Fabricated LCA's

[wellis77]

I'm getting ready to build my new LCA's and will be using a bushed rod end and adjusting camber with the LCA. I am curious about using a direct threaded DOM tube vs. a tube adaptor with DOM tube. Is a tube adaptor necessary/preferred or can I use direct threaded DOM without worry of strength issues? Thanks.

[Motorcitydak]

Typically if you thread DOM tube, you use a thicker wall. Maybe use .250 wall instead of .120. You do that because if you taped .120, there would not be much material left where the threads are which would make it thinner, weaker and more prone to fail. You can correct that by using the thicker wall material but then you have excess weight that you don't actually need. Also, there is the point where the threads stop. That will be a weak point in the tube and it will be prone to fail in that spot.

The better way to do it is to use tubing adapters welded into the tube.

You can also use swedged tube. That is where a piece of tube is smashed on the ends to reduce the diameter in more of a gradual slope. The inside ends are then threaded to accept the rod end

[wellis77]

Thanks Steve. I hadn't considered the point of the threads stopping being a weak point. I've seen direct threaded tube used for rear links but wasn't sure about front LCA's. I will likely run the adapters and call it good.

If I can find a place to bend the tube (I don't have a die this small), I will have the tube bent just after the adapter. If I can't find a place to bend it, how weak of a point would it be if I were to miter a joint just after the adapter and TIG the joint? I've seen it done on some arms, just not sure about the level of strength that would come from that.

[Motorcitydak]

I had to miter cut the track bar for my truck which is built for off road so it sees a fair amount of force. I used 1.5 OD 0.250 DOM and I just braced every cut with more 1/4 plate. I wish I could tell you how much strength was gained/lost doing that but I honestly have no idea. All I know is that it has not failed.

Where exactly is this miter/bend going to be on the arm? Frame side or knuckle side? Are you sure that you really need the arm to be bent? You can rely on the rod end with high misalignment spacers to give you a lot of movement. You can also build the mounting bracket differently to allow a straight arm. Also, will your shock be attached to this piece? I only ask because if you use a bend arm with a shock on top of that arm, it will rotate and put your coil over mount as low as it can until something binds up to stop it like the coilover bushing. That would only happen if you where not using some type of strut rod to hold it in place

[wellis77]

The design of my LCA is very simple, in fact the Viper LCA's are identical from side to side, just two sets of holes to align the shock. The B.J. will be centered between the bushed rod ends so each tube would have the same bend coming from the ends to the B.J. sleeve. Possibly the most literal "A" shape imaginable. I'm going to use a cross-tube for bracing but will also use that cross-tube to connect the coil-over mounts to, not too dissimilar from what I've seen on some RideTech control arms. Maybe hard to imagine but I don't have the design with me. So long story short, the miter/bend will be on the frame side. I'm going to be using bushed ends to eliminate some of the road harshness & vibration, this will be a daily driver after all, otherwise I wouldn't worry about it and would get some highly articulating rod ends, J.J.'s or whatever.

Here is a pic of some fabbed Viper arms along the lines of what I'm planning, but not exactly like this.
https://static1.pt-content.com/images/noimg.gif

[monteboy84]

You're using rubber bushing ends?

If your geometry is correct, spherical joints such as JJ's or heims will ride better than rubber or poly ends, because they allow the suspension to move and work, rather than transmitting everything to the chassis. Del-Spheres get my vote.

-matt

[wellis77]

Planning rubber bushings because poly's squeak more often than not and JJ's or heims transmit loads of NVH. Does the articulation of a Del-Spere really make that much of a difference on front lower A-arms? From the Spohn website, "The delrin bushing cups absorb shock and road noise so you get the quiet and smooth ride of a bushing." I haven't read much about people using these for street cars nor on front suspension so I'm curious how they are on the street. Any experience yourself Matt? The price is good and not too much more for a quality bushing so if the street compliance is good that could be the way to go.

[monteboy84]

Sorry, no experience of my own yet, regurgitating information on this one. I'm planning to go with Del-spheres for the rear and greaseable steel fronts, unfortunately due to winter here I won't be able to report results until May or so.

-matt

[Motorcitydak]

In that case I would see if the del spheres offered enough misalignment to run a straight tube in the control arm and use a mounting bolt that runs parallel to the from. Either that or still use the straight tube in the arm and align the mounting bracket to that. Just make sure that it is aligned with the front mount so you have bind free travel. Doing that depends on what you use for a front mount. If you use a bushing of some sort, you just draw a line (imaginary) thru bolt mounting holes of the front mount and it must pass thru the center of the rear del sphere