Bio Max Nash 4 link

I was curious as to why the upper bar on the 4 link is so short and angled down (least it looks that way in the photo)

is it just to keep the rear end in place and from rotating and doing the bars like that, isnt that along the lines of a ladder bar type suspension ?

I think he did that to keep the back seat there is a thread about bagging a blazer that he mentions it.

The suspension has good geometry for about 7" of travel, then it goes pretty far south real fast.

Yeah thats alot like my blazer> i had to use real short uppers on it in order to get enough triangulation. Pinion is fine from laid out to about 7-8" travel, then its fucked. But the only time it'll be lifted over 5" is when I need to change a tire. haha.

When designing a 4 link with such short top bars is there any particular method??  I know with relativly even length bars you use the instant centre but in this case the short top bar would be taken into consideration some how wouldnt it?

The travel and the relationship of the 4-link to the travel is far more important with short bars. I make sure that the short bars are parallel to the ground a half travel and angle the lower bars so that it has a properly placed IC.

this info helps alot btw did you mean "angle the lower bars" ? or was that a misprint?

The lower bars will angle up so that a line drawn through them will intersect with the parallel top bar line and give you your Instant Centre(if your looking side on)   Ok so far i have put this into my CAD model to try get it to work and so far i hav 6 degree pinion change over 7" and a lot of drive shaft movement.  My best result so far is from running the bars parallel at 3/4 height but then the IC at 1/2 height is quite long and low.    

You guys and your fancy CAD programs!   That would be just fine. My suggestions are just good starting points, not scripture! I have never been able to play with any modeling programs, so if you find something neat-o please share.

Edited: 3/5/2009 3:53:52 PM by SHIFTBOY

HAHA mine isnt fancy, its the 2D plug in to sketchup pro called SPIRIT,  i have just made various templates of rearends, wheel sizes and chassis. I just make radial circles from the chassis end of the link and copy and paste the rear end through the various stages of the travel to see what its doing.  I started doing it this way to take some of the guess work out of designing 4 links and just lately i have been sending a lot of the drawings to the CNC bed to be cut out so we can pre-fabricate to a degree.