6 Link Rear Suspension

[kiwi vet]

Hey All

Just wondering if anyone has any info on 6 Link Rear Suspension article for 80 - 82 Vettes. There is/was a link on www.corvette.faq but it is not working.

I can download the standard one but not the 80 - 82 specific one, as they mention that there are alterations required for these later C3's.

Any assistance appreciated. ;worship

Grant

 

[Twin_Turbo]

There's no 80-82 6 link. LAtely dragvette has released their 6 link but it's for the pre 80 cars, this is all because of the aluminium batwing/lid. You have to do some serious mods for the 6 link to work on the later diff setup. Are you sure you want to go through all that when in reality the biggest problem is the toe control and you have to do away with the trailing arms to cure that , effectively build or install a 5 bar suspension. I haave built a 5 bar setup but am not using it, I'm now building a double a arm rear suspension. If you want to know about the 6 link and 5 bar...just let me know.

Here's the 5 bar I built:

and this is the new double a arm susp

I have pics of the actual thing...but the cad drawings are clearer. (This is a true to scale design of my chassis, it actually looks like that)
(

 

[kiwi vet]

There's no 80-82 6 link. LAtely dragvette has released their 6 link but it's for the pre 80 cars, this is all because of the aluminium batwing/lid. You have to do some serious mods for the 6 link to work on the later diff setup. Are you sure you want to go through all that when in reality the biggest problem is the toe control and you have to do away with the trailing arms to cure that , effectively build or install a 5 bar suspension. I haave built a 5 bar setup but am not using it, I'm now building a double a arm rear suspension. If you want to know about the 6 link and 5 bar...just let me know.

Here's the 5 bar I built:

and this is the new double a arm susp

I have pics of the actual thing...but the cad drawings are clearer. (This is a true to scale design of my chassis, it actually looks like that)
(

Hey TT

Thanks for the reply, that would make sense.
I wonder why they still have the link on www.corvette.faq.com
Initially I thought they would have moved it forward or rearward to clear, but I know you know your stuff, so will move on.

Basically, Im just trying to make this thing handle on our roads, its just so inconsistant in a corner when on the edge, and dont try to change directions quickly it just doesnt want to know, sledging, to oversteering, bouncing etc. You need a boatmasters sailing licence to drive the thing.

Ive been through all the obvious things, shocks, springs etc and tested out of the car, and they all meet or exceed specification.
Is there a standard fix for the C2/C3 chassis, without going to the extent that you are working with to make these things handle like sports cars?.

(Very inpressed by the way, looks like the stuff you see on professional race teams, can wait for your car to be completed).

Cheers Grant

 

[Peer81]

Damn just been typing for a hour or so and do other things, pushed post.. and i wasn't logged in anymore, bye bye post.. So here it goes again... short version.)

I'm also looking into some changes of the c3 rear suspension as you are Grant.

I'm very curious what the 80-82 6 link would have looked like, but i'm afraid they connected the upper arms to the diff which i don't like. The bolts that press the badwing to the diff are not calculated for big (change in) forces and putting forces in a 90 degree angle to the alu diff also isn't a good idea.

For the problems of the c3 rear suspension I'm going through old threats but i can't find a clear analyses of the suspension and what is wrong with it. But looking at TT's and Norval's topics i think you can subdivide the problems into different parts.

- trailingarm. Because the trailingarm is a one point connection the "hub" and spindle assembly will make an arch around this point changing caster if I'm correct?.. This could be "corrected" with a dubble wish bone ala c4.
- To much change in camber during suspension travel.
With the 5 and 6 link packages you see that the strutrod is positioned more equal to the half shaft. So if there are brackets on the market to lower the strutrod at the diff you would get a smoother camber change. But i don't know what the effects will be for the other suspension characteristics. Also viewed from the top down you see the strutrod "crossing" the half shaft. Would it be better to correct its position and move it more to the front of the diff, so it also would become more equal to the half shaft?
- To little toe control.
Maybe this could be corrected putting a c4 toe assembly on your diff (modify it here and there). But i think the tie rods on the assembly still leave some room for toe change. When you want to have a almost zero toe change (i read in a older topic TT wanted to do this) you will need something else.
I know TT started with a c4 assembly but later on changed it to his own toe assembly but i don't know why. Maybe he could shed some light on this?
I also don't know if you need the dubble wish bone structure to correct the toe problem or if this will also work with the normal trailingarm?
-half shafts. Last one are the half shafts. Now they are a part of the active suspension. But the 6 link takes it out of the active part and makes it only for propolsion. Disadvantage is that you don't have a good point to locate the upper rods. And with the upper rods in place the half shafts well move more in and out your diff. Your c clips don't allow this, so you'll need to remove the c clips. Also i'm still afraid the yokes will bend a little because of the forces on it, but i could be wrong!

