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My '72 Supreme has the rear boxed LCAs mounted at a lower point on the rear axle. I know this helps with traction off the line, but can somebody please explain to me (in a simple way) how?
I think it has more to do with the angle of the arms than what hole it is on. More holes mean more adjustability for tire size changes and spring changes. It should be in the hole if done right because that's the right angle for the arm with the combo the car has. The idea is to drop weight on the tire and keep it there so it plants and gets traction, but doesn't rebound off after the initial hit.
The instant center is the imaginary intersection of the centerlines of the upper and lower control arms. Unlike a ladder bar suspension, the location of the instant center changes as you articulate the suspension. This matters because the location of the IC relative to the car's center of gravity affects the load on the tires when you accelerate and it changes as the suspension squats.
Actually, the arms are boxed for stiffness, not strength. Yeah, there is a little more strength from the added material, but the real problem is stiffness. The factory U-shaped stamped arms spread under load (the legs of the "U" deflect relative to one another) which causes the LCA to have axial compliance. This causes all kinds of monkey motion in the suspension, which is never a good thing for traction. A box is substantially stiffer than a channel, which allows better control over the axle location.
Actually, the arms are boxed for stiffness, not strength. Yeah, there is a little more strength from the added material, but the real problem is stiffness. The factory U-shaped stamped arms spread under load (the legs of the "U" deflect relative to one another) which causes the LCA to have axial compliance. This causes all kinds of monkey motion in the suspension, which is never a good thing for traction. A box is substantially stiffer than a channel, which allows better control over the axle location.
Actually, the arms are boxed for stiffness, not strength. Yeah, there is a little more strength from the added material, but the real problem is stiffness. The factory U-shaped stamped arms spread under load (the legs of the "U" deflect relative to one another) which causes the LCA to have axial compliance. This causes all kinds of monkey motion in the suspension, which is never a good thing for traction. A box is substantially stiffer than a channel, which allows better control over the axle location.
Yes, and a boxed links with poly bushings do nothing but bind in a g.m. 4 link set up.
or break the mounting brackets on the frame because of lack of "give" . Boxed links and ploy bushings in a triangulated 4 link suspension with g.m. tolerance stack. just cause the works to bind, and most when upgrading do this.
Yes, and a boxed links with poly bushings do nothing but bind in a g.m. 4 link set up.
or break the mounting brackets on the frame because of lack of "give" . Boxed links and ploy bushings in a triangulated 4 link suspension with g.m. tolerance stack. just cause the works to bind, and most when upgrading do this.
Which is why whenever poly bushing come up, I suggest using the metal monoball fittings at the front of the upper control arms.
Yes, and a boxed links with poly bushings do nothing but bind in a g.m. 4 link set up.
or break the mounting brackets on the frame because of lack of "give" . Boxed links and ploy bushings in a triangulated 4 link suspension with g.m. tolerance stack. just cause the works to bind, and most when upgrading do this.
Ladder bars and traction bars on a 4 link suspension is another huge waste of time. All they do is bind things up because the suspension has to cycle thru another pair of links, with a different arc. Slapper bars are worthless on these cars because the rearend can’t twist on the arms
Yes, and a boxed links with poly bushings do nothing but bind in a g.m. 4 link set up.
or break the mounting brackets on the frame because of lack of "give" . Boxed links and ploy bushings in a triangulated 4 link suspension with g.m. tolerance stack. just cause the works to bind, and most when upgrading do this.
The lower bars are almost parallel, so bind on polys isn't an issue. Yes, the uppers will bind.. I just put UMI RotoJoints in the housing; the bars have Heims on the frame side.
The lower bars are almost parallel, so bind on polys isn't an issue. Yes, the uppers will bind.. I just put UMI RotoJoints in the housing; the bars have Heims on the frame side.
Yes and no. but these after market links should not be sold with poly at both ends.
People that don't know better thinking they are doing an upgrade, that buy the uppers and lowers, that "most times" have poly at both ends.
Then wonder why the car snapped out from under them, and landed in a ditch. or why they broke a mounting bracket off, or broke an axle because the axle tramped HARD
That's why I put those big *** washers on trying to spread the load.
The washers do nothing against tear out loads. The only load in the UCA is axial, in line with the tube. If the load in the UCA is in tension (which it is when you're accelerating and the rear end is trying to rotate the pinion up), the bolt imposes a tear out load on the flange. The closer the bolt is to the edge, the easier it is to tear out.
The hole should be in the center of the red flange or close to it. Either those are the wrong ears, or the arm is too short. Also, there shouldn't be a gap between the ears to the diff bush. Ideally, it'd be shoulder bolt head, washer, ear, bronze bushing, diff, bronze bushing, ear, washer, and ideally the shoulder bolt would be just ever so slightly longer than that stackup, to allow movement without slop, then jam nuts on the threads of the bolt. There may be customs for control arms I'm missing, but that's how I'd build a machine with that joint.
The hole should be in the center of the red flange or close to it.
The hole should be far enough in from the edge to provide adequate tearout shear area. That may or may not need to be in the center of the flange. Frankly that big square flange is just ballast - much of it serves no purpose other than to be cheap to make.
That is how UMI arms are made:
Factory upper arms don't have a centered bolt hole either, if they did, the inside of the arm would hit the rear end casting. The reason flemming442's arms look like they have so much clearance is because it is a custom 9 inch housing with rotojoints.
Well, all I can say is that those aftermarket arms are substantially heavier than they need to be. The thickness of the ears on the housing end of the arm is driven by lateral stiffness because they didn't want to close out the top the way the factory arms are. Because they're so thick, tearout is not a concern. The problem then is that the small diameter adjuster section is less stiff than it could be for the same weigh. This is a cheap to manufacture design, not a weight efficient one.
Hard to see in the pics but the top of the arms are boxed, just not to the very back like a factory arm. Unlike flemming442's arms, mine are non adjustable.
The hole should be far enough in from the edge to provide adequate tearout shear area. That may or may not need to be in the center of the flange. Frankly that big square flange is just ballast - much of it serves no purpose other than to be cheap to make.
