[zookernator]

Hello!! As most of you's know, im currently doing a 4 link conversion in the rear of my 1991 sierra. I've got all of the control arms, coils, coil mounts etc figuired out, but i just started playing with the 4link calculator - and buggered if i can get my head around it!! It appears that i need the following measurements for the calculator to work: Front and the rear un-sprung mass, the vehicle mass, the COG etc. But, the cab needs to be on for me to be able to get most of these measurements.. but i have already got my cab off!! I also cant figuire out all of this X Y Z stuff either Can anyone please give me some advise?? Thanks heaps

[jdk81]

I haven't done this mod before, but can do the theory.

you can work out the combined CoG, using parallel axis theorem (or centroidal axis theorem).
http://www.efunda.com/math/areas/Parall ... heorem.cfm

calculate the CoG of the chassis, engine and drive train etc
calculate the CoG of the body.

unsprung mass is the mass of the rear diff, tyres, brakes, and 2/3 the rear driveshaft, and everything else on it.

Unsprung on the front is diff, tyres, brakes etc, steering crap, and 2/3 the front driveshaft.

x y z will be the axis.

if you want, send me all the formulas and measurements, and ill see what i can do

[just_cruizin]

Front diff about 50kg
Rear diff about 45
Tyres about 15 - 20 or more depending size
Drive shafts don't worry about because the other's are guess anyways
COG I would put somewhere about level with the front edge of your door and slightly to the drivers side by about 50-100mm and about floor height maybe a tad higher.

These are only guesses but the position of your mounts will be compromised by where you can put them anyways. Just do like most of the buggy guys do and make mounts with heaps of holes for different adjustments. Even if they are only temporary, between what works on computer and what works out on the rocks(you shouldn't be driving tracks) will be different anyways.

[11_evl]

from my quick estimates.

diff link seperation=9-9.5" (for a 37" tyre)
lower control arm length about 5-10 deg up or down from diff to chassic pending on what way you take it from, than where it meets the frame is how long your lower link needs to be.
than you make the upper link 70-80% of that length
the link seperation at the chassic end needs to be about half the diff end eg 0.5x 9-9.5", but im going to make that sit whereva sits best
im going to make my lower arms mount inboard of the chassic rail to outter diff
than as far out on chassic on top to center of diff
aim for about 40deg angle in for the upper arms

thats basically what i got from reading an article

[31zook]

I myself have never done it before but this is all the theroy behind it. you can actually do a full drawing with just this write up.
4-link tech

[31zook]

also it has been suggested that a good guide for finding you COG is the top bolt on the bell housing...

[zookernator]

Wow.. thanks heaps for the replys guys!! Kind of makes more sense now.. Thanks for the link 31zook.. heaps of info in there!! I'll go back up and take some more measurements in an hour or so..

[zookernator]

just_cruizin wrote:

Front diff about 50kg
Rear diff about 45
Tyres about 15 - 20 or more depending size
Drive shafts don't worry about because the other's are guess anyways
COG I would put somewhere about level with the front edge of your door and slightly to the drivers side by about 50-100mm and about floor height maybe a tad higher..

Im running bundy/lux diffs with 35"s (steel rims), So would it be safe to say that the front would be approx 90kg unsprung, and the rear approx 85kg unsprung?

[zookernator]

31zook wrote:

I myself have never done it before but this is all the theroy behind it. you can actually do a full drawing with just this write up.
4-link tech

I think for now im going to just work from this article. Just for interests sakes, this is the "proposed plan"..

[11_evl]

i like your upper diff mount

[zookernator]

11_evl wrote:

i like your upper diff mount

Should do the job hopefully.. i beefed up the guts of it to...

[1jzjzx90]

cut first measure later

[just_cruizin]

May want to add some drain holes.