I'm still looking around but i'm not planning on cutting up my rear suspension for a 5 link. If the biggest problems could be solved with changing the strutrods and putting on a toe assembly i would be more then happy

I hope somebody could correct my reply because my suspension knowledge is still way below sealevel.

Groeten Peter.

 

[Twin_Turbo]

The 6 link mentioned on CORVETTEFAQ wasn't a 6 link, it was a toe control setup. It was a bracket bolted to the back of an aluminium diff to supply a mounting platform for a toe control setup like the C4. However, the car still used trailing arms so something is a miss there, you can't use toe control rods with the stock shimmed trailing arms, the only way would be to just use the trailing arm bolts as locator pins and allow the assembly to slide (not using shims) but I'm not sure if they did it like that. It would be the easiest way to get rid of the toe control problem.

The toe control problem is the major C3 IRS problem. Like you said, the susp. scribes an arch and the trailing arm pivots at a fixed point, this changes to over the entire suspension travel. A bad thing! That was fixed w/ the C4, they have the dog bones, a set of sectioned trailing rods. There are 2 to control hub stability (rotation resistance) and because they are sectioned they allow free movement, a set of rear toe control rods controls toe obviously.

I used to have a mockup Dana 36 IRS from a late C4 (it had integrated parking brakes in the calipers, the earlier ones have drum praking brakes) The later models have a bette roll center than the early C4s which suffer from a jcking effect due to a high roll center (during cornering the outboard wheel jacks up the diff like a pole vaulter giving a severely reduced contact patch and a sudden loss of grip/reduced slip angle)

However I didn't use it, first it was a mockup ..the 36 is a weak unit, secondly the toe control is not 100% accurate and third the trackwidth is much wider and with my wheels that would mean even larger flares...too large. It uses a centrally located inner mount and long rods to give control that mimics the susp. travel but not perfectly. The longer rods give less angular effect and the toe control is off the more you get away from the neutral (straight halfshaft) pos. A better approach is building it w/ a toe control rod that hinges parallel and in line w/ the halfshaft and it's 2 u joitns. Then it will always be dead on eprfect (and that's what I built for my 5 link...the project that I dropped although finished...stepping up to double a arms)

The camber control is good on a stock C3, if the stub axles are tight and the clutch pack too..giving a slop free stub axle. This because the halfshaft is the upper control member (this is also true for the C4 susp). A 6 link adds 2 upper bars to allow you to remove the halfshaft as a geometric control member. Dragvette recently released a kit. They have no clear recommendation on what to do w/ the stub axle clip. However, for a true independence it's best removed and the bars so adjsuted that the stub is pulled a tiny amount out off the diff. However, there's a trucky part here. The rods must be placed absolutely eprfect for the pivots to be in line w/ each other and the u jonts and the 2 rods and the halfshaft have to point to the same instantaneous center. I'm certain they have that figured out properly but small tolerances will affect things, that's why I believe the clip is best removed. I think Norval was one of the 1st to install a 6 link. However these kits are for older differentials and can't be mounted on the later ones. I welded a subframe on my chassis for that, but decided the subframe would be perfectly suited for an upper control arm , the geometry is the same for 6 links and for double a arms, the arms just incorproate toe control and wheel axis location so another plane (birdseye view)

The only need for reduced camber gain is NOT because it always makes the car handle better, it may not. It has to do w/ lowering, the roll center , the center of gravity and most important body roll. Body roll is the result of lateral weight shift during conering (centrigugal force), so it's the weight shift that induces the roll...not the roll that induces thbe weight shift. The rolling is the suspension absorbing some of the weight shift. I have reduced body roll by lowering the CG, the roll center in the rear is raised, as is the front (the front being particularly poor, you can use some additional camber gain there, a longer uppre ball joint will help) and I have siff springs and roll bars. I have 400rera and 450 front springs, however they are all moutned on the spindle - rear- and on the control arm near the ball joint - front- so that the spring rate is much closer to the wheel rate (stock it's a nutcracker principle, the spring receives a higher load because the wheel is on the handle side of the nutcracker and the cross shaft is the hinge). This means I will have significantly less body roll. This gives 2 other problems, the load on the tires is severely increased, that's why I'm going to be running very wide tires front and back and with the stiff suspension the load put into the frame is increased also. No use in having a stiff suspension mounted on a weak frame, you won't be able to dial in or use the suspension if the frame is like a soft noodle, the frame will "soften" the susopension characterstics but in an unpredictable way. That's why I have all the frame mods.

