I am finely getting back to designing my 6 link system.

This is my design criteria for now.

1) Control the caster/camber curve better than stock, but still have some camber gain as the suspension loads during cornering. The amount of gain can be controlled by the position on the top link. I need help to determine the amount of gain that I should be looking to achieve. If I start at .5 deg how much should I have with 2” of travel?

2) try to keep the links as long as possible to minimize the amount of toe change. I know that the toe will change with a 6 link setup.

3) For now I am trying to modify and reuse the original strut rod bracket just drilling it for a 5/8” bolt.



I need some help to determine what the ride height should be. I have scene numbers of 17 and 17.5 inches but I don’t know what is being measured. The numbers also don’t help me because my car has the whole rear end removed. I am purchasing the longer spring bolts and I plan on lowering the car from the stock position.



Can someone who has set their car to the proper ride height please give me some feed back. Please check the dimensions that I have and let me know if I am close. The easiest dimension will be the 7.9” from the floor to the bottom of the strut rod bracket.

Next question, under heavy acceleration or heavy corning, how much will the suspension travel? I am trying to determine an expectable amount of travel of the side yokes. Because I am trying to maintain the original strut rod bracket I am getting a large amount of yoke travel, but most during the last 3 inches of rebound. I think that you would only see this when jacking the car off the ground.

I also started in the garage. Here are some pictures of my trailing arm. I’ve added some strengthening ribs to the top bump stop plate. I plan on bolting the top link connecting plate to the bump stop plate.

Mark.

 

For ride height I set mine up by using a magnetic level. I try to set the rearend up so the 1/2 shafts are parallel to the ground.
The lower strut bracket is ok if you add about 11/2 inch tabs to the 4 corners lowering the lower strut rod until again it is parallel to the ground.
For the upper rod the inner mount must be lined up with the lower inner strut mount, the yoke and the inner upper mount.
All 3 have critical lignment.
The upper strut rod wants to be 13.5 inches c to c of the rod ends and the appropriate bracket added to the trailing arm to accomodate this.

 

Norval,

Thanks for the reply.
I understand that lowering the strut rod bracket holes makes the strut rod parallel with the drive shaft. What I don't understand is why this needs to be done with a 6 link setup. With the stock setupIs it just to minimize yoke travel in the diff? Since you can remove the half shaft and not effect the suspension movement, it is just "along for the ride". I've started using the stock strut location to make the design easier for someone to copy after I am done. If necessary I will make or modify a strut rod bracket with lower ears.

As far a ride height. I was looking at having the outter u joint start 1" lower than the diff u joint. The main reason was for toe change of the wheel. Because the tire is traveling thru an arc with 2" of suspension travel (hard acceleration or cornering) your toe setting will be the same as it was a ride height. I know you have talked about rear end torque steer due to toe change in your car when you pull out to pass a car.

Mark

 

I did nothing to design the 6 link. I just followed the directions on the posts I could find and the magazine articles. Just followed directions and then began my own testing and found the camber curve stayed flat using their setup but the toe was a problem.
I also like the idea that the yokes no long had clips so they could be removed easily for checking for a twisted spline and the 1/2 shafts were no longer part of the suspension.
I have no complaints with following the posted setup.

 

Norval,

I agree with taking the yoke wear out of the equation. That is my bigest reason for doing this. My diff is being rebuilt as we speak and I don't want to ever pay for a complete rebuild again.

On your setup, how much yoke travel to you see?

In my current design I see a .22" of yoke travel in 5" of suspension movement. (2-1/2" plus and 2-1/2" neg of ride height)

Does this sound like too much?

I am starting to think that it does. I also have a design that eliminates yoke travel altogether. This design also keeps the camber change a zero through out the suspension travel. I know you prefer no camber change whitch is a good thing for straight line acceleration. I am trying to compromise and have less camber change than stock but still have some movement for cornering.

