no if I choose and not have to worry about the gas tank, as I can just plump in the fuel cell as a replacement, with the added knowledge that it is safer both on and off road than the factory tank. And a tank, while certainly not in the 99$ range of mods, is still ~$1k or so for 32 gallons, and especially for you with the redone filler door and neck, would be very easy to plumb into an in cab fuel cell.

- SK
 

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Sean-

We spoke on the phone about differentials and I think it would be instructive to have your comments on this thread. And while on the subject of the power train, perhaps transmissions do's/don'ts.
 

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Ok so you must mean this. Sounds terrific - real simple and effective.

Todd is there room to run the upper link over the drive shaft?
like this but on top of it. You have that cross brace to use as the front attachment point and then you just need to weld a mount on top of the pumpkin.
 

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Discussion Starter · #60 ·
You don't want to put it up that high.....again...go back to the basics....links should be long and flat.

What I'd recommend instead is a mount that drops down off a heavily reinforced stock crossmember to remove several inches of angle.

Sean
 
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