Triangulate 4 link on FRONT??? Sketches/ideas

[kelseydum]

I've been researching this and only seems that off road vehicle use this. Can this work for a street rod with an I beam axle up front? In theory ( in my head) it seems like it would be a good thing but I don't have a degree in mechanical engineering. Check out my pic... If it works. I also have some skeches in progress for an I beam radius rod with lightening holes.

 

[kelseydum]

Here is my custom i beam radius rod idea. Probably just try steel first but I'm wondering if aluminum would work too. It would be some work but fairly cheap and really cool... If they would work.

 

[YBeNormal]

Are you trying to set it up to run air bags in the front?

 

[zzrodder]

I've seen various 4 link versions on lifted/rock crawler newer Jeeps. Probably the reason it's not seen as much on rods is the packaging problems what with the 4 link bars, steering, rad hoses, shocks, springs, engine mounts, fan etc. all wanting to fit into the same space. Sometimes it's simpler to just make the lower links solid mounted to the axle like split early Ford 'bones' and use a panhard bar.
Can't remember the the build title but I think his handle here was Bustedknuckle, a late 30's or early 40's pickup build with a wild 4 link front end with bags.

 

[kelseydum]

Yes I forgot to mention the air bags but guess you could tell in my drawing. I'm also running cowl steering and so far I think this could be a very plausible set up.

 

[YBeNormal]

Yes I can see where it will work. The air setup you are trying to run is similar to mine. I am using a Cenpen unit so to square mine we pushed the axle out in front on the grill and just used a pan had bar. Seems like it will work.

Your setup will be different and that's what makes all of our rides unique [S

 

[Dirtyrat]

Depending on the axle you use, you can triangulate the upper arms at 20 degrees similar to the method I have used. (In my build thread this work started on page 62)

 

[Sam_Fear]

Since the triangulated 4link works because of "give" in the bushings, will that same "give" introduce looseness and a possibility of wobble in the steering?

 

[kelseydum]

Yeah, I'm wondering if it would be too stiff since the I beam axle is supposed to flex unlike the tube axle and if I run wishbones or hairpins there will always be chance for caster change with the suspension travel whether I add the two extra bars or not. I'm doing a lot of mock ups on paper... But we all know things can change when you get on the road.

Also, many people just throw some airbags in and go. I'm doing a lot of research to have the bags run at optimum ride height, stiffness etc...this should minimize suspension travel which helps eliminat hanged for other steering issues.

 

[Dirtyrat]

My caster does change when going over bumps, but its a positive caster change, and it is very limited. (spring gets longer on travel)

 

[wendle]

Your front 4-link will work OK if the drag link is the same length and parallel to the lower links.
If it doesn't meet both these requirements it will bump steer quite a bit as the drag link moves around a different axis to the axle.

Your caster change as the axle travels might be a bit severe with such different length upper and lower links too. This can work pretty well in the rear of cars if planned out to keep the pinion pointing where you want it, but the closer to equal length in the front (generally) the better.

Another thing to think about is that any slop in the bushings will equal slop in the steering, that's why OEM Panhard bars use metal/metal tie rod ends, or quite hard poly bushings. Sometimes even bronze bushings.
These will give you a pretty harsh ride in your 4-link bars, might as well just use heims.

One nice thing with a 4-link front (even a parallel 4-link with a Panhard bar) is that you can tune in your anti-dive under brakes by playing with the vertical link seperation at the chassis end. If you make the upper link mounts adjustable in height you can change how much weight is transferred to the nose of the chassis under brakes, pretty cool

I've built a lot of front 4-link suspensions, but all in off-road cars with hydraulic steering, so it's kind of cheating.

 

[kelseydum]

Thanks for the info. My wishbones will use the heim joints and I have a set of Energy Suspension Polyurethane bushings that you mentioned.... The same that most places use on their 4 bar kits and has a metal inner sleevethat mounts to a metal bolt. If I can find he right wishbone my drag link and radius rods should lay at near exact same length and parallel. Also, to help eliminate any bump steer, the long length of the cowl steering drag link and wishbone will minimize suspension travel... Thus minimizing the arc of travel that plays a huge roll in bump steer.

I've don a ton of research on cowl steering and we all know the typical cowl steer set up initially breaks all the rules on steering geometry yet somehow seems to work really well... Some say better than traditional steering.

 

[kelseydum]

The poly bushings I mentioned will be on the end of the air bag cantilevers that mounts to the front crossmember and will use spring shackles and pivots on the ends that hook to the wishbones... Technically this would complete a "4 link", and I was thinking the two rods going to the custom brace on the front axle would be nothing more than EXTRA stabilization instead of using a panhard bar (actually creating a 6 link). This was just an idea I was throwing around to keep the axle from twisting.... But I believe the axle (i-beam) is supposed to twist so these extra 2 bars may be overkill and counterproductive.

Still trying to decide if I want to try it or not. Still in design phase.

Keep the good info coming guys.

 

[wendle]

The poly bushings I mentioned will be on the end of the air bag cantilevers that mounts to the front crossmember and will use spring shackles and pivots on the ends that hook to the wishbones... Technically this would complete a "4 link", and I was thinking the two rods going to the custom brace on the front axle would be nothing more than EXTRA stabilization instead of using a panhard bar (actually creating a 6 link). This was just an idea I was throwing around to keep the axle from twisting.... But I believe the axle (i-beam) is supposed to twist so these extra 2 bars may be overkill and counterproductive.

Still trying to decide if I want to try it or not. Still in design phase.

Keep the good info coming guys.

I'm not sure I've got my head totally around your description, but keep in mind that any suspension with more than 4 links will bind to some degree.
Even a parallel 4-link with a Panhard bar relies on compression of the bushings to articulate.

Basically, there is 6 possible degrees of freedom for a vehicle axle, and you want to take away all but 2 (vertical travel and axial rotation), so the magic number is 4
Unfortunately, this all gets compromised when you add in the need for mechanical steering linkage.

 

[Dirtyrat]

Also look to keep the location of the steering drag link pivot on centerline with the axle like a stock setup would be on an F-1 truck.

 

[King Herald]

Four bar front ends have been around for decades, so moving the rear ends of the lower bars inboard a few inches or more, under the chassis, is not going to be a major mechanical feat.

You can thus keep them all the same length as the drag link, cause not bump steer, and have a smooth running front end that doesn't take a year of engineering to produce.

The lower two bars could be connected to the cross member, in the centre if required, for lateral location.