There's a reason behind all the mods I've done, the coil overs, the dyno tuned and valved shocks (custom valved and dyno tested for resutls at varios shock oil temps) and so on.

Equal struts in a 6 link give NO camber change, something you don't want unless you're a drag racer strictly.

Stock trailing arm suspension

my 5 bar:

The forward mount

The toe control was not installed there yet. This is how I was going to do the toe control, never finished because of double a arms. However I do have all the design drawings for the toe control plate (and the toe control mounts on the hubcarriers were in place)

See those 4 allen bolts? Those 4 round bosses are cast into all the batwings, they are PERFECT for drilling and tapping (M12 allen heads), they are not in the same plane but nothing a simple set of spacers can't fix (on the top bosses) or an angled plate. This allows easy mounting of a toe control plate:

Here's how it is done ...this is the pic that was called 6 link!

A c4 toe control setup on a 80-82 diff by doing exactly what I did above, drilling and tapping those 4 studs. This car still uses the trialing arms, apparent by the coil overs (they are mounted on a bracket made of U channel welded to a trailing arm, these mods have all been done by acp in germany..that's how they mount it) so they must have removed the trailing arm shims, othrewide it'll bind. If they did, rpetty neat...and a cheap way to get rid of the toe control problem, cheaper and easier than building a complete C4 type suspension. However, since the shocks (coil overs) are mounted on the trailing arm this stresses them outboard (since the shocks are angled) that means that the trialing arm isn't free to move, the toe control rods have both the toe control force on them and part of the load that pushes the arm outside (since the coil overs mount front of the halfshaft)...for a proper free movement and recued load on the rod it'd be best to locate the shocks as close to the bearing carrier as possible.

Another thing is, it uses the central C4 mount, kind of a shame..it'd have been pretty east to build a bracket w/ 2 5/8th holes for 5/8 bolts and rod ends directly insight of the inner u joint..then toe control would be perfect.

This is my Toe control plate design (abandoned it, have a rough mockup..wanted to have it water jet cut..no use now)

Here's some shots of my mods:

Part of the rear lower arm mount, repositioned for a new wheel center (moved wheel axis backwards so it's centered in the L88 flares, most cars you see w/ those flares look like the wheels are too far forward, this because of the design of the flares...I think it's ugly so why not move the wheel back, the diff is also placed slightly further back) The rod end is for marking where the forward mount has to be on the pinion crossmember (although the threaded rod is not adjusted proeprly in the pic, it has to be parallel w/ the beams above the diff)

C4 Dana 44 & differnetial oil cooler pump / custom pinion mount (C4 uses a c beam...no room for that)

My chassis:

Here's my double a arm susp. design (I have already started building this)

same w/ cantilever shock setup and a billet aluminium lower arm (gotta figure out how much $$$ to have that milled)

Almost finished the uprights:

 

[kiwi vet]

Hey TT

Firstly let me say, Im very very impressed with your designs - WOW! and the CAD drawings to boot, very clever and methodical, a great combination! What software are you using?

I supposed you have a vested interest in this level of specific design and engineering, as with that powerhouse motor you've got planned, and the projected resultant speeds and forces that will be created, its more a case of self preservation - right!

In my case I do not believe I need this level of sofistication, neither the car nor the driver will ever be in at this level of performance on the street.

Actually, on second thought, maybe it should read "the driver will never be at this level of performance!!!"

Anyway, moving on, I am interested in your design for the toe control plate idea. If I understand this theory (reality) correctly, you are trying to bring the rotational axis of the arms in alignment with the half shaft rotational axis, that makes sense and allows control of the camber changes through the total movement of the hub, maintaining a more controlled vertical position through out the suspension range of travel. Is that correct? I dont quite get how this affects toe, as to me its more camber control, unless what your saying that with camber fluctuations of the existing system cause toe variables as well.

At the shim end, a spherical bearing (rod end) would be suitable to deal with the rotational movements of the trailing arm satifactorily to stop binding issues, however how would you locate/secure this bearing to stop movement along the location pin, without restricting its freedom. Failure to locate this surely would result in the leading location point of the trailing arm to move accross the car up to 30 - 40mm back and forth, creating massive and inconsistant changes in the toe as a result. Your thoughts?

