Control Arm Material Sizing

[CTX-SLPR]

Howdy,

Working on designing some new rear lower control arms for my '64 Riviera because the aftermarket doesn't have any support for this platform. One of the things is that to free up space I'm putting coil overs on it that replace the stock springs that act directly on the control arms. Arms are 26in long and the springs mount at 18in from the front pivot point. The car weighs ~4000lbs wet, but no passengers or gear.

To fit a coilover with enough travel I need to mount the lower mount inside of the square arm, this pretty much means it's going to be single adjustable anyway so I'm going with a Del-Alum (if I can get one that fits) on the frame side and a Johnny Joint on the rear axle. I was thinking 2in square tubing but what wall thickness, 0.120in or 0.250in? Since I'm going to cut a rectangular hole in the top side of the arm for the shock eye (bearing style) to stick down into the inside of the arm, would I need to fish plate the open section even on the heavy wall tubing?

Thanks,

[andrewb70]

Howdy,

Working on designing some new rear lower control arms for my '64 Riviera because the aftermarket doesn't have any support for this platform. One of the things is that to free up space I'm putting coil overs on it that replace the stock springs that act directly on the control arms. Arms are 26in long and the springs mount at 18in from the front pivot point. The car weighs ~4000lbs wet, but no passengers or gear.

To fit a coilover with enough travel I need to mount the lower mount inside of the square arm, this pretty much means it's going to be single adjustable anyway so I'm going with a Del-Alum (if I can get one that fits) on the frame side and a Johnny Joint on the rear axle. I was thinking 2in square tubing but what wall thickness, 0.120in or 0.250in? Since I'm going to cut a rectangular hole in the top side of the arm for the shock eye (bearing style) to stick down into the inside of the arm, would I need to fish plate the open section even on the heavy wall tubing?

Thanks,

I can't help with your actual question, but I never really liked the idea of having extended pocket in the arms to gain shock length. I really like how Global West does it for the a-bodies:

http://www.globalwest.net/64-72-chevelle-a-body-suspension-packages.html

Perhaps you can make something similar or maybe even use that kit if the control arm mounting spacing is the same.

Andrew

[CTX-SLPR]

These are for the rear arms and the top spring mount is barely enough away from the body to get your hand in there to put the nut on the upper spring keeper mount as it is. My only direction to go for a longer shock (the ones I've picked have 4.25in of stroke which is near 7in of wheel travel) is down on the arm. Making a salmon belly arm is not really a direction that I'm interested in going down though I guess it's a possibility. Mounting them on top of the arm would raise my ride height 1in from where I want it and I'd have to extend the bumpstop down to match.

Why may I ask do you not like pocketing a bearing mount shock inside of the square tube arm?

[APinSoFla]

What is a salmon belly arm?

[CTX-SLPR]

One with a bow in it so I could mount the lower shock mount above the tubing instead of inside of it. I think a J-Arm might be another name for it via a quick google image search.

https://static1.pt-content.com/images/pt/2015/02/erygabe6_zps10547d6a-1.jpg
Like the lower control arms in that photo though maybe tubular with the shock mounted in the gusset across the bend.

[andrewb70]

These are for the rear arms and the top spring mount is barely enough away from the body to get your hand in there to put the nut on the upper spring keeper mount as it is. My only direction to go for a longer shock (the ones I've picked have 4.25in of stroke which is near 7in of wheel travel) is down on the arm. Making a salmon belly arm is not really a direction that I'm interested in going down though I guess it's a possibility. Mounting them on top of the arm would raise my ride height 1in from where I want it and I'd have to extend the bumpstop down to match.

Why may I ask do you not like pocketing a bearing mount shock inside of the square tube arm?

The arms that I have seen that used a lower shock or spring mount seems to loose some ground clearance in that are. Maybe it's just an illusion, since I don't have any first hand experience. Extending the top mount just seems like a better idea. Again, this is just off the cuff thinking.

Andrew

[CTX-SLPR]

The arms that I have seen that used a lower shock or spring mount seems to loose some ground clearance in that are. Maybe it's just an illusion, since I don't have any first hand experience. Extending the top mount just seems like a better idea. Again, this is just off the cuff thinking.