Mark

 

ttt

 

I would not do it like that, the stub will move in and out of the case an unnecessary amount, you can greatly reduce it by choosing by positioning it in line w/ the u joints and lower strut pivots, this also allows you to angle the top strut and choose your instantaneous center, the angle of the upper rod will then control the camber curve, the static seting of the camber will slightly move the pivots away from the ideal position but this way the stub movement is minimized.

Here's a pic of where I would place this stuff...

The lower rod is angled straight w. the halfshaft, that way the IC is at it's lowest position and this also brigns down the roll center, too high a roll center in the rear will cause a jacking effect.

The 1/2 shaft determines the position of the IC together with the lower rod, then the upper rod has to be positioned accordingly.

If you follow the revised camber curve of the aftermarket brackets, use those positions and place the upper one accordingly. You can also just draw & calculate it by positioning the 1/2 shaft horizontal and the hub perpendicular to the ground, then move the susp. a certain amount up and angle the hub the amount of degrees you want the camber to gain (so if you want 1/2 a degree gain and you draw a new pos 4" higher you want the hub angled 2 degrees), from that positions you have new locations for the lower strut outer rod (the fork) and then adjusting the inner rod to the correct IC will get you the dimensions you need.

In the pic, the red lines are the intersecting lines for all pivots and the green are supposed to go to IC, this is a rough sketch, bringing the IC closer to the wheel will increase the camber curve, moving it away decreases it.



You may need to tweak the mounts for the upper rod a bit so they don't bind on the halfshaft. I don't have a problem there, I won't have that much suspension travel anyway, it doesn't come real close as the 1/2 shaft won't angle up much before you hit the bump stop but it's still a thing to keep in mind. Pos. the outer mount for the upper rod highermoves it inboard and up so frame clearance is a thing to keep in mind there also.

Parrallel positioned rods will give you NO camber gain, you do NOT want that at all, the rest is done to keep that sub as stationary as possible.

 

No I have about 1/4 inch of travel in the yokes. I ground the end of the yokes right back past the groove and radiused the end. It is suprising how much the yokes move in and out to maintain the zero camber change.

 

Twin Turbo - Beautiful illustration!
How does the design change with a VB Smart Strut bracket that lowers the inboard connection point for the lower strut rod?

 

That's what i'm trying to bring across, the VB&P bracket lowers the inner pivot, this results in a less aggressive camber curve, suited for stiffer springs & shocks and a roll bar. Do you have that bracket? If so, could you measure the difference between the VB&P bracket and the stocker? That way us cheap guys won't have to do all the math and can just copy it and then determine the upper mount easily. It would also enable some of us to do some calculating on it to see if that bracket is really what we want, I'm working on it, i want my roll center lower (not a problem w/ lateral weight transfer, running real wide tires, lowered some stuff & gas tank to lower cg, will not have a lot of susp. travel so slip angle reduction is not a problem)

 

Looks good guys.

Would it be possible to have an adjustable upper bracket ( the one attached to the Diff ) so it is possible to change the camber curve?
Or would both the upper and lower's need to be adjustable?

That way we can all get what we want...

 

Yes, you could use a slot in the bracket and have offset keys to allow you to tinker with the position, I have mentioned this before a couple of times also, the trick is to have the slot drilled inline with the red lines I drew, that way the hole in the key is ALWAYS inline with the u joint and lower pivot, otherwise changine the key also moves the pivot off from ideal. The lower one would then also have to be adjustable and you'd have to have keys that are in pairs, so an upper one and a lower one positioned such that the IC they give is still inline with the halfshaft, otherwise stub movement will be increased again.

 

The only way to determine ride height (or check the 7.9 dimension) from the dimensions you have provided is to measure the centerline of the axle yoke to the top of the fender opening. This dimension is 15.10 on my car. I have solid body mounts so mine is probably a little lower on the frame than later years.

