Can I run the top bars of my triangulated 4 bar towards the back of the car?

Just like the title say, I am putting in a triangulated 4 bar in the 36 coupe and it would be less floor cutting to run them out the back. I know it is not ideal, but will I die . The car is a taildragger with bags in the rear only. Not trying to hook up just get about 8 inches of travel.

 

I've seen a dirt track suspension called a Z-link that runs the bar to the rear, I don't see why you can't.

 

It would tilt the rear end yoke up every time it hit a bump. Think about it, the bars travel in an ark, and get shorter as they go up or down. The top bars would pull to the rear, and the bottom bars would pull to the front. Depends on how much the rear end will travel up and down as to whether it would cause a problem.

 

Hey FAW-

I totally understand the issue. I also know people do it and say it is no big deal and yet Air Ride and other people say never do it. I guess I want to know if it is not ideal but do able or OMG you are insane to do it. Also is it a binding issue or a pinion angle issue or both?

 

As long as the intersect point is in the correct place,, it shouldn't be and issue. It wouldn't matter where the bars are as long as they come together at the front U joint. (Roughly)

To achieve this the rear bars would have to run downhill toward the front of the car.

 

Tinman I am not sure I follow, but I am very interested. Any chance you could do a drawing or something?

 

Sure it can be done, and would probably work just fine. How much travel will you have. Most lowered cars without airbags only have about 2 or 3 inches of travel, so it shouldn't be a problem.

 

With 8 inches of travel it would become a pinion issue for sure. As the rear end moves through its arc of travel the rear facing bars are going to pull back on the top of the rearend forcing the pinion to rotate upwards. As FAW said the amount of travel will determine the problems that it will cause but 8 inches seems like a lot for it to work. I would think you are going to get pinion and binding issues. Here is what Air Ride Technologies says on their site

What about "reverse" 4 links? What happens when you run the bars backwards?
NO NO NO!!! By the way, did we say NO?! It doesn't matter what the truck magazines say... DO NOT run the 4 link bars backwards! Here's what happens... When the top bars are run backwards, the diverging arcs of the upper and lower bars will create such a massive pinion angle change that under extreme amounts of suspension travel, you may actually pull the driveshaft out of the transmission! If you want to see this effect for yourself, get a sheet of pegboard and a couple of yardsticks... simulate the scenario for yourself. The second effect of running the upper bars backwards is completely screwed up handling dynamics. With a normal 4 link, when you hit the brakes, the suspension geometry wants to lift the rear of the vehicle... therefore trying to "plant" the rear tires and assisting the braking action. When the upper bars are reversed, this dynamic is eliminated or even reversed... when you hit the brakes the suspension actually unloads the tires thereby massively reducing available braking performance. This is not our opinion... it is simply physics.
We don't know who thought up this "backwards" 4 link stuff but apparently it was originally used to provide clearance for an airspring sitting on top of the lower bars that pointed to the front. The truck magazines picked it up, the readers took it as gospel, and the rest is history.

 

I actually am probably over stating the travel it would be closer to 5 or 6 inches; however I included situations where there is less weight on the rear (cresting a hill) so I added 2 inches.

 

K13 said it. You are fighting engineering mechanics and physics and you will lose. Will you die? No, but just do it right and avoid the troubles you will create with backwards bars, even if only the top two. It just does not make sense.

 

If you don't have room for the upper links, then why not use a trailing arm set-up? You only have the lower links plus a panhard bar.

 

I would just cut the floor then build a new floor over it

 

When the body rolls to one side, when you round a curve, the low side will twist the axle one way and the high side will twist it the other. This bind will stress parts untill the week link is found. Eventually something will break. I've seen this set up fail before.

Craig

 

bad idea. physics will overcome

 

Research the cantilevered suspension being used in air bagged trucks these days. That may be the solution you need. The idea you propose will have excessive pinion variation and could be hard on parts at the very least. It takes quite a bit of planning to get good geometry on a suspension system. Either buy the engineering or enlist the help of someone who knows what they are doing in such situations. Try to PM DBRods here. Jon will be able to get you some good links. He does that stuff professionally.

 

There is a shop here that did a truck that way. I don't know how much travel they actually run it through though. I remember them mentioning they split the pinion angle so it would be correct in the middle ride height (where they almost never run it), and yes it will lay on the ground or clear curbs and speed bumps.

As for how well it works, evidently just good enough to make it to and from the shows, I have never seen it go anywhere else.

 

Lucky,
the best way to see how this package would work is to make popsicle stick models or the suspension and cycle it through its motion. The pinion angle deal is the major issue with this set up and if you are going to have 5" of travle it will not be good.
Another solution would be to make the control arm attachment points on the axle float and control the pinion angle with a torque arm mounted low and long like a late Camaro. That way the control arms will work like a Watts linkage and keep the axle centered in the wheel wells. Again the torque arm would need to be as long as possible as the rear end will now swing in an arc and the pinion angle will change just like it would with ladder bars.

Roo

 

There is a video on the Suedes board that shows this EXACTLY.

http://www.suedescarclub.com/pn/index.php?name=PNphpBB2&file=viewtopic&t=584

 

Alright I have been convinced...A little bit of floor trimming is in my future...

 

Im sorry the linkdidnt work right,

Goto the suedes board, goto the Runing Gear forum, and click on the thread Titled
4 link suspension explanation video

 

I can get to the thread, but I do not see the link to the demo.

 

where on a 36 would you mount them to if the pointed towards the rear? behnd the axle there is only the x-member that holds the bumper...

surely its got to be easier to cut the floor rather than fabricate a new x-member man enough to hold the top links of a 4-bar.

 

Its the top bar on a triangulated setup so they would go to the framerails on either side of the gas tank.

 

In this situation I think I'd look at some rather long "truck arms" and just avoid all the upper arm/link drama. You would just need to engineer a correct panhard bar and that would be it.

 

Heres the reason why :

http://www.youtube.com/watch?v=JHwoGQPHcRI

 

Thanks man that was pretty cool

 

^ yeah thats rad, funny to think a few pieces of cardboard can help you determine so much.

 

Just remember that the video depicts suspension travel that is double the longest link. That exagerates a great deal. The actual suspension travel in a street car is more like 1/4 of the longest link. Short upper links work well in that case. You have to look at pinion angle in the highest and lowest travel. The video shows something like 4 feet of travel, by scale

 

^yeah by scale its huge.

If you run shorter upper bars you will have some pinion change but not alot. Some 60's GM's have the "banana bar" that is a 3rd link thats alot shorter than the 2 trailing arms, and its worked on those cars forever.

 

i have no tech to offer,but got a pic of said vehicle?
here is mine i went with front bar set up.i have a monster notch on mine.13 inches to be exact...