Thread: 4 link question?

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Want to build a rear suspension similair to whats shown in the pic. One question I have is: wouldnt this set up be prone to binding? As the rear end moves up in travel wouldnt it want to pull the spring forward as theoretically the radius rods would get shorter? Another question I had: what is my initial setting for the 4 bar? My gut tells me leave one end loose. Set the car on the ground to load the spring and then hook up the 4 bars. Any thoughts appreciated. Im new to this so bear with me.

Well, those four bars you pictured are pretty short, too short IMO. If they were longer they would not pull the spring and axle any more forward than would a hairpin or wishbone rear setup. These rears only tend to travel up and down a few inches at most, so that arc doesn't impart too much pull on the axle. I also don't like the way he positioned the front of the bars way out on those spacers.

The ideal way for four bars to sit is parallel to the ground when sitting at ride height. You want to install them so they sit like that.

Don

This thread may help you understand the geometry involved if you read Billy Shope's links. As far as the setup you've shown, I would agree with Don. The links are too short. I think if I were going to fabricate it according to what is shown, I'd incorporate a large poly bushing between the spring and its mount at the center of the spring so that the spring could roll a little and not bind up the whole mess. But like Don said, with longer links, this would not be any different than any other hairpin or parallel link arrangement and the kink in the system could be tolerated by the spring.
http://www.clubhotrod.com/forums/showthread.php?t=37299

I like your new Avatar, Richard.

Don

Thanks Don, High School study hall, circa 1959. By the way, I don't know if you caught my roadster pic and verbage. I tagged it onto the Jets/Funnys thread.

Do they actually sell a poly bushing for that or would it have to be made?

Richard, I didn't see that, I'll look it up.

Customsleds, yes, companies like Suicide Doors, Pete and Jakes, etc sell various four bar setups with poly bushings. They will make them to any length you want and you can get them even in stainless.

Here is a picture of some we have, we cut these in half to mockup the suspension, then ordered a set of stainless ones in the exact length.

Don

I laid the dimensions out in mastercam and see why the longer rods would help. With the longer rods in 5 inches of travel it only moves forward around
.400 where as with the short rods in 2 inches of travel its .400 of forward movement. I have the stuff bought and most of the frame work is done so im gonna assemble it and see what happens. The spring in the back isnt that heavy duty so im sure ill get some flex out of that. I am almost thinking if I could set up something that lets the spring move forward as it moves up. Ill have to look at that. Oh well I guess we will see how good my welds are! Thanks guys!

Maybe this would work maybe not but what if I instaed of the (4) bars Iused
(4) gas shocks? Im tied in good side to side and front to back with just the leafspring so to me the (4) bars are kind of a token anyway. Any thoughts?

You aren't serious, are you? Gas shocks instead of four bars? I think you should post some pictures of this car you are building so we can advise you before you get way in over your head. There are certain things that have to be done to insure a good, safe car, and you seem to be skirting those methods.

Don

Since you have shackles on the axle, it isn't fixed either side to side, front to back, or against roll. Gas shocks won't help that at all. If you went to the gas shocks, the first time you hit the gas hard, the pinion would probably rotate up, bottom the shocks, and probably break or bend the rear spring.

In fact, if you have shackles on both sides of the axle, your rear spring won't prevent side to side movement either.