4 link help

zukijames

zukijames

Well-Known Member
Location
not moab anymore
rebuilding my zuk..and need some help
6f86fe34.jpg
here are the measurements i have..
now i did some homework i realize i need more but i dont get it and know a few of you on here are pros with the junk

.axle upper link mount 32"
axle lower link mount 20"


frame upper 33.5
frame lower 24.5

lower axle link mount to link mount 46"
upper axle link mount to link mount 6"

lower frame link mount to link mount 10"
upper frame link mount to link mount 38.5

lower links joint to joint 47.75
upper links joint to joint 38"

frame height :21"

tire size: 40
weight: 2500-3000?
wheel base: 112

top of bell housing 36-40? im guessing on that one
unsprung weight? fj 80 axles idk lets say 1000?

what else do i need to measure to plug into the link calculator? anyone that would be willing to plug it in for me if i get the measurements..

i mounted my lower axle link mount on top to the axle.. so the upper link mounts are perpendicular to the lowers is that a problem?

this picture is before i mounted the upper but its sitting in the same spot. you can see the lower axle mount on top of the axle. i know one of the x's or y's is from lower link mount bolt hole to center line of axle of upper link mount hole i couldnt tell in the picture but mine will be at 0 is that a big problem?
rearlinks.jpg
the rig is in west jordan will be working on it tomorrow 8018859813 if your bored and wanta give some suggestions feel free to some over
 
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I couldn't decipher some of your post. You need significant vertical separation between the upper and lower link mounts, so by mounting our lowers so high, you will need to mount your uppers pretty high as well. Build it at full compression so you know nothing is going to hit. Your uppers are going to run from somewhere around the frame, to the center of the axle?
 
should be a little easier to read now!

.axle upper link mount 32"
axle lower link mount 20"

so at the axle end my lower mount is 20 inches from ground and my upper is 32

is 12 inches of separation on the axle


frame upper 33.5
frame lower 24.5

and 9 inches of separation at the frame end would like more but probably wont happen


also right now my lowers are on like a 4 degree angle going up .. is that too much?

thanks for you help, sorry it was so hard to read before. I'm not sure why after i edited it last night it made everthing a big run on sentence
 
The axle separations and the frame separations all look good. A rule of thumb is to have about 25% of your tire size equal the axle separation. So, for a 40" tire you would want 10". On the frame side you will want 75% of the frame separation or there abouts. So, again with your 10" at the axle you are going to want about 7 1/2" or some where around there. I learned that four linking anything is all about compromise. Don't get too wrapped around the axle if you can't get everything perfect. Sometimes close is all you are going to get. So don't worry too much about it.

LT.
 
when i cycled the suspension it seemed to have alot of umm rear steer? with my old suspension the tires didnt move forward or back at all why cycling just up and down.

could the be because my links are too short for how far they are angled in? 47 inches long mounted 46" apart on axle and only 10" inches apart on the frame end?
 
Are the uppers mounted already? If not, when that happens it should help with the tire movement. Similar lengths or arms will help too.
 
If it were mine I would lower the uppers at the axle end a couple inches to bring them closer to parallel with the lowers. Your lowers are not at all too steep.
 
How do you figure out how long the arms need to be? Other than a link calculator is there some formula or something to figure the lengths? And what about if you have them triangulated or not?
 