[31zook]

nice, as i said before im not a link king or anything, but do you think that there will be allot more pressure mounting the upper and lower arms so close on the diff? If you read the info it says that about 25% of your tyre size they should be apart.

so if your running 35s they need to be 218mm vertically apart.
And your upper and lower control arms control your anti squat. This is needed for whether the truck stands up or sits down as you accelerate.

jmo

[zookernator]

true true.. i have read that in some of the articles. Those pics above are just a very rough idea of how it might look. I am currently doing all the calculations/measurements at the moment.. and obviously that will change things dramatically!! Thanks matey..

[93zook]

i would say you need alot more seperation on the diff end for sure. whats ur current chassi hieght??

[11_evl]

31zook
i was going to say that as well but im sure he is mounting the lowers lower on the diff. id say level to the bottom.
i think he has the arm sitting there for pic and angle purpose.
lowering the bottom link and raising the top should be about right.

[zookernator]

93zook wrote:

i would say you need alot more seperation on the diff end for sure. whats ur current chassi hieght??

yeah.. it seems like the calculator will tell me exactly how far apart they need to be.. i hope The chassis height at the back is 760mm..

[93zook]

im not sure if it will tell you that but i havn't messed around with it to that extent, how far back is the rear diff moving?

[31zook]

zookernator wrote:

93zook wrote:

i would say you need alot more seperation on the diff end for sure. whats ur current chassi hieght??

yeah.. it seems like the calculator will tell me exactly how far apart they need to be.. i hope The chassis height at the back is 760mm..

bottom or top? because thats real high... you might want to lower it a bit...

[zookernator]

31zook wrote:

zookernator wrote:

93zook wrote:

i would say you need alot more seperation on the diff end for sure. whats ur current chassi hieght??

yeah.. it seems like the calculator will tell me exactly how far apart they need to be.. i hope The chassis height at the back is 760mm..

bottom or top? because thats real high... you might want to lower it a bit...

thats at the bottom. Im hoping to lower it all a bit during the process. Anyways i just went and did some more measuring. I will be able to have 900mm long lower arms, and approx 600 long upper arms. This is very close to the 70% that is needed.. so i am going to play around with this article again http://www.muddtanks.com/4LinkSuspArticle.htm This seems like the most user friendliest one i have came across so-far!!

[Ridge]

what is going to happen with your fuel tank, it must be a very tight fit? from what i have been reading so far uppers 70% of the lowers is ideal but you can go another 10% +/- I am keen to try jackaroo lowers (~ 870mm) with gq lowers (670mm) used as uppers which will be 77%.

[LAY80N]

Try to increase your vertical serperation on your diff end, it should be double what you have at the chassis end. Vert seperation should be approx 1/4 of your tyre size at the axle end, and 1/8 of your tyre diamiter at the chassis end. This difference ratio will allow your suspension to change its squat/anti-squat dynamically as it cycles, so at full squat your anti-squat ratio will help stop the suspesion trying to squat further, and at full droop it will decrease the anti squat to stop the suspension trying to top out. I hope that makes sense, if it doesnt email me and i can send you some more details (im in and out during the holidays so if i dont reply straight away i will at some stage later ). If i can find it i will post up the calculator and solid works screen shots of the last 4-link i build.

Quick photo - the rear diff truss is about the height of where the link is sitting in the photo .The vert seperation on the Axle is 267mm and the frame end is 127mm. This truck will run 42 irocs and have a supercharged 1UZ lexus V8



Will get a better pic now when im next working on it. The link mount inside the chassis rails.

Layto....

[zookernator]

Layto.. thanks heaps matey, that actually does make sense.. 2 weeks ago it all would have been a big blur though!! Thanks for the good explenation though.. made heaps more sense. Good luck with your build.. oh, and we want more pics and updates!!

[zookernator]

I have been playing with the calculator and measurements a bit more.. and these are the latest results. I have done some research and altered the weight, and also managed to get a better anti-squat number. By rights if i outboard the chassis end upper arms an inch or so, the roll axis should become into a happy range.. will play around again t'row and see Oh.. and merry christmas!! woo hoo!!!!!!!!

[LAY80N]

Better late than never

Layto....