4 Link Suspension Design Question

[Dr. Dave]

I have a 1994 Phantom, it uses a horizontal and parallel 4 link rear suspension with a Watts link. The top links on the birdcages sit about 2" above the axle while the lower links are situated about 5" below the axle. Most 4 links I've seen the links are an equal distance above and below the axle height. Is there an advantage to having the lower link a greater distance away for the axle center? Does it matter? IS it best to have the links as far apart as possible?

The Watts link bell crank is mounted horizontally (the spherical rod ends connect to the bell crank on the same horizontal plane). I've only ever seen them mounted vertically. I'm assuming this was done to get the lowest roll center possible.

I'd be most interested to hear any thoughts or insights you have on the suspension anomalies.

[mcenhillk]

I can't get my head around how a watts link would work with the bell crank inline with the connecting rods. Can you post a picture?

[Dr. Dave]

[mark 21]

The watts link does not care if it is set vertical or horizontal. It main purpose is to keep the axle from going side to side. It also effects the role center of the car. That was the idea for having it horizontal. Look at the KBS/invaders there pan hard bar attaches low in the chassis.The newer Red Devil have watts links that are done in this manner. Some of the older red devil that had watts links had them vertical. But t red devils had pan hard bars on early cars before he used the watts link. The H link is mounted low in the Nova cars also.

[mcenhillk]

Thanks for the picture. That's not at all what I was picturing. I've never seen the link assembly mounted like that but as mark21 said, it's just to prevent side to side motion and this constrains that motion. I might have to consider that for my car.

As to your question about the 4 link. If the links are the same length and parallel, I wouldn't think it would matter where the axel is mounted on the vertical arm. Having the lower arm further from the axel would reduce the compression the arm sees while under braking torque, maybe that's why they designed it that way.

<disclaimer> I'm not an engineer. I haven't stayed at a Holiday Inn Express recently. I may cause cancer in the State of California. </disclaimer>

[cjsmith]

Dave,
A couple of thoughts on the picture. Not sure if the tabs of the bell crank have been pulled in by the bolts holding the rod end but I don't see much room for suspension to travel with out the rod ends binding on the bell crank. Usually there are spacers on either side of the rod end to allow free movement. Second, I don't see a jam nut on the rod end at the bell crank. Over time with out having the threads locked in place that can loosen up the threads and eventually strip out, especially since the rod looks to be aluminum. If you can't get a jam nut on due to room, remove .25" from the shaft.

[Dr. Dave]

Thanks for the comments everyone! Very much appreciate the help/advice! I think I need to fab up a new bell crank and like CJ mentioned make it so that spacers could be placed on each side of the spherical rod ends to give them more up/down freedom. Good know the 4 links ok and I'm free to move the location of the upper link..as long as it stays parallel. Oh and mcenhillk, thanks for the laugh, maybe I need to stay at Holiday Inn,lol.

[jrh3]

Thanks for the comments everyone! Very much appreciate the help/advice! I think I need to fab up a new bell crank and like CJ mentioned make it so that spacers could be placed on each side of the spherical rod ends to give them more up/down freedom. Good know the 4 links ok and I'm free to move the location of the upper link..as long as it stays parallel. Oh and mcenhillk, thanks for the laugh, maybe I need to stay at Holiday Inn,lol.

It would be interesting to know how much suspension travel the car normally uses. 1 1/2"?
The different heights of the bird cages may be insignificant and just designed for convenience. Parallel vs non parallel links - might be some useful/detrimental toe changes. A big piece of butcher paper, yard stick and compass might be enlightening unless you have the appropriate computer program.