Cascadia said:
How do you figure out how long the arms need to be? Other than a link calculator is there some formula or something to figure the lengths? And what about if you have them triangulated or not?
Click to expand...


i made the lowers as long as i could :) and the uppers 80% of that lol sure thats not the proper way to figure it out but yeah
 
Cascadia said:
How do you figure out how long the arms need to be? Other than a link calculator is there some formula or something to figure the lengths? And what about if you have them triangulated or not?
Click to expand...
There is no reason the uppers have to be any particular ratio of length as the lowers. Lots of people say 80%, with no justification. If they are different lengths they will travel in different arcs, so the pinion angle will change throughout the travel of your suspension. this can hurt you, or help you. Having the uppers shorter will move the pinion down as the suspension extends, and up as the suspenion compresses, which could prematurely wear, or bottom out and destroy the u-joints. I like to make my uppers as close to the same length as the lowers as possible, and close to parallel.
zukijames said:
so put the same angle on the upper as the lower? the upper is 0 degree and the lower is 3 or 4 cant remember
Click to expand...
Yes. That will move your instant center forward, and lower anti-squat. I've seen lots of negative effects of too much anti-squat, but never seen a problem due to too little anti-squat, on a rock crawler. Are you able to get full compression with the upper links tht high? The are triangulated to the top of the differential, right? Making the uppers longer will also likely solve your rear-steer problem.
 
no i have an offset dif.. but yes uppers are triangulated .. i want 80 percent to make the dif move with the suspension.. its a short drive line and with the offset i need to get it pretty close to perfect..

if they uppers were the same length wouldnt it point the dif up during compression binding my u joints?
 
My uppers are the same length as my lowers and my pinion points directly at the t-case throughout the entire suspension cycle and my rear drive shaft is only 29 inches long
 
is there such a think as too much separation? also i could lower the lower link frame mount another inch or two (and still keep a flat belly) and that would also move my center line or w/e its called where the two lines would meet. and get my lower links flat instead of 3 or 4 degrees

but i dont know if lowering that lower link frame mount would screw anything up is it better to have it high or low? i was thinking the higher , flatter, and more separation where some of the main things to go for
 
NO, don't make them equal/parallel. Your rear suspension would squat really bad. Desert racers can get away this much squat, but a crawler will have a hard time getting grip.
1. axle separation looks ok. between 10-12" with 40's will work. You will get a little more roll understeer with 12" and it raises your roll axis a bit. If your going for super flexy you may want to go with 10" separation.
2. link separation at frame basically determines the squat characteristics. Equal separation basically gives you no anti squat, and as you move the front of the links closer together you will add anti squat. What to shoot for is largely up to what you want out of your buggy. The front upper link mounts are where I would build in some adjustability. If you give yourself 3 or 4 mounting points you will be able to dial in the squat charachteristics you want, many times you don't really figure out what you want until after the build is complete. I personally don't like rigs with tons of anti squat, so for me I would put my adjustable holes at equal on the highest and 3-4 inches down on the lowest. With your link lengths that will give a pretty wide range of adjustments.
3. upper link length. It seems that around 70% keeps your anti squat equal throughout vertical travel, this is why you see this # talked about so much. Yes, it does induce some pinion angle change. That is the trade off for correct suspension geometry. Many desert/go fast link setups use a length that has the anti squat lessen as the suspension droops out and then get greater as it aproaches full bump. This gives a certain amount of "bump stop" built into the system.
4. lower link angle. you want the virtual point that the upper/lower links make to be around the center of gravity. Having the lower links angle up a bit will help raise this point up where it needs to be. If the lowers are parallel to the ground this point ends up being quite low.

I think that your basically on the right path with your first plan. I would go with around 10"-11" separation at the axle. I would make adjustable mounts for the upper frame with 10"-6" of separation, so you can dial in the antisquat at a later date. I would mount the lower links even with the axle and let them angle up so that the point created by the uppers and lowers is around the center of gravity. I would try and shoot for making this point at the area around the front bumper. The adjustable front upper link mounts allows you to move this point forward and backwards, testing will show what works best with your rig.
At some point you just have to burn it in and see how it works out!
 
Dont over think it. You will never get all your numbers to be perfect. Put the link mounts where they fit and they are tucked up out of harms way and go from there. You could write a 40,000,000,000 page book on link suspension theory and still wouldnt make all your numbers perfect.

It seems like you have done your fair share of research so run with it and dont second guess yourself.:)
 
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