AndrewSounds like you are thinking the triangular extensions on the front lower control arms I've seen to extend shock length. In this case, the "salmon belly" arm would cause the same loss of ground clearance that you are afraid of. I'll diagram up the design I have in mind both for you and anyone else who is wondering what I'm doing. Certainly germain for the discussion of material selection.

[dontlifttoshift]

Where is the shock mounted now? That's where I would put the coil over......what ever it took.

I wouldn't use the DelAlum in any solid rear axle control arm, it only allows rotation on one axis, no bueno for a rear control arm. Picture one wheel bumps. Even with the johnny joints the essentially solid bushing will bind and something will give, likely the factory brackets that were designed for a giant, compliant rubber bushing.

[CTX-SLPR]

Rear shocks are mounted behind the axle angled ~20º from vertical around 2in from the brake backing plate. I can't put coilovers back there as there would be no room to put the exhaust between the spring and the tire. Even conventional shocks I had rubbing on the shock or the tires with 3in round tube. With "3in" oval tube I can sneak it through without it hitting anything on the current 225/75R15 tires, 245/45R18's aren't going to give me that room.

Point taken about the Del-Alum, however does that require me to go straight to a bearing mounted coilover on the LCA so the arm won't rotate and spit the spring out? I was seriously considering making this a stepwise improvement by building a spring mount that bolted to the coilover position with 'L' brackets off the bottom of a flat plate. I'm not sure that even with a stock hold down it wouldn't spit the spring out.

Here's the diagram, roughly to scale.
109119

[dontlifttoshift]

Went looking for a picture and found this thread http://forums.aaca.org/f177/dual-exhaust-air-ride-330770.html

You were already there. I forgot about x frame and the steep angle that the LCAs run at. I would be reluctant to box that lower control arm and stiffen up the bushings, pick one or the other. Not unlike a truck arm, those lowers need to twist. Heims solve that, but you can't carry the spring on bar with heims at at both ends. Me personally, I would just replace the factory rubber in the LCAs, have a set of springs made to accommodate ride height and rate, and concentrate my efforts on the upper control arm and the panhard bar.

You may have mentioned it elsewhere, but why the need for coilovers? Coilovers usually solve packaging problems, if it is creating them, it may not be worth it.

If I had to have coilovers, and wanted to fab new control arms, and there was no way to make them work behind the axle, then it looks like you could mount them in front of the axle, inboard of the control arm.

[CTX-SLPR]

Went looking for a picture and found this thread http://forums.aaca.org/f177/dual-exhaust-air-ride-330770.html

You were already there. I forgot about x frame and the steep angle that the LCAs run at. I would be reluctant to box that lower control arm and stiffen up the bushings, pick one or the other. Not unlike a truck arm, those lowers need to twist. Heims solve that, but you can't carry the spring on bar with heims at at both ends. Me personally, I would just replace the factory rubber in the LCAs, have a set of springs made to accommodate ride height and rate, and concentrate my efforts on the upper control arm and the panhard bar.

You may have mentioned it elsewhere, but why the need for coilovers? Coilovers usually solve packaging problems, if it is creating them, it may not be worth it.

If I had to have coilovers, and wanted to fab new control arms, and there was no way to make them work behind the axle, then it looks like you could mount them in front of the axle, inboard of the control arm.What I'm after is freeing up the suspension while getting away from the no longer available rubber bushings for the LCA's. The bushings are "available" but are Caddy pieces with a spacers welded onto the end to make them wide enough, not really want I want. Coilovers are there more to keep the springs in the same spot and get the shocks out of the way. I probably would be able to massage the exhaust to clear the tires and conventional shocks but getting an adjustable rear shock that long enough is also an issue. The springs on the car are overchopped and put me 1in lower than I want and instead of playing around with big springs that I might not get the rate right on then have to have custom ones built again, I was hoping to use "universal" coil over springs to do it.

You mentioned that you the LCA can't carry the spring if it's double heimed, does that apply if the coil over had a heim on it as well? Skipping the intermediate step of the existing springs and going straight for rear coilovers is an option, just a more expensive one.

Thanks

[dontlifttoshift]

Yeah, even with a bearing on the coilover a double heimed LCA won't work with the C/O mounted to it. There is nothing to keep it centered, as in the control arm can flop side to side, rotating on the ball. Then the bearing on the coilover binds and will likely wear very quickly.

