Thread: Binding 4-Link

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Im building a parallel 4-link set up and im concerned that in might bind if i build it the way i want to. The bars are going to be about 24" from rod end to rod end, the brackets are going to be mounted under the frame rail and is going to be on air bags, so the top of the brackets can't hang over axle to much or they will hit when air is let out. There is about 8" from the top of the housing and the bags will deflate 4", so i've made the brackets hang lower to the ground and was wondering how far or were the rod end should sit in relation to the top of the axle housing and could there be binding if it gets to close to the axle center line? please any help thanks.

Well, I'm no 4 bar expert, but no one else seems to have jumped in yet, so let me give you some basic thoughts.

My understanding about 4 bars is that you want them to be equal length and parallel to the ground when at ride height. They should also be parallel to each other so that you get the parallelogram (is that a word ?) effect when the rear axle is going up and down. From the way I read your description, are you saying that because of clearance issues your bars are not parallel to each other now?

If you can post a picture or drawing it would help.

By the way, welcome to the forum.


Don

The top bar is a pull bar, it should be an inch or so minimum above the Centerline of the axle. At or below the centerline and it becomes another push bar and you will have no control over your pinion angle and terrible things happen.

Not quite right, Dave, the top bar is always a pull bar(under accelleration) even if it's actually below the axle centerline. What you get is tremendous stress increase due to leverage when the axle is closer to one hinge point,or outside the two points altogether.Any small amount of "give" will be increased with any movement of the axle above or below the exact center, with drastic movement possible with it outside these points.

While 4 bar suspension is nice to look at, there is a chance for potential bind (says I who has a 4 bar rear suspension) take a look at 4 link setups as an alternate.
http://store.gaugemagazine.com/index...ROD&ProdID=176

http://www.afcoracing.com/tech_pages/4link.shtml

Both are good reading - wish I had before buying my chassis

This is a bit off of the original topic but . . .

Also important is the 4-links relation to the cars center of gravity.
The bar angle should converge near the vehicle's center of gravity.
If its too far back = wheelstands = wasted energy.
If its too far forward = inadequate rear wheel loading = tire spin.

Which introduces a curious problem to solve.
Center of balance (vertical axis) is easily found by balancing your car on two jack stands.
How would one find the true center of gravity ie horizontal axis?

I suppose most just use the center of balance at the frame as their reference point.

Bert

I think we're talking parallel 4-bar, not a racing 4-link. Most of the manufacturers don't place the top bar very far above the C/L of the rear axle.

Originally Posted by Henry Rifle

I think we're talking parallel 4-bar, not a racing 4-link. Most of the manufacturers don't place the top bar very far above the C/L of the rear axle.

Makes good reading and since most chassis mfrs offer a version is appropriate. The first link, shown below again, is a street design for air suspension.

http://store.gaugemagazine.com/index...ROD&ProdID=176

Originally Posted by R Pope

Not quite right, Dave, the top bar is always a pull bar(under accelleration) even if it's actually below the axle centerline. What you get is tremendous stress increase due to leverage when the axle is closer to one hinge point,or outside the two points altogether.Any small amount of "give" will be increased with any movement of the axle above or below the exact center, with drastic movement possible with it outside these points.

How is the top bar going to pull if it's on the push side of the axle..??????

JMO, but I really like the triangulated 4 bar for the street, keeps from having to find room for a panhard bar, too.....

I think we're talking parallel 4-bar

Hmmm - didn't realize I was that far off topic -
Thanks for the reality check.

The triangulated version Air4Link™ is a tubular version of the tried and true rear suspension that GM has used since 1964.

Uh oh - confused again - GM used them in what applications.

Bert

I think we're talking parallel 4-bar

Hmmm - didn't realize I was that far off topic -
Thanks for the reality check.

The triangulated version Air4Link™ is a tubular version of the tried and true rear suspension that GM has used since 1964.

Uh oh - confused again - GM used them in what applications.

Bert[/QUOTE]

How is the top bar going to pull if it's on the push side of the axle..??????

Dave,

He's correct. If both were pushing, the axle would have to move, because the 4-bar ends are all that's holding it in place.

Check the diagram. If you torque the axle, it will try to rotate clockwise. It will use the top 4-bar eye as a pivot point, causing a pull, and push on the lower 4-bar eye.

For the axle not to move, the sum of the forces in the 4-bars have to be equal, and in opposite directions.

Of course, none of this means that it's a good setup.

LOL,,,, That set up wouldn't work!!! Guarantee that would be one freaky ride on acceleration..... I guess I put too much empahsis on the competition set up for cars. The triangulated 4 bars are nice on the street, but other then a bit of binding the parallel 4 bar will work ok....

HenryRifle's diagram is basically what a lot of cars already have, except the upper "link" is the leaf spring, the bottom one an add-on traction bar. Agreed it ain't great, but it can work.

Yup, Guess I had to see it in apicture.....