Assuming the above can be solved, and Im sure there is an answer (shorten trailing arm, spherical bearing and custom bracket?), we are then left with the spring and shock.

Firstly (and I know Im going to regret this! :L)
What is wrong with an upgraded fibreglass spring - for a road car?

Is it possible to complete the toe bracket/rod system as per your design and trailing arm treatment as above (somehow) while retaining the leaf spring? I also understand I will have to lower the lower arm pivot points to also align with the half shaft axis which I believe can be achieved through packing the strut rod carrier bracket down. Thus resulting in everything parallel at rest (half shafts, lower arms and upper arms - yes?)

As I said, my goal is to get the vette just to drive like a normal sports car (rather than the ship variety), for the type of roads here (read bumpy and winding) rather than create a track car. Also cost is an issue.

I await yours and any other comments with anticipation. ;worship

Grant

 

[Twin_Turbo]

Hey TT

Firstly let me say, Im very very impressed with your designs - WOW! and the CAD drawings to boot, very clever and methodical, a great combination! What software are you using?

SolidWorks 2006

I supposed you have a vested interest in this level of specific design and engineering, as with that powerhouse motor you've got planned, and the projected resultant speeds and forces that will be created, its more a case of self preservation - right!

No, just gettiong the best handling possible, attacking the obvious flaws in the stock design. All is concentrated on fixing the toe problem in the rear, customizing camber for the body roll characteristics and fixing bump steer in the front and switching to end take off front steer because it has benefits over rear steer (has to do w/ bushing deflection and steering input...if you want to know..just say so)

In my case I do not believe I need this level of sofistication, neither the car nor the driver will ever be in at this level of performance on the street.

Actually, on second thought, maybe it should read "the driver will never be at this level of performance!!!"

Well, attacking the toe steer problem will make the car much easier to predict when it comes to rear stability

Anyway, moving on, I am interested in your design for the toe control plate idea. If I understand this theory (reality) correctly, you are trying to bring the rotational axis of the arms in alignment with the half shaft rotational axis, that makes sense and allows control of the camber changes through the total movement of the hub, maintaining a more controlled vertical position through out the suspension range of travel. Is that correct? I dont quite get how this affects toe, as to me its more camber control, unless what your saying that with camber fluctuations of the existing system cause toe variables as well.

It's not the rotational axis (seen from the side) that's the problem, that only gives a changing wheel axis center vs. the wheel well. The toe control problem is the problem where the trailing arm is fixed in position on the front and when the suspension moves the halfshaft and strut rod's horizontal resultant component changes (with the halfshaft horizontal the full length = the horizontal component, in any other position the angular effect effectively shrotens the horizontal resultant, in effect the wheel moves in and outboard seen from the back)
This means that as the suspension swings it makes an arch (seen from the back) and this means the attitude of the trailing arm changes, it's angle towards to front mounts. THIS is the toe setting and provides stability at speed. When the toe changes during suspension movement you are inviting a big problem, especially during cornering where one wheel bumps and the other rebounds, if the toe changes you can get a sudden toe steering problem making the rear wiggly, hard to control and even scary unstable, easy to spin out.
It's all about TOE, not camber! Camber has to be taylored to the vehicle's roll characteristics (dependant on roll center, Cg height, rpings, shocks and sway bars) Static (or initial) camber can be set, the curve (gain and/or loss through movement) is designed into the inner pivot point of the strut rod, it's a geometric resultant of the virutal swing arm (arm from hub to instantaneous center)

At the shim end, a spherical bearing (rod end) would be suitable to deal with the rotational movements of the trailing arm satifactorily to stop binding issues, however how would you locate/secure this bearing to stop movement along the location pin, without restricting its freedom. Failure to locate this surely would result in the leading location point of the trailing arm to move accross the car up to 30 - 40mm back and forth, creating massive and inconsistant changes in the toe as a result. Your thoughts?

A rod end is ALWAYS a good idea. Because of the toe problem the bushing does not only rotate but also it distorts. This is the reason why I think a poly bushing there is a bad idea. Poly is much stiffer and thus puts more load into the through bolt. A spherical bushing is a good idea but metal on metal is not great for a cruiser and the spherical ends wear (however you can seal them off w/ boots and load up the boots w/ grease and get a much longer life out of them), there is a different solution though. A Johnny bushing is a combo of a spherical bearing and a bushing, best solution IMO.