[andrewb70]

Now that I see what you are talking about, I get it...LOL

With respect to the lower rear control arms. Take a look at Global west and how they engineer their rear lower arms for the A-bodies. They use a spherical bearing on the frame side and a delrin bushing on the rear end side. This is the set-up I've had in my car for a decade. The logic there is that the spherical bushing allows the rear end to articulate, while the delrin bushing takes some of the lateral load off the upper arms.

If you were to do the same thing, the delrin bushing on the rear end side would keep the arms from rotating and causing problems with the shock bushing.

Andrew

[dontlifttoshift]

Abody LCAs don't run at nearly the angle that the Riviera LCAs do.

[andrewb70]

Abody LCAs don't run at nearly the angle that the Riviera LCAs do.

So because of that severe angle delrin bushing can't be use on the rear end side? Binding issues?

Andrew

[CTX-SLPR]

Yeah, even with a bearing on the coilover a double heimed LCA won't work with the C/O mounted to it. There is nothing to keep it centered, as in the control arm can flop side to side, rotating on the ball. Then the bearing on the coilover binds and will likely wear very quickly.While I could put limiters on the rotation of the bearings, a double heimed arm with a poly bushing on the coilover sounds like it might address the angularity while keeping the arm from rotating on the heims to the limit and wearing out the bearing on the coilover. The arm would be free to stay static rotationally (within reason), the top bearing mount on the coilover would let it move through the angles in both the X and Y planes with the arm, and the double Johnny Joints would allow it to move laterally.

Thoughts?

[dontlifttoshift]

So because of that severe angle delrin bushing can't be use on the rear end side? Binding issues?

Andrew

Yes. The arms are at an angle so as the travel they will swing through an arc (front view)....they would swing like this ( ) if the bushing can't absorb that the brackets will.....for a while. The arc is minimal and well within the range of rubber compliance.


While I could put limiters on the rotation of the bearings, a double heimed arm with a poly bushing on the coilover sounds like it might address the angularity while keeping the arm from rotating on the heims to the limit and wearing out the bearing on the coilover. The arm would be free to stay static rotationally (within reason), the top bearing mount on the coilover would let it move through the angles in both the X and Y planes with the arm, and the double Johnny Joints would allow it to move laterally.

Thoughts?

In theory, that works. I would still find another place to put the coil over.

[CTX-SLPR]

Ok, been doing some thinking on this since I have a nice 40min train ride twice a day as a commute.

First off, the twisting of the arm is not a loaded twisting in the sense that there is a force trying to rotate the arm constantly. In my mind the arm twists because there is a rotational component to it with the () arc travel of the LCA and the spherical bearings have a "stiction" that makes the arm rotate since it doesn't have anything trying to hold it stationary. With this in my mind, having a lower bearing on the coilover shouldn't bind and wear out since they are not loaded in rotation, merely traveling that way since the suspension does move in that direction.

The COM-8 bearing on the Varishocks (chosen because they have a 4.25in stroke), can take 9.5º of angle, less than the Johnny Joints but still they aren't being loaded but I would have to be careful with bumpers or something to keep from the rotation (however lightly forced from the stiction) from riding the bearings on the extremes through the bearing's own rotation around its own axis. This should be easy to do with simply some bailing wire or similar between the bottom coil and the arm as rotation limiters or Teflon sliders on the lips of the opening in the arm.

That failing, the stock location is probably viable if I moved the shock mount on the axle 2in towards the center. This would keep the upper bearing on the stock bolt within it's angle specs and free up enough space to fit the exhaust and the tire. It would need an extended upper mount to keep the spring out of the frame. However, I'd still need a coilover that has something close to the following specs per my calculations: 16in Compressed, 19.7in Ride, 22.5in Extended, and a 6.5in stroke. That's longer than the both Ridetech and Varishock units give.

[dontlifttoshift]

6.9 stroke 13.125 compressed 20.025 extended from ridetech.

RideTech part number 90002075 is different end mount that is 2" taller than the "stock" one which should bring your numbers to 15.125 comp and 22.025 extended. If you really need that extra 1/2", you are making a new lower mount anyhow.

I really think that is the best plan.