Hello,

This is my first post to this form, although I have been reading and learning for some time now and I would like to thank everyone for that. I am currently designing a 6 link system for my 78 and thought I would share my progress. I am a mechanical designer with access to a 3D cad system that will allow me to design a complete 6 link system on the computer and deturmine it's performance. At this point I have a working model that I have used to compare a generic 6-link design with the origional corvette design. I have already seen a huge inprovement in camber change as we all know.



For anyone that is interested follow the link below to my web page. There you are able to download a 3D version of my cad model that you will be able to zoom,pan and rotate on your computer. I have also included two drawings that show the difference in camber change between the 6-link and the origional design.


www.flexusautomation.com/corvette.htm

This is just a start to the model. I plan on adding the diferential, cross member, and spring to make it a complete as well as all brackets for the 6-link.

I will update my site as things change as well as post here. Any feedback and coments would be great, and I will be more than willing to share the final design with anyone who is interested.

 

Wow, nice work. Those are some interesting numbers and great models. Did you model it in Solid Works?

Keep in mind that you want some negative camber gain for cornering but you don't want it if you are drag racing and need maximum straight line acceleration.

 

Interesting stuff! It nicely shows the toe change that of course is not desirable.

I'm not sure I agree that camber change is a bad thing. For handling I would think some camber change is good. For drag racing you don't want it, of course.

Looking at your CAD design it doesn't look like it addresses the toe problem?

 

I've been trying to bring that point across for some time, 6 link handles camber and eliminates the 1/2 shaft as a part of the geometry, this means that camber adjustments is easy and the stub is no longer riding the center pin, play on the stubs & c-clip is no longer a problem. However, the trailing arm still hinges at 1 point and w/ the hub arc movement (bump/jounce) it still determines the toe setting and it changes, only way to fix it is to use either a secioned arm (like C4) or a toe control rod on the re and some kind of sliding system at the front (basically turning the front trailing arm mount into a horiz/vertical locator and giving it sideways ability to slide)
This being said, the real advantage of the 6 link is in the stub wear problem, if you have a set of perfect stubs with no play on them only the revised lower bracket will give you the exact same camber curve.

Those cad drawings are awesome, it's for a pre 80 diff setup, can you do the same for the later diff? The only difference is the camber bracket is located further backwards, it won't make any difference for the camber curve and geometry, just has an impact on strut rod design and angles.

I really like the work you did, awesome.

Can you tell me how much you moved the inner mount of the camber strut down (modified bracket)? I have to modify mine and if you have a good number I can just check it and see if it's dead on, might save me a lot of measuring and fooling around w/ inclinometers & strings

 

Awesome work. Nice to see someone with your skills on here. Welcome to the forum.

 

Cool. The toughest part about modeling a real world system is accurately measuring the system to start. (I design in Catia V5.)

-Matt

 

Very nice!

Do you have a file type that I can load up into solid works?

 

"The picture is linked to an EXE file called an E-drawing. The file size is about 2 meg and will open on any computer."

It won't open on this one! I am running the Linux operating system. What does Windows use to open E-drawings?

I can't say that I've ever heard of an "E-drawing" before and find it curious that the extension for these files is ".exe". Very odd, that.

 

Nice Work!!!! Great first post!!! You are the MAN!!

I agree with Twin Turbo's assessment of the IRS geometry. I've been thinking about changing the front trailing arm pivot point to horizontally sliding (no shims) and using dual "camber rods" - essentially modifying the existing camber rod and adding an additional one on each side. They would be in the same plane vertically and connect into the trailing arm level with each other and say 8" apart. Essentially they would move/act together as a lower control arm (in reverse) and eliminate the toe change.
I believe that the rear camber curve needs to remain substantial and that the optimum would be if the negative camber gain would mimic the body roll curve - essentally keeping the rear wheel vertical with the ground through bump-rebound. It would great to see if you could model this and calculate the forces.

The 6 link article in the FQ section is filled with alot of BS regarding toe change, camber change and improvements in C3 handling. I believe the main reason the six link car turned better than the stocker was because they lowered the inside attachment location for the camber rod. By doing so they also lowered the rear roll center, causing the rear tires to take on more of the cornering forces. You'll notice they describe the non-6 link car as pushing and tearing up it's front tires. It would be great to see modeling done with the inside camber rod attachment point lowered by .5 to 1 inches as well. If not - thats cool too. Anyway, welcome to the forum - awesome first post!!!!

 

It's a windows application that lets you view the drawings (zoom/rotate etc). Try to run it from inside a windows emulator.

