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Rear Links - And so it begins - finally!

Discussion in 'Center Of Gravity' started by BadDog, Feb 9, 2005.

  1. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    So I'm finally getting started. Check it out and let me know what you think. Also look at the "4 link calculator" and let me know what you think about the values...

    Progress page

    DONE! Final Update 3/10/05
     
    Last edited: Mar 10, 2005
  2. sled_dog

    sled_dog 1 ton status

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    finally. Your upper links are going to be how far from the axle tubes up?
     
  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    The "z" values refer to the height of the links.....it looks like the axle-end links are 12" apart from each other, and the frame end ones are about 4" apart.
     
  4. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    That is correct. It's the best arrangement I could come up with and still fit around everything. Exhaust and drive shaft caused major problems. If my wheel base were a bit shorter, or the drive train pushed back about 8-12", it would have been much better, but the exhaust would still be a problem.
     
  5. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Russ,


    Try flipping your headers over.... not only will it give you WAY better clearance, but it will keep your face warm while you're wheeling !!!

    Buwahahaaaaaaaa
     
  6. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Headers? I aint running no stinking headers! ;)
     
  7. PJTPW

    PJTPW 1/2 ton status

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    Any plans to mount the lowers above the axle centerline?

    That would be my only suggestion. It would definately help with A.S.

    Ryan
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Yeah, I thought about that, but it sure does increase stress on the lower links. The rod ends can handle it, but I worry what will happen if it's under heavy compression and gets bumped. :eek: But it sure will help the numbers won't it... :D I may put it in as an adjustment point anyway...
     
  9. PJTPW

    PJTPW 1/2 ton status

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    I would do it. Just build the lowers out of 2 x .25 wall.

    I really don't understand why so many people build the lowers out of 1.75 x .375 wall. It's heavier, and less bend resistant than the 2 x .25 wall.

    My .02

    Ryan
     
  10. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Already planning on 2 x 0.250, but it still dents and collapses if it is tweaked under stress. It won't smooth bend as easily as 1.75 x 0.375, but according to my understanding, the thinner wall can still "dent" easier with a point load. I can just see throttle down on a near vertical line, a little bounce and grab, just as a link hits the ledge, and taco city. Believe me, if it CAN happen, it WILL happen to me.

    That's why I'm planning on doing something to help reduce the chance of that happening. There was some talk a while back about constructed links vs. tubular links, but I don't think I'm going to try to construct my lower links completely as suggested. It will likely be more of a sleeve, scab, or maybe a vertical separation approach.
     
  11. az-k5

    az-k5 1/2 ton status

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    Did you actually weigh the rig?? or did you just make an assumption based on known wieghts (engine, tank seats ect) and threw in a little room for error?

    Have you thought about changing your wheelbase (longer) to give you a little edge on the roll axis? This would also lower the rear steer issue, and take a bit of side load off of the rod ends. It might screw up the antisquat, (or casue you to move the upper frame mount up into the passenger compartment). I am not a link guru by any means just another party offering their views. I will be looking foward to the progress.

    Keep up the work.
     
  12. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    No, didn't weigh it or calculate the exact CoG, so it's all just "in the ballpark" stuff anyway. As you said, just figured approximations.

    [Edit] Oh, and that weight CoG is my guess for fully loaded with tools, parts, and 4 full seats. If anything, I may be a little low of full max load with 4 seats, but a little high for 1-2 in a seat and minimal gear. So I'm sorta figuring on the happy ballpark median since it can change so much based on loading.

    And I did think about changing the wheelbase. 113-115 is the range I would like to stay within, but that's not set in stone. I've seen very impressive results from Matt's 135" monster (Orange Ford), but I've also seen him and others with longer wheelbases struggle in places I had no issues. On the other hand, I seem to have been developing a desire to climb things, and I've been flat out spanked by a few rigs with slightly longer wheelbase (which seems to be the primary contributor, although maybe I just can't drive :crazy: ).

    On the forward link locations, they are actually pretty low in the frame could use moving up. But that has major bad effect on the numbers. I've got them as low as I think I can reasonably make them without building a sub frame.

    I guess I'm not too concerned with the antisquat assuming I have something close on the weight/CoG. Several people who have done the numbers (and the actual measurements) are running numbers like that and it works very well. I think it was Brandon who said he didn't like his at close to 100 AS but felt much better around 130 (rough numbers from memory, and maybe thinking of someone else). And I've planned a few adjustments just in case my guesses are too far off. Basically I'll have at least 2 slots on the diff, 2 or 3 on top in front, and maybe even one on the front bottom. And worst case, I'll rip out the front and redo a subframe or something if I really want it to go down further than I can do it with a simple mount.

    Thanks much to all with ANY input. At this point I want any and all input on stupid things I've overlooked before I start cutting up my precious gold alloy steel (that is why the price has got so high, right?) and wasting many hours which are in so short supply lately. I pretty much always find things I wish I knew earlier or had done differently, just trying to reduce that pattern on this project.
     