With the germans using toe control rods at the back the front mount HAS to be a floating moutn, otherwise the arch movement will want to move the back of the arm in and out, with the rods that can't happen so if you use those rods to set the toe the front has to be floating. This will work but I'd be worried about the through bolt wearing out and snapping and the frame pocket isn't very large so you may be limited in the toe setting and suspension movement before the arm hits the pocket sides. That's why the C4 type sectioned trailing rods is the best way to do it, you have positive locating of both sides (frame and hub) and independant toe control

Assuming the above can be solved, and Im sure there is an answer (shorten trailing arm, spherical bearing and custom bracket?), we are then left with the spring and shock.

I think you are talking about the wrong thing, please read the entire thing again. The arm (in the german method) is only allowed to slide freely over the front bushing, the arm is still positioned in the frame by the through bolt.

Springs and shocks don't influence this, although the coil overs in the german pic do load up the trailing arm forward of the hub and this increases the toe control load

Firstly (and I know Im going to regret this! :L)
What is wrong with an upgraded fibreglass spring - for a road car?

Buggy springs...on a sports car...! LOL Well, there's a big drawback w/ these springs, apart from weight (can be "cured" w/ a composite spring)..it's transverse harmonics. All springs carry harmonics and the problem is, these springs carry harmonics from left to right and vice versa. I assume you know how simple harmonics and wave theory works w/ longitudinal and transversal waves, wave lengths, knots, amplitude..yadda...yadda... Then you probably know that 1 fixed point is not very effective at stopping waves passing through, many frequencies in a certain length spring will have the right frequency to have a knot located at the mounting point, which makes for unobstructed wave travel. The C3 uses that..a single mount. Later cars and aftermarket stuff use dual mounts to improve this. Further, a transverse leaf acts as a leaf and as a sort of sway abr because of this influence from left to right. It takes away from true independence and spring rates affect roll stability not only because of the spring rate but also because of it acting as sort of a sway bar. This is crudely put but it does illustrate why a leaf is not ideal (however in suspension systems everything is a compromise...)

Is it possible to complete the toe bracket/rod system as per your design and trailing arm treatment as above (somehow) while retaining the leaf spring? I also understand I will have to lower the lower arm pivot points to also align with the half shaft axis which I believe can be achieved through packing the strut rod carrier bracket down. Thus resulting in everything parallel at rest (half shafts, lower arms and upper arms - yes?)

Sure you can keep the leaf spring, no problem. With the end bolts being that long and the bushing/ppedestal mount there's luittle effect on toe control from the spring. Why do you want to move the lower strut to be parallel w/ the halfshaft? You will get NO camber change that way, just static...and that's it. I would not tinker with that unless you have a profound idea of the roll characteristcs and suspension design. If you change the angles and pivots you change the virtual swing arm, the instantaneous center and the roll center!! Parallel is NOT good (no virtual swing arm , instantaneous center at infinite)

As I said, my goal is to get the vette just to drive like a normal sports car (rather than the ship variety), for the type of roads here (read bumpy and
winding) rather than create a track car. Also cost is an issue.

That's why you don't want the components parallel. I assume you don't want a harsh ride? If so, concentrate on softer springs, quality shocks, no sway bar in the back and possibly fixing the toe control problem.

I await yours and any other comments with anticipation. ;worship

Ok

Grant

 

[kiwi vet]

Got it???????????????

Thanks TT

I got it now (I think?) Well at least on the same page! .

I also have downloaded and read through the Greenwood VIP (vette improvement program) for IRS Vettes on corvette.faq. Which has also highlighted the toe out result of suspension movement, as you have mentioned.

"Why do you want to move the lower strut to be parallel w/ the halfshaft? You will get NO camber change that way, just static...and that's it"

I had read somewhere that lowering the attachment point of the strut arms lowered the camber change and the squat under acceleration. Also the 6 link photo in the download for pre 80 C3's shows the links basically parrallel.

Greenwood's advice (as above) goes further to specifcally set the half shaft inner universal centre 1/2" higher than the outer universal centre (assumes you've levelled the chassis first) then adjustment with diff height and lowering of strut bracket 1/2" to reduce camber change, lower ride height and restore CG, so I had half of the info right, just enough to be dangerous! .

I might try the Greenwood recomendations as an interim measure, and see how it goes, as it seems sound advice and I'm also suffering from Dollerous Minimus at present, so its a relatively cheap exercise to explore. And honestly, almost anything would be better than what Im starting with.