 

FLEXUSMARK, I sure would like to have an IGES, parasolid or STEP file of that assembly. I can understand that you may not want to distribute these files. I would like to model the front suspension, maybe we could trade models. With front and rear suspension done, it would be easy to do the frame and connect everything together! If interested, please E-mail or PM me

 

Curious what dimensions you are using to locate your pivot points. Any chance you used the dimensions from the Giovanni kit that was available back in the late 80's and early 90's. The dimensions can be found on Giovanni's patent for the system (#5,046,753 dated Sep. 10,1991) by going to the web site for patents and looking it up. I laid the dimensions out in AutoCad some time ago looking at the in and out motion of the side-yolks. In any case, the modeling looks quite nice, good work.

 

WOW!

Nice work. Now hurry up and make the blueprints will ya!!!!

Are you done yet!!

Seriously though there are a lot of people interested in this. For the sake of 3 brackets and two more strut rods you can make a great improvement to these cars. If you can get it to bolt to the existing mounting ponits for the rear sway bar on the trailing arms and the differential mounting point on the cross member it will be even better.

Pete

 

wow, very nice. Any chance you are going to model a 5 link system anytime soon?

 

That's really great! I would be really interested about iges or step files too! Infact we have a plan to model C3 Corvette totally in CAD. I've been speaking about this thing for about a year now, but as this is only a hobby I haven't got much work done yet... Mainly our time has gone to putting up our new site (check my sig). Now it's about the time to start the modelling... I have done some minor modelling, but hopefully I will get to more exciting parts soon... Last winter I modelled rear trailing arm, but it seems that you have a lot other things already modelled!

 

Wow! Very impressive, especially the animations!

I'm running Solid Edge so we are both using the parasolid kernal. Let me know if there is something I could contribute. Looks like you have it handled though.

This should clear up a lot of the suspension discussions here. I'm looking forward to the updates. Again, kudos to you!

 

Wow that is nicely done Welcome to the forum

 

Welcome to the forum!

Looks very nice, but I've got a question

Do you currently have an equal-link-length setup with parallel links? if so, why?

A parallel, equal-length setup is not at all what you want for a vehicle suspension unless you're only going to go straight down the road. It makes the system into a parallelogram linkage, which is great for ride-camber, but it also creates a roll-camber coefficient of 1.0. That is a bad thing. That means that when the car rolls 1 degree, the tire cambers 1 degree, so the tires are always vertical...with respect to the body. So in a turn, you have tires that are cambering out from the turn.

In a typical dual A-arm suspension setup, the upper link is shorter than the lower. This is done specifically for camber gain. With a camber gain of maybe 0.6 instead of 1.0, you get 0.4 degrees less 'bad' camber. If you look specifically at the outside wheel (easier to visualize), as you corner, less roll camber brings that tire closer to vertical. The roll-camber number can be a little confusing at first, since it's relative to the BODY and not the ground. So a roll-camber of 0 would mean that the tire is always vertical (like a solid axle) and a negative roll-camber would mean that the tire would actually roll INTO the corner. Maybe possible geometrically, but impractical for lots of reasons.

Granted, how good or bad the geometry is also depends on the initial starting point, i.e. where in the camber curve the vehicle is normally trimmed.

What I keep wondering is why isn't there anyone just swapping a newer rear suspension into a C3? Pull the rear suspension out of a modern RWD car and graft it in. Maybe like a CTS or something.

 

dave, you are correct, one problem however of the need to gain neg. camber is that you need the upper arm either shorter or at a different angle (inner mount lower / closer to 1/2 shaft) but this also makes that during travel at full bump & jounce the stub is pressed all the way into the diff and at ride height or level suspension it's sticking out, this means that you have to take great care to determine that you have some play left at full bump & jounce, otherwise the 1/2 shaft stub will bottom out in the diff w/ potential disastrous results. It isn't a hard thing to correct for, it just requires careful setting of the upper arm, then the lower arm for the camber setting.

 

Right. The plunge of the splines is certainly an issue. You probably don't want the halfshaft coming out of the differential while you're driving. I think that might be a bad thing. Somewhat less bad would be trying to plunge the halfshaft through the differential.

One relatively simple way around it would be to have a set of halfshafts built up with tri-pots on the inner side instead of trying to plunge the spline. A spline under torque really doesn't like to plunge. I wonder if any of the normal custom driveshaft companies would/could make up a shaft with tri-pots. I would imagine they would. If they make halfshafts, they have to deal with them.