So if you assume you are using a 27 inch tire your ride height at the lip of the fender opening would be:

(27/2)+1.07+15.10=29.67

This dimension would be even higher with a rubber body mount car. This seems a little high to me. A ride height of 27.5 is called out in many assembly manuals.

Note: There are many people on this forum who have access to CAD programs that could help you determine dimensions. If I were looking for geometry information from forum members, it might be nice to supply them with your DXF (at least) information. Or supply a lot more dimensions. As an example, if I "scale" your drawing, it looks like the centerline of your wheel is 12.75 from the ground. Are you using 25.50 in tires? If so, most tires for C3's are 27in. and this will affect the 7.9 dimension.

 

Ok guys, here it is. I just spent 4 hrs in the cad software and this is what I have come up with. All models start with .5 deg camber at ride height and are shown travelling thru a total of 4" of syspension travel (plus 2 and neg 2 from ride height)

Twin Turbo. Here is your model. I completed This model first and came up with .9 deg of camber at 2" of suspension travel. With this design you have yoke travel of .40-.32 of .08" (2mm) with the suspension traveling 2" in each direction of ride height.







Norval. If I understand correctly, this is the system you are decribing. Set up for the same amount of camber gain the total yoke travel is .09"







I have had to split this over more that one post because of the number of pictures. Please continue with the next post.

 

This is a system using the origional strut rod bracket for the lower link. I has been set up the same .9 deg camber angle. No I see that I have a lot of yoke travel, .31"







The reason I was not concerened with the amount of yoke travel is that I had my system configured with a greater camber curve. This is what happens to the system if you drop the inside top link position 7/8". The camber at 2" is now 1.7deg and the total yoke travel is .13" One interesting thing about this setup is that at neg 2" you get negative camber like the stock setup does.








I am still having trouble trying to decide what the amount of camber gain should be over 2 in of suspension travel. For reference here is a stock corvette



And a Smart strut setup. I have droped the strut mount 1-1/2" down.



One of the reasons I was trying to stay with the origional strut rod bracket was for exhaust clearance. In the first few pictures I have a blue circle which is my exhaust.

It now 1:00 o'clock in the morning, and I don't know what to think of all this. Better sleep on it.

Mark

 

Nice models but the top one is not exaclty as I described it, the lower rod should make more of an angle, no way all 3 lines are pointing to the same IC and even if they do, it's almost at infinite. So a combo of the one you drew 1st (with the u joint and 2 rod pivots inline) and pic plus2mark2.jpg would be what I would do, the lower rod has an angle, the upper one also, all meet in IC and movign IC in/out will alter your camber curve, no need for initial camber at ride height, you can adjust the curve to suit yoiur body roll by moving the inner pivots.

 

Twin Turbo,

Ok here is a new design that works as you said it would. The yoke travel is almost zero. I just modified my other design, so this one used the stock strut rod bracket. The camber curve for this design is the same as stock. Stock strut rod bracket and no travel at the yoke. It only makes sense that the camber curve would be the same as stock.







TT, what sort of curve should I be looking to get? Can you give me a value that you would like to see at 2" of travel and what you would like to start with at ride height.

One other thing I am also looking at with these 6 link systems is the amount of toe change. I know TT is not concerened with that because he is not using a single bolt conection for the front of the trailing arm.

Mark.

 

Take a look at John Giovani's 6 link. It may help with the geometery.

http://www.corvettefaq.com/c3/6link/index.html

 

flexusmark, have you given up on the 5 bar design?

 

Mark, yes in your last pics the curve is similar to stock, I didn't say it'd have to be this way, you can reposition the lower pivot a bit lower but then you'll have to move the upper one a bit upwards to keep both pointing at the same IC to minimize stub travel. This will bring the IC more to the left and this will reduce the camber curve. In the above you're gaining just a tad over a degree per inch of travel, with little roll (stiff springs, sway bar, stiffer shocks) you could maybe get away with 1/2 a degree but it really all depends on how much body roll your car has.