I would be interested in your comments on Greenwood's recomendations in modern times if you wouldnt mind, as I dont know how old this info is, http://www.corvettefaq.com/c3/vip.pdf

Again thanks for your indepth help (and patience) with this subject to date.

Cheers Grant

 

[Peer81]

I think, I understand it now.
So basically the upgrade from the c3 one trailingarm to the 2 dog bone's on the c4 is the better control of caster? (the angle the wheelhub is making) because the bushings are mounted vertically and not horizontally. But through the dog bones you now have two connections between the wheelhub and the "chassis" . So when the half shaft is moved by body roll it makes an arch. With the trailingarm this is a problem because it only has one connection that can move (or forced to move) this is most of the times a "toe out" as a result. With the dog bones you still have the same connections but now you have two. The first one is still forced to follow the angle of the half shaft, but the second connection is making a counter angle because the toe shafts are keeping the hub generally in the same toe "area". I think this would be correct?

So to make a toe improvement on a c3, you will need a second rod to fix the hub for horizontal movement and you will need a second connection (section) in the trailingarm to counteract the angle the trailingarm is forced to make.
Hemi joints are not a good idea on a normal streetcar (for the dog bones) so you have to get normal rubber bushings. The tolerance in the bushings is enough to correct the toe problem so getting poly bushings would be a bad idea..?
So the conclusion would be the easiest thing to do is make a five link with normal rubber bushings.


I come to this conclusion because I think the bushings in the c4 dog bone's are there to make vertical movement possible and not horizontal. So the horizontal is just the "flex" of the bushing... Just an thought.

Groeten Peter.

 

[Twin_Turbo]

I think, I understand it now.
So basically the upgrade from the c3 one trailingarm to the 2 dog bone's on the c4 is the better control of caster? (the angle the wheelhub is making) because the bushings are mounted vertically and not horizontally.

No, TOE. Caster is of no interest on the rear suspension, caster is the offset of the steering axis (kingpin inclination) with the wheel centerline, just like the casters on a shopping trolley..they trail behind the steering axis, this gives stability. The 2 dogbones allow the suspension to move up and down without the forward mount setting the toe and changing it. It has nothing to do with how the bushings are located, and the dogbones have them mounted in the same way as the forward stock trailing arm mount.

Look at the CAD drawing of the stock trailing arm suspension. You see the 2 green trailing arms, their angle to the front is also the angle of the wheel hub, the TOE angle. This angle is set by the hub position, how far it's outboard or inboard and the front trailig arm mount (grey frame pocket in drawing). The front mount is what you shim to set static toe @ ride height. Now imagine the suspension moving. As the suspension moves away from the pos. where the halfshaft is parallel the wheekl moves inboard both in bump and rebound. @ horizontal halfshaft pos the wheel is outboard the furthest. This means that you are constantly chaging toe and if you set toe @ horiz. halfshaft or close to it, any position elsewhere in the suspension travel changes the toe to OUT! That's just about as bad as you could possibly get it. If you would set enough initial toe to largely eliminate the worst toe out situation at the suspension extreme that your car sees 9depends on spring and shocks, stiffer obviously gives less overall travel) then it would give too much toe in at horizontal and the tires will wear out quickly. This is why stiff springs and shocks help, it's a patch..they allow much less suspension travel masking the toe control issues.

But through the dog bones you now have two connections between the wheelhub and the "chassis" . So when the half shaft is moved by body roll it makes an arch. With the trailingarm this is a problem because it only has one connection that can move (or forced to move) this is most of the times a "toe out" as a result. With the dog bones you still have the same connections but now you have two. The first one is still forced to follow the angle of the half shaft, but the second connection is making a counter angle because the toe shafts are keeping the hub generally in the same toe "area". I think this would be correct?

The 2 dog bones indeed have 2 connections and they have a mutual virtual swing arm 9they make up the arm w/ their angle and extended instantaneous center) The dog bones can hionge at 2 points, at the frame and at the hub. This means the hub is NOT rigidly attached to the forward arm like stock. This means that the dog bones offer NO toe control or toe influence. It has nothing to do with hub rotation, that's a factor of the virtual swing arm, the 2 dog bone angles and attachment on the frame and hub. With the rods parallel the hub does nto rotate but then you have an infinite swing arm resulting in anti squat loss. I have no idea what you are talking about, it just doesn't make sense.

So to make a toe improvement on a c3, you will need a second rod to fix the hub for horizontal movement and you will need a second connection (section) in the trailingarm to counteract the angle the trailingarm is forced to make.
Hemi joints are not a good idea on a normal streetcar (for the dog bones) so you have