How's this suspension working?

Just added a 4-link to the race truck.  Analyze this launch for me guys.  What's it doing?  What is it not doing that it needs to be?

This clip was filmed on 1080p @ 60fps. I then slowed it down to 24fps w/ my GoPro software. Next test session will go from filming @ 240fps down to 24fps!

IMO the diagonal link mounting (if the centering device is a diagonal link and not a panhard bar) should be changed since it's not sitting "on-center" with either the top 4-link bar's C/L, or the bottom 4-link bar's C/L.

Usually a simple diagonal link is mounted below the housing (on a drag car anyway) & it's C/L is mounted directly on-center/in-line/on-plane with the bottom 4-link bars (so they all travel in the same arc). If the diagonal link's C/L is mounted on a different C/L arc than the bottom 4-link bars (or the top 4-link bars if mounting it above the housing) then the diagonal link can pull the housing to one side (and/or bend the bar) as it goes through the suspension travel from the two different arc's fighting each other.  


And if the centering device in question is really a panhard bar (and not a diagonal link) they are usually mounted parallel with the rear housing's side-to-side C/L above the housing, and not on a diagonal angle.

This will be for a mud race truck, Running some rough pits. Would a panhard be more favorable than a wishbone? Or would any other style be better for locating?

My long winded housing centering devices pecking order breaks down something like this for drag-only and street driven cars (may/may not apply to other types of racing vehicles too).

Simple single diagonal link........
Simplest centering device for drag racing. it doesn't have slip joints that need to be cleaned & greased regularly (so lower maintenance). It's C/L must be installed on center with either a 4-link's bottom, (or top) bars front/rear pivot points, or on center with a ladder bar's bottom bars/front pivot points. When installed correctly it keeps the housing centered throughout the entire suspension travel without pulling the housing to the side. it's mounting brackets can either be bolt-on (used with both 4-link and ladder bar, & bolted to the housing/chassis brackets) or weld-on (used with ladder bars only, & welded directly to the LB's lower bars). It can't take much suspension side loading without bending (even with a large OD bar), so it's really not the best idea for street use in most cases.  

Double diagonal link.......
Basically similar to a single diagonal link but with two smaller (or one big) bar/bars going the other diagonal direction (joined in the center) so the assembly forms an "X". Some people call it an X-link but since it's center is joined by clevis's and/or rod-ends (and not a welded structure) it's really just two diagonal links overlapped to form an X. Just like the single diagonal link the double is great for drag use, needs to be installed on-center with a set of suspension bars front/rear pivot points, doesn't have slip joints or need to be greased, and won't pull the housing to the side if installed correctly. While the double does form an X and can handle higher side-loading forces than a single, it's still not the best idea for a truly street driven car that is driven hard (cornering and such).


Panhard bar.......
IMO a panhard bar is the #1 best all around idea for centering a housing on a truly street driven car, or a car that sees high side loading/cornering forces. It's a simple low maintenance design. And as mentioned earlier it's installed parallel with the housing's side-to-side centerline (not diagonally) , one end to the hosing, the other to the chassis (the longer the panhard bar the better). It's usually mounted above the housing on street use and/or pro street stuff, and somewhere behind the housing on the NASCAR type stuff (they call it a track bar). It does pull the housing to the side a given amount during suspension travel, the shorter the panhard bar is the greater the housing is pulled to the side. And because it does pull the housing to the side it's not really the best idea for a drag use car. But that's not to say you 100% can't use them on drag cars, some people do.

Watts link......
The Watts link would be the #1 centering device for street use if it wasn't so much more complicated, and if it didn't take up so much more room under the car than the other centering devices. It's basically two panhard bars mounted to each frame rail on the outer ends, and to the center of the rear housing on the inner ends with a bellcrank assembly mounted to a bracket. It's downside is it just kills so much room under the car. If mounted above the housing with the bell crank mounted horizontally, it kills a ton of room that could be used for more suspension travel. And with the bellcrank horizontally mounted that suspension travel could be limited anyway because of rod-end binding since the housing is moving vertically. If mounted behind the housing (and the bellcrank mounted vertically) you gain back the lost suspension travel & reduce the chance of rod-end binding, but loose the space where the coil over shocks would normally be mounted.

Wishbone........
IMO the wishbone is the 2nd best idea for a drag car (when installed & maintained correctly). Stronger than a simple diagonal link AFA side loading goes. But it does have a slip joint that needs to be cleaned & greased regularly so it doesn't seize up & put he suspension in a bind. Some people do use them on the street, but street use means they must be checked even more often to keep them clean/greased. They form a basic triangle & can be mounted facing backward, (2 pivot points on the chassis + 1 pivot point on the housing) or forward, (1 on chassis + 2 on housing) and either above or below the housing. The slip joint is on the end with only one rod-end/pivot point. Since it uses a slip joint it doesn't have to be installed "on-center" with the centerline of a set of suspension bars like a diagonal link does. It keeps the housing perfectly centered, and does not pull the housing to the side like a panhard bar does.

X-link......
IMO the X-link is the #1 best idea for a drag car (when installed & maintained correctly). Similar design/attributes as a wishbone but with a 4th leg & 4th rod-end added so it's an "X" shape vs a wishbone's triangle. The slip joint is in the center of the structure (think two triangles facing each other with a slip joint between them so the whole structure forms an articulating X). And just like a wishbone the X-link doesn't have to be installed "on-center" because of it's slip joint, and it doen't pull the housing to the side. The downside to an X-link is the same as a wishbone, the slip joint that must be cleaned/maintained.



Power link/swing arm & true swing arm.......
Also somewhat in the mix is the solidly welded X bar setup (with no slip joint) that is welded directly to the lower 4-link bars making the bottom 4-link bars and the centering X one solid/rigid assembly. On drag door cars this setup is usually attributed to the Auzzy Pro mod chassis builder Murray Anderson and called a "Power Link" 4-link setup. The dragster guys call this same setup a "swing-arm" 4-link setup (incorrect term IMO since it's not a true "swing arm").

A true "swing arm" drag car suspension is what some of the older Pro Mods used years ago. It's design is also usually attributed to Murray Anderson as well. It's design is in effect two long 3 bar ladder bars attached to each other with a large center X welded solid to each ladder bar making one large non-flexing assembly (and unfortunately with little or no adjustability).


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I guess because of the conditions a mud/dirt truck operates in IMO I'm kinda thinking you throw out any centering device design that uses/has a slip joint because of the mud/dirt getting in the slip joint & seizing it up. You also probably throw out the diagonal link because it can't handle much side loading. That pretty much leaves the parallel mounted panhard bar because it's simple & can handle higher side loading. I don't know for sure, but I would guess the amount it might pull the housing to the side might not really be a problem in a mud/dirt pit as long as it's not made too short.

Dave,

Thanks soo much for taking the time to post the info here.  That takes a lot of time and it is greatly appreciated.  Looks like the diagonal link is coming out and a long... As close to horizontal as possible pan-hard will go back.

Thanks again for all the info and hard work!

What do you think about the separation we got at around 130%AS?

Jon

460bronco wrote:........What do you think about the separation we got at around 130%AS?.....

I don't have any idea how much initial suspension separation a mud/dirt truck might need at the hit, the application is just way too different from a drag car. Only thing I can say is don't forget that any given anti-squat number isn't the only thing that has an effect on rear suspension separation actions (how much & duration it lasts) at the hit. Shock valving stiffness adjustment & actual engine torque numbers (during the hit) also plays a part too.