odxr

What year was the design changed?Can the newer version be used on the early c4?I noticed the design was changed to eliminate the camber change during suspension travel.

ex-x-fire

84-87 is the early design.

WVZR-1

I believe it's safe to say that if you had brackets from an '89 or newer that used 12mm mounting hardware they're the latest. To use these on an earlier car you just use the appropriate 12mm hardware, drill the housing & cover. SPO information seems to hint that '88 still used 10mm hardware but the bracket was different. I had never noticed that until you asked your question. I just always thought either 10mm or 12mm hardware.

I've seen your "reason why" debated I believe.

hcbph

Have you compared it to the Banski kit? If you use the newer ones you might be able to sleeve the bolts down to 10 mm and not have to drill and tap anything assuming this other one doesn't do what you need.

Just a thought.

Tom400CFI

Do you mean that the newer design doesn't eliminate camber change? I agree that it doesn't eliminate it. Newer car still exhibits pretty radical camber change throughout it's travel. Only way to eliminate it is to lower the lower arm mounting point until it's the same distance from the u-joint center line (pivot point of the "upper arm") as the outer u-joint centerline is from the outer lower arm/knuckle pivot.

odxr

I have a 57 Chevy I am working on with 85 vette rear suspension.The camber change when cycling the rear suspension is quite severe .I got a set of 1990 brackets and I am going to check the fit on those.I have a buddy that has a 4x4/ fab shop and I just might try making a single piece the bolts across the bottom of the diff for both sides.I have a 87 I want to fix this on too.Tom400cfi spotted the cure for the design.I can't believe GM would design something like that but low profile tires were just coming on the market .

Tom400CFI

I hear that...but keep in mind that there are benefits to that feature in a typical street car. A street car has some body roll in turns. Adding negative camber during jounce (compression) will compensate for the angularity of the body and consequently suspension points and tire angle (actual camber)....keeping the tire straight up and down during cornering and body roll. In theory.

If we eliminate body roll though, with big bars, suspension geometry and low COG, then we want to minimize camber change, since we won't create any with body roll, but we'd be hurting traction through suspension jounce and rebound over bumps as the tire won't stay vertical on the road.

MatthewMiller

This is a really important point. If a suspension has no camber change during compression and rebound (which is kindergarten simple to accomplish, btw), then it will exhibit positive camber gain on the outside tire at the same rate as the car's roll angle. That is a bad thing for grip!

Now we're getting complicated. If you eliminate roll through sway bars, and suspension geometry, you are probably going about it the wrong way. This would be a thread unto itself (huge books have been written on it!). It's arguable whether eliminating all roll is a worthy goal, at least with a passive suspension. But the ideal ways to minimize roll are mainly with high spring rates and low CG. Purpose-built race cars these days are often using a separate heave spring so that they actually have a lot more spring rate in pure vertical motion (heave/dive/squat) that in roll. This is largely due to aerodynamics, but the point is that it's generally not ideal to have a lot more roll rate than heave/dive/squat rate. The thing is, if you use springs and low CG to limit suspension movement, you're also limiting the suspension travel over bumps, squat, and dive. So there is not a need to minimize camber curves in such a setup.

Radial tires are interesting creatures. They actually want to corner with negative camber (tires leaning into the corners). So the idea of keeping a tire perfectly vertical in cornering is not really the goal for radial tires. That said, if you look at good action shots of any production car cornering hard, you won't find any with negative camber on the outside tires. It's a whole lot harder to make that happen than people think. If you don't believe that, here's a pic of my car with 1125lb front spring, 550lb rear spring, -3.5* static front camber, and -2.5* static rear camber:



At best, you see that the front is only just vertical and the rear still has a little positive camber. At some point you have to account for longitudinal traction in braking and acceleration, though. So there are limits to static camber settings.

To the OP's question, I think the basic answer depends on whether the two camber arms (older and newer) at the same length. The newer C4 rear geometry changed more than just the camber arm length. I believe the mounting height for the camber arm was lowered to reduce the roll center height. I don't know what introducing the newer camber arm into an old suspension actually will do. One thing about all these OE arms is that they seem to have a bad habit of moving their static camber setting (the eccentric) when a car is cornered hard. The Banski arms (or any spherical bearing setup) will eliminate that.

Tom400CFI

with all of that. I was just trying to KISS an answer to "I can't believe GM would design something like that".


The pic is great, and pics like that can be great diagnostic/tuning tools. At least, for a poor guy like me.


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odxr

Matt-very cool pick of your car working very hard-left front wheel is off the ground.Probably a little frame twisting going on there.I got a set of the 88 up style brackets from ebay cheap.The mounting point is lower to the ground and I am going to install them on the project car to see if it will work.I had an old 77 Datsun 280z that I ran hpde track days with and it was set up with negative camber front and rear.Its amazing when you get a good set of tires up to operating temp how good they will stick.

MatthewMiller

Yeah, that was the first time I tried Hoosier A7s on the car. They have stupid grip, even compared to my Rival S tires that are legal for CAM-S. Truth be told, I did start to worry about the unibody integrity. But actually, when it can carry the front tire like that it tells you the frame is resisting torsional loads pretty well. The more it twists, the less the tire would come up. The targa top must be seeing some hellacious loads though, because I know how limp the whole car is without it!

What the tire coming up means is that the car is relatively stiff in the front roll rate (spring plus swaybar), and therefore transferring a lot of grip to the outside rear tire. That makes it launch out of corners hard, possibly at the expense of steady-state grip compared to if it had more rear roll stiffness. I will probably experiment with a bigger rear swaybar to see if moving some grip to the front will be an overall improvement. I may find that helps with the Hoosiers but not with the Rivals.

I'm curious what you'll find with the updated camber rod and mount. If the length is correct, it will probably help keep the rear grip more linear, with less jacking effect (due to lower roll center). Let us know.

Tom400CFI

Up to 1000 lbs of force, according to the engineers. That is a serious load.

MatthewMiller

That was presumably with 1980s street tires at 255mm width, though. In that pic I'm running 315 Hoosier A7 tires. Consider that I'm probably pulling 1.4-1.5G in corners. We can probably add 500lb to that number for my situation.

Tom400CFI

Yeah, that is quite possible. I've always thought that the most force applied to the frame in torsion would be driving through a gutter diagonally, like when entering or leaving a gas station. When doing that, I can get my car on two opposing wheels for a second, before it teeters over onto a third wheel (or I roll back onto flatish ground). Anyway, at that point, 50% of ~3400 lbs is twisting the frame. What is going on when you're cornering like in your pic? Hard to say but if you're pulling over 1g (and I have no doubt that you are), with one wheel in the air, it stands to reason that you could be applying 1.xg * .5 * ~3400 lbs in torsion to the frame of the car. She's under some stress, for sure.

Whatever the actual numbers are, the measured figure in the text above was pretty mind blowing when I first read it. The roof has a hell of a job to do!


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odxr

I bought a set of 88-up brackets on ebay.I am building a 57 Chevy with c4 rear suspension I noticed the extreme camber change while cycling the suspension with a floor jack.The 88-up brackets are a direct bolt in.I am sure GM didn't have the software and computer power we have today with programs like Solidworks.

kael

Imagine in your mind going fast around a corner and what the extended wheel is doing. See the contact patch, grasshopper. Left turn, right turn...right turn, left turn.