4-link bind

[JRouche]

Ok guys, here is my issue, prolly has more to do with body roll than the 4-link. I have a art morrison 4 link and I am wrapping up a swap to watts link from pan hard bar. So I have the car jacked up and the body supported. I ran the rear end up and down with the floor jack vertically, checking for binding or clearnce issues, all good. Then with one end of the rear end unsupported and lifting the opposite end to simulate body roll. The rear stayed almost flat with just one end supported. And so its only the weight of the rear end to cause some twist but I would have expected it to twist (droop on the unsupported side) a lil more. Its the 4 link that is keeping it from twisting, yeah, bind.

So I blocked one side away from the frame to keep it from going up and jacked up the other end of the rear end to force it to twist. And before you cringe, I was only giving it light pressure. I made sure to not twist the link bars more than the small amount of bushing material could handle. They still had some squish left in them, I was watching the bushings during the twisting. .

I used a digital protractor to determine the amount of twist I got to, which would be induced by body roll while driving. With a moderate but not too much twist the number was just at 5 degrees of roll.

Now not knowing much in the way of car geometry and body roll I gotta ask, what would be a reasonable amount of body roll for a street car. OK.. WAY open ended question. But some ballpark number would be nice to know. Like something in between a track/street car like many here and a stock setup. I would just like to know if 5 degrees and under is within "standard" parameters.

The car is a 62 nova with a weight around 2800-3000lbs, has the AM 4 link, watts link, ART shockwave air ride, ford 9 inch, splined roll bar rated at 310lbs (I can change that), mustang II front end with shockwaves and a roll bar.

Just trying to get an idea of how much roll 5 degrees is, seems like alot. If I can keep it under that then Im not worried about the bind in the 4 link. I just want to nip this in the bud while I have it still in the build phase. If its too tight I will modify it to become a three link, I would rather not at this point though, I need to drive it after 13 years of building LOL

And it got me thinking. Some bearings at the rod ends would take care of the bind, not that Im going down that road either. But if the ends were allowed to rotate in the bars then there would be another 5 degrees of rotation before the bind was due to the bars themselves. That might be a nice lil bench project in the future though just to see.

So, summary...... Is 5 degrees of body roll well within the "normal" numbers???? I expect it should be, that rear end was pretty well twisted with that much. Looked like at least 4 to 7 inches of displacement from one side to the other.

Any input would be great, help a newbie out!!!! Thanks, JR

[parsonsj]

5* of roll is probably fine. That's a lot of body roll, and for street use, it will work great.

jp

[JRouche]

5* of roll is probably fine. That's a lot of body roll, and for street use, it will work great.

jp

Thanks for the info John. I just really have no clue to where body roll is in degrees on a street car (or track car), just never came up before. Thanks.... JR

[silver69camaro]

It sounds like you have our drag-race four link with poly rod ends. Five degrees is perfectly OK for the street, more handling oriented vehicles are around 2.5 to 4 degrees. Our triangulated 4-bar can rotate 8 degrees w/o bind, 3-link at 16 degrees.

Don't put rod ends in there. You reduce the angular deflection to near zero. The key to getting a four-link to roll is "soft" rod ends, either poly or rubber. In a roll, one link needs to be able to change length, and the urethane/rubber allows that to happen. Also, using sphericals, the jam nuts will loosen under a hard bump and actually pre-load the front end. Bad!

[JRouche]

It sounds like you have our drag-race four link with poly rod ends. Five degrees is perfectly OK for the street, more handling oriented vehicles are around 2.5 to 4 degrees. Our triangulated 4-bar can rotate 8 degrees w/o bind, 3-link at 16 degrees.

Don't put rod ends in there. You reduce the angular deflection to near zero. The key to getting a four-link to roll is "soft" rod ends, either poly or rubber. In a roll, one link needs to be able to change length, and the urethane/rubber allows that to happen. Also, using sphericals, the jam nuts will loosen under a hard bump and actually pre-load the front end. Bad!

Hi Matt, thanks for replying. Yup, you got it, its your poly end 4 link. And I love it, bought it back in 95. Thanks for the info, at 5 degrees it was looking way rotated. So with my semi stiff sway bar and repositioned springs it should be within the 3 degree mark.

Oh, and the bearing thing. I wasnt talking about spherical bearings. Im thinking about bearings that would allow the rod of the ends to rotate within the arms. Thinking of the stiff "roll" of the rubber ends. If there was a roller bearing that allowed the rod to rotate free of the bar. So you still have some give and noise protection with the poly ends but they would rotate freely, independent of the arm. They would have to be strong in the axis (fore and aft), not unlike a double angular needle bearing, they can handle quite a side load. Dunno, just thinking outside the box here. Thanks for the info.. JR

[BillyShope]

Matt didn't mention it, and it looks like you won't be doing it, but I want to comment on your thoughts about converting it to a 3link.

About 15 years ago, Steve Magnante and I were working on what was to be the basis for a "Hot Rod" article. We had a racer who was willing to be the "guinea pig" and I was to provide the setup information. The plan was to remove one link from a 4link and then adjust to provide equal rear tire loading on launch. Our collaborator got his car together and did some driving on the street. I don't think he had more than half a dozen hard launches before there was a failure. Fortunately, no one was hurt and there was a minimum of body work damage.

As an engineer, I blame myself for the problem. If I had done a stress analysis, I would have realized that the failure was unavoidable. I don't know who manufactured the 4link and I'm not saying that your AME 4link would fail, but...as common sense (which I seem to lack) would dictate...when you remove 25% of the links, it's pretty obvious that the remaining links are called upon to do a little extra work.

In short, a 3link should be either purchased or fabbed from scratch, paying little or no attention to the tubing diameter or wall thickness used in the 4link kits.
http://home.earthlink.net/~whshope
over 140,000 page views

[JRouche]

Matt didn't mention it, and it looks like you won't be doing it, but I want to comment on your thoughts about converting it to a 3link.

About 15 years ago, Steve Magnante and I were working on what was to be the basis for a "Hot Rod" article. We had a racer who was willing to be the "guinea pig" and I was to provide the setup information. The plan was to remove one link from a 4link and then adjust to provide equal rear tire loading on launch. Our collaborator got his car together and did some driving on the street. I don't think he had more than half a dozen hard launches before there was a failure. Fortunately, no one was hurt and there was a minimum of body work damage.

As an engineer, I blame myself for the problem. If I had done a stress analysis, I would have realized that the failure was unavoidable. I don't know who manufactured the 4link and I'm not saying that your AME 4link would fail, but...as common sense (which I seem to lack) would dictate...when you remove 25% of the links, it's pretty obvious that the remaining links are called upon to do a little extra work.

In short, a 3link should be either purchased or fabbed from scratch, paying little or no attention to the tubing diameter or wall thickness used in the 4link kits.
http://home.earthlink.net/~whshope (http://home.earthlink.net/%7Ewhshope)
over 140,000 page views

All great info.. If I were to "convert" this 4-link to 3-link I would keep the lower arms and make a top third link, using the same axle brackets, they are stout.

The removing of one upper link from a 4 link does not make 3 link :) Im pretty sure of that. I am not an engineer so I tend to "over build". And it being a street car the extra weight I would unnecessary have is ok. My third link would look more at home in a rock crushing truck LOL An example would be my watts link I just made.

But I am pretty good at copying proven systems and would go that route with some extra spice added :)

But as it is now the 4 link stays. Unless I see the arms unscrewing the rod ends due to bind it will be ok. I really need to stop building and finally drive this pig.

Thanks for the info, Im a sponge for knowledge and know when to listen to my betters, yup ya darn engineers :) JR