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LCA Information Guide

Iíll try to explain the function of a rear lower control arm on a 4th generation f-body. Then Iíll discuss various types. Choosing the correct control arm design depends on what purpose youíre setting up your suspension for. First, a little background on LCAs functionality. When a car corners it leans. Sway bars and springs oppose that lean to keep it level. That lean is also opposed by the LCAs. OEM design is open-ended, which allows the control arm to twist. It also uses rubber bushings that compress and give. This is desired for optimal traction. I will explain later. The downfall is that they also allow quite a bit of fore/aft deflection due to this rubber bushings and stamped design. They were not designed to oppose that motion. This is what your springs, shocks and torque arm are for.

Poly bushings are a popular option to rubber bushings. They will deform under pressure and stay deformed. It is not as elastic as rubber. This means that you might need to replace your poly bushings.

Poly bushings and tubular design control arms eliminate most of the fore/aft deflection, but they will resist the torsion movement with a much larger force. This is called bind. In drag racing, bind is not that big of a factor. In road racing, it is a huge factor. When cornering, a control arm bushing has to give to a certain degree then the whole arm has to twist. Try to visualize this. You have 3 matches, one being the axle and the other 2 the control arms. Glue them together to form a ĎUí. When cornering the car will have centripetal acceleration. The body will lean towards the center of the curve. High-speed turns are banked to minimize that. This is what is happening in the rear. Outside body is higher then inside while axle is still straight. The body also wants to accelerate towards the inside. LCAs are connected to the axle. Try to lift one end of the match up and tilt it towards the middle. If it canít twist youíll break the joint before that happens. Now understand the force thatís trying to do that to your LCA brackets if the LCA wonít twist. The LCA bracket is relatively strong so it will in turn apply that force to the axle. The axle will not give either so it will take the wheels with it. This will force the inside of the inner wheel and outside of the outer wheel off the ground. Iím sure you can imagine what happens next.

Best solution is to get a tubular LCA with rod ends or at least a rod/poly one. This will allow for a great amount of bind free twist. Rods arenít for everyone. They are more expensive then poly bushings. Cheap rods will make noise. Itís your preference on how much you want to spend to have noise free, great handling car. Rods need to be replaced every 2-3 years if the car is a daily driver. They will last longer if you take care of them. Try using a brake cleaner and DGF 123.

Another option is boxing the stockers. If you box the OEM LCA, you will add additional resistance to twist (i.e. more bind) and you will not add resistance to fore/aft motion since the bushing will still be the weakest point. So you wonít help the performance in drag racing and hurt the road racing capability of the car. In other words, donít do it.

1LE LCA (GM p/n 10164151) are good for all around performance over stock. They are the same as stock, but have higher durometer rubber bushings. Itís basically stiffer bushing that limits the fore/aft motion, but still allows for deflection unlike tubular and boxed designs. 1LE LCA are about $50 each. Do not buy used ones, since rubber deteriorates. Until I find someone with old 1LE controls arms I honestly couldnít say how long they last. Weather factors can also speed up the process. Have you ever seen cracks on brand new tires? They have been sitting too long and were kept in improper conditions. Humidity and dry heat will speed up deterioration of rubber.

Donít trust the descriptions of the LCA on the various vendor websites. They plain out lie. Do you think theyíd rather inform you or make money? Iíve seen descriptions like ďimproved handlingĒ and ďcompletely outperform the weak, factory, stamped metal arms and soft OEM rubber bushings.Ē You couldnít get a more general statement then that. Improve handling? Not on this planet. Outperform in what? Iím sure they just forgot to mention that. I did notice that a lot of them include some words about bind. But only after that fact blew up in their face. I doubt they would have edited anything if not for more informed customers. I would stay away from poly period, unless you plan on grandma driving your f-body through the turns.

Remember, ďdrag race onlyĒ, when buying those tubular or boxed poly/poly LCA.

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