Designing four bar links

I've searched the archives and I've not found much on length or links.

On my Ford 9" I will be using split bones with pivots on both ends for the lower links but the issue I'm having is the minimum amount of room for the top links. I can not fit links any longer than 8" for the top set.

Is this OK? I've drawn out the swing arch of both top and bottom and it does make things move forward a little bit at the top. I am running a model A rear spring and am worried about tweaking the spring by pulling it forward when the suspension compresses.

Should both links be parallel at rest and whats too short?

My total amount of suspension travel will only be about 3.5"

I need help from you suspension gods!

Thanks,
Motor

 

if you over-rotate the axle as it compresses you'll not only potentially root the spring, but your pinion angle will be mighty fucked up too. as i understand it, you want to set the pinion angle at the diff the same (but opposite) as at the gearbox, around 3° is the figure you want, from memory.

if you twist the axle, say, 3 degrees as your use your travel, you'll potentially suffer from drivetrain vibration, and possibly kill the uni's...

i have no idea how much lateral movement the spring can withstand before damaging itself though...

 

I'm definitly not a god, suspension or otherwise, but you could try mounting your top link pivot behind the axle rather than the usual front fitment.
Not too clear a photo, but I was in the same dilema as you: no room, and decided to reverse the axle mounting bracket, which gave me an extra 4" length for the four bar rod. The brackets I used are actually a bit small. Doh. Not much clearence for the link bars.

A better way for you would be to use a single central triangulated pivot on the top, above and behind the diff housing maybe, which will steer you away from the binding you will get with an unequal length four bar system.

Use soft rubber bushes in your spring mounts to allow a little flex. Someone mentioned rubber hose as bushings on here a while back.

 

This is some great advise.

What do you guys think of the new Posies super swivel type links for 1/4 eliptic springs they are now offering? That would make a nice flexable connection.

Motor

 

This is what I was thinking about.

http://www.posiesrodsandcustoms.com/category/posies-product-releases


I could use a swivel above the pumpkin on the triangle shaped top link.

 

bttt

 

I think the best deal is to set the pinion angle so it is correct at normal ride height. A little error doesn't really cause a lot of problem.

 

Anyone else have $.02 ?

Bueller?.. Bueller?.. Bueller?

 

I could use a bit more input.

Does anyone have drawings that show how to set up a triangulated four bar properly?

Thanks,
Motor

 

I'm going to use the same setup (Split '36 RR w/ pivot under axle, A spring, open drive) and I did a drawing with the radius rods cut 2 27", and 10" bars on the front of the axle tube, with 8" of travel (4" +/-) from ride height, the axle changed 4 degrees at the bottom and 2 degrees at the top of the travel.

I can draw, I'm not an engineer... Assuming that the total amount of travel out of that A rear spring is about 4" (2" +/-), and the most pinion angle change is 2 degrees, is that too much?

Of course I didn't save the drawing, that would be smart.