Why You Don't Box Rear Upper Control Arms

[Clone TIE Pilot]

Factory rear sway bars do cause binding, they are very poorly designed which is why the aftermarket frame mounted rear sway bars are so much better. There is even a video of a T-type snapping it's rear sway bar. The rear LCAs are designed to flex, when you box them it puts more stress on the LCA frame mounts since they have to twist because the arms can't.

 

[liquidh8]

I have run boxed factory upper and lower control arms on my 79 Malibu Wagon for 40K miles, 100+ a day, of street driving in PA pothole ridden streets. I used Moog replacement bushings on the top, the "1LE" on the bottom. AFCO coils front and rear, AFCO adjustable spring cups, and Bilstein shocks. 17" wheels. I raced it at ATCO, and sprayed the crap out of it weekly.

My personal vehicle had no problems whatsoever. It didn't bounce side to side, tracked strait, turned flat, etc. This is my personnel first hand experience. Is it optimal, no. The uppers should be able to flex and the like, since they are used to locate the rear center, and have to articulate through the suspension travel. There is no panhard bar of watts link to do that job or centering the housing. I did these before really putting much thought in it.

My 65 El Camino is a factory air, 327 4 speed car, and came from the factory with boxed lowers, so I followed suit and figured I would do the top too. Since all the aftermarket makes these boxed uppers and I am handy, may as well have made my own.

Then you start hearing the problems of bind, not running the poly bushings because of bind, etc. But only from the guys who turn. 😀 😀

Face it, most of these boards we are part of, have the members worrying about going fast in a strait line, so everyone wants these strong arms that lock the rear in plate so they car run the max size tire without rubbing during launch. Me, I have a drag car, the wagon will be a DD with track days and autox. Enter the rotojoints, they are great to put in the housing ears to allow one to run a stronger arm, but get the needed differential movement without bind. I will be running these in the BOP wagon, at 120 a pair they aren't cheap, but offer the best option for a car the does more than go strait and park in car shows.

This is just my observations, experience and opinion

 

[joesregalproject]

Factory rear sway bars do cause binding, they are very poorly designed which is why the aftermarket frame mounted rear sway bars are so much better. There is even a video of a T-type snapping it's rear sway bar. The rear LCAs are designed to flex, when you box them it puts more stress on the LCA frame mounts since they have to twist because the arms can't.

I agree. While boxed LCAs or LCAs with a sway bar probably put very minimal stress on the frame that is probably not noticeable under normal driving conditions, they still do put some stress on the frame. I believe the best rear suspension set up you can probably do would be tubular upper and lower control arms with roto joints and a frame mounted sway bar. Just my personal opinion.

 

[jphillips]

So i bought a set of south side uppers and i already have boxed lowers. So my axle is going to bind?

 

[pontiacgp]

Factory rear sway bars do cause binding, they are very poorly designed which is why the aftermarket frame mounted rear sway bars are so much better. There is even a video of a T-type snapping it's rear sway bar. The rear LCAs are designed to flex, when you box them it puts more stress on the LCA frame mounts since they have to twist because the arms can't.

I agree the sway bar does cause a bind but it was an easy way for GM to improve the cornering while using spring rates which gave a comfortable ride. I have the F body sway bar in my GP

 

[liquidh8]

I am running a blazer rear bar like an f-body, in mine now.

 

[Fastmax32168]

I used tubular uppers in my wagon and used the poly bushing that came on the body side, but left the rubber bushing on the rearend side. I have not noticed any issues with the action of the rear suspension since the install. It definitely solved the moving side to side problem however and my nearly too big tires no longer hit the frame when cornering.
Roy

 

[pontiacgp]

The rubber bushing will not deflect enough to compensate for the bind. If there is an empty lot near you take you car for a ride and take some high speed cornering and you'll feel the back of the car snap on you and you'll have lots of oversteer. If you don't have a lot then remove your rear shocks and springs and see how far you can lift one back wheel before the control arm binds it. The engineers at GM designed the uppers to twist to compensate for the bind. If you want to change that set up to a tubular or boxed then you have to replace the set up with something that will compensate for the bind. You need a spherical joint or a roto joint on one end.

 

[jociha]

This is a very interesting subject. It seems to me that when it comes to lower control arms they won't bind because they are almost straight with the car and more importantly they are long so any bind is spread out along the length. We all know lower control arms take most of the punishment because on acceleration the entire force of moving the car is pushing on them, that is why they get boxed, or they will bend. Upper control arms are actually being pulled on so all they could do is stretch, however they do twist a lot because they are more angled to the car and are short. So, if as you say drive fast in a parking lot and you will feel it jerking, then why do factory four link cars seem to do better than leaf spring cars at round track racing? If you install a swivel joint of some kind at one end of the uppers will the car feel loose? So on a typical four link car like all our G bodys, what would be the perfect set up for a street driven car with what most of us like, 400-500 HP?

 

[pontiacgp]

we ran the G body at a 1/3 mile track and there was quite a few other G bodies and they did well on that track. When we went to a 1/2 mile track the 4 link suspension didn't do well with the extra speed going into the corners. The camaro/firebirds with the leaf suspension was a better set up for the higher speeds. One of the problems with a 4 link suspension is the back axle will rotate and rear steer the back end to the left which is the wrong way when turning left. The is no way to correct that condition so you need to turn a 4 link into a 3 link with a panhard bar so there is no accumulated rear steer. With a leaf suspension there are adjusting blocks to give you rear steer turning the rear to the right.