  13. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Seriously guys, I'm interested in your thoughts, it does not have to get way technical. If you think a longer wheel base will make a better compromise, tell me, and tell me why. Or even "I don't know how you would do it, but I would find some way to get that roll axis below 4* oversteer because..." Or "With that roll center height combined with the AS your going to ..." Even, "If it were me I would cut the frame rails off and retube the whole thing because..." (anything more substantial than "just because I would")

    Any thoughts at all???
     
  14. miniwally

    miniwally 1/2 ton status Premium Member

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    Russ move the axle end of the lowers up to the centerline or above the axle.

    Stephen and I both have this and have given things about the best stress test possible and they do hold up. I have the famous 1 3/4" .375 wall lower links and have bent both of them pretty good. They bend in a big arc not dent and kink. I am going to try the 2" .250 deal and see how it works.

    If you can build in multiple mounting points every where. I have played a little with mine and it seems to help tuning.
     
  15. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Thanks!

    They are already on the horizontal center line, I guess you mean put them on the vertical center line above the axle?

    Well, I'm using the big joints and 2 x 0.250 links, so if they are holding for you guys, I may just go ahead and try it. As I said, I was a bit concerned, but probably over thinking things. Also, my junk is heavier than either of your buggies I think. Still, by the time I add a bit of material to the lower links, I should have plenty of safety factor (I hope).
     
  16. PJTPW

    PJTPW 1/2 ton status

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    I would cut it off behind the cab, and tube from there. There are less limitations, shouldn't take too long, and you get to build more of what you want without as many compromises.

    That's what I plan on doing to mine. All the frame behind the seats will be gone. If I don't just build a full out buggy.

    I bet you weigh about the same or less than Stephen. I think he's in the 5200 lb range. I know Brandon is in the 4300 range with his buggy.

    As for wheelbase, the longer the better in places like Moab. My thoughts are the lighter it is the shorter it can be and retain the vertical ability. Heavier, a longer wheelbase does better.

    Also there is the breakover angle to consider, especially if you do a lot of waterfall / ledge type obstacles.

    Mine's 125" and weighs 5080. If it weighed 4300, I'd make it around 115 like Brandon's.

    To get around the drive train / driveshaft issue you could run an intermediate shaft off the t-case and then drop down to the rear axle. I have a 18" midship shaft in the rear which greatly improves breakover with the driveshaft, and allowed me to run identical shafts front and rear. It could be beneficial if you're concerned about link interference.

    Ryan
     
  17. yunit

    yunit 1/2 ton status

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    What size ZJ coils are you going with? I plan to use 8" front 4.0L TJ coils on the rear once I finally gettign around to linking it out.
     
  18. sled_dog

    sled_dog 1 ton status

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    I'm going with ZJ v8 coils, I'd guess russ is doing the same, but I may be wrong. My plan is building as much adjustability in as I can. Probably gonna man up and buy big joints for my lowers. Where are you getting yours Russ? With the 3/4" heims I have I was thinking about 1.5" .250 wall, sleeved with 1.75" .120 wall. We will see what I decide for rod ends, I have a feeling this rig will get as familiar with the skinny pedal as my balls will allow so beef is best. As for your exhaust, can't you just rout it up behind the seats a little? You'll lose a little cargo space but is that really so big an issue?
     
  19. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I actually debated long and hard about cutting off the frame and retubing. Almost did and even started making some sketches. But the final result was that it would require a fair bit of steel and engineering due to my need for torsional load of the upper coil mounts and something to support the mounts for the rear of the cage. Either that or I would have to redo the cage/body to eliminate the mounts so that the cage/chassis becomes integral, and it would take a fair rework for me to be satisfied with the cage/frame tie-in (i.e. suspension supports to deal with flex inputs). So I decided to live with the compromises, and hope that I get through this funk and start feeling more energetic about starting a buggy. For now I have to actively work at generating enough enthusiasm to do this much. If I don't run across a new and compelling reason to cut the frame, I guess I'll just save my steel and energy for the next project. For now it already gives me a strong mount for the springs, shocks, cage, and rear hook point without doing more work or using precious steel.

    Probably right about the weight, but Stephen has more "body" and tube than I do along with that big block. Then again I have more frame left (I think) so who knows.

    I think I agree with you for the most part on the wheel base. Maybe I will think a bit more about lengthening it out a bit. Break-over is obviously an issue, but I've seen several VERY capable trucks deal with it quite easily enough. Hmmm…

    Yunit:
    Yes, the are V8 ZJ stock coils. 13" compressed with the truggy rear weight sitting on them.

    Sled:
    I actually wound up getting the from Blue Torch. They gave me a great price so that I got the nice FK joints for about the same price as most places had the QA1s and other imports. Already got them setting here. In the immortal words of Neo, "Whoooaa!"

    On exhaust, remember that I have rear seats too. By the time you get behind them, it's a moot point anyway. I've also got plans for the rear center too, so it's not really practical to go down the center. It's one of those things I guess I'll wait till I get a mock up and see what works out. There are several places it will sorta fit, but it's going to take a significant convolution of bends if I can't work out a more direct path.
     
  20. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Brandon, what did you wind up liking for the AS? What about roll axis? What does Stephen like/run? I'm thinking around 135, but moving the lower links up a couple of inches brings AS back down to 111 or so and it is actually hard to get back up without causing problems or major changes that will be more difficult to implement... <sigh>
     

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