school me on the "3-link"

[mopar_freak]

Ive been looking around trying to find some solid info on a 3 link rear. Theres some great info BUT Im a noobie so all the abreviations had me confused, except for the basic UCA, LCA, etc. Ive mostly been into jeeps and 4x4s, so getting handling out of suspension and not crazy amounts of flex is new to me.

Basically what Im asking is can some one point me in the the right direction for a basic break down of the whole idea. I mean I get it sort of but its figuring the geometry thats got me at a road block. Any way I know the LCA have to be parrallel to the cars centerline while at ride height, and the UCA has a 5-7* downward slope(im guessing toward the front) at ride height. I need help with the rest and any things I have missed. Dont flame me because I dont quite understand.

One company, XVMotorsports actually markets a 3 link rear for mopars, but it will probly be around 3grand after getting it to the islands. But it looks so simple I could build it myself for cheaper, just maybe not billett aluminum LCA, and aluminum coil over shocks that are tuned for b body suspension. Here are some pictures, I got off the net. And Im thinking build a suspension pretty much the same way, except beef up the UCA mount since XV mounts it to the floor pan.....

https://static1.pt-content.com/images/pt/2010/06/2003_09050023-1.jpg

https://static1.pt-content.com/images/pt/2010/06/2006_03020011_1024-1.jpg

https://static1.pt-content.com/images/pt/2010/06/2006_03020014_1024-1.jpg

https://static1.pt-content.com/images/pt/2010/06/cimg2353mediumbm8-1.jpg
So I figure use the same leaf spring mounts on the frame for the LCAs and I can make a brace attatched to the frame for the centerlink. Anyones help with the idea is appreciated.

[exwestracer]

You're basically correct in all your thinking. The LCAs should also be level with the ground at ride height. That may need some looking at if you are planning on using the stock leaf mounts on the chassis.

There's a recent thread here about triangulate 4 link suspension. Most of the comments run to the effect of UCA angle so that would be a good read for you.

In a nutshell, the lower links push the car forward under power, the upper link resists housing rotation (opposite reaction to tire rotation). With the link running down angle to the chassis, this will also provide some lift force against the chassis to help plant the tires. Under heavy braking the forces are reversed, so you really need to prioritize when designing the mounting locations and link angles.

I spend hours discussing this in my classes, and there are LONG pages of info on the Net. Going any further here is gonna take a lot of space... Billy Shope (member here) has a website with a lot of explanations of link type suspensions. Might be a good place to start.

[Rhino]

I'm not sure how deep you want to get into the design aspect, but here are a few of my favorite books on the subject.

Chassis Engineering by Herb Adams
How to Make Your Car Handle by Fred Puhn
Competition Car Suspension Design, Construction and Tuning by Allan Staniforth

[LSx_88_Ciera]

Here is a spreadsheet that will help with the influences link length and placement have.

[John Wright]

Huh, that Excel worksheet is neat....never thought about using a bar chart to plot all of that out...cudos to whomever built that worksheet.

[LSx_88_Ciera]

Huh, that Excel worksheet is neat....never thought about using a bar chart to plot all of that out...cudos to whomever built that worksheet.

Yeah it is a nice piece helped me out quite a bit, always nice to have a bit of a visual reference.

[mopar_freak]

yeah that 3 link program helps alot, exactly what you said some visual aid is good

[elitecustombody]

wonder if there is spreadsheet for triangular 4-bar

[John Wright]

Here's a 4 bar xls. sheet....

[mopar_freak]

how much room is needed for the 2 trailing arms for up travel?

I know its not a jeep, but i dont know how much up travel the arms are gonna be doin.

I was looking at Gforce designs Demon and I noticed they used a spring relocation kit as mounts for the trailing arms, probly to max out that mini tub. I was thinking of the idea before I saw the setup on the car. Im sure if they did it I can do it and it will be fine. But Im just curious because everyone on the board knows more than I do.

[exwestracer]

how much room is needed for the 2 trailing arms for up travel?

I know its not a jeep, but i dont know how much up travel the arms are gonna be doin.

I was looking at Gforce designs Demon and I noticed they used a spring relocation kit as mounts for the trailing arms, probly to max out that mini tub. I was thinking of the idea before I saw the setup on the car. Im sure if they did it I can do it and it will be fine. But Im just curious because everyone on the board knows more than I do.

Decide how much room you want to allow for axle travel (assuming nothing hits first). Usually 3 1/2" is sufficient. Measure how far your point of contact (first thing the arm will hit) is from the front pivot (spring mount). Whatever fraction that is of the total length of the arm is how far the arm will move at that point.

Example: Arm length is 24" from mount to axle, the contact point is 6" back on the arm, or 1/4 the total distance. If the axle moves 3", at the contact point the arm will move 1/4 that much, or 3/4". As long as you have more room at that point then the movement of the arm when the axle bottoms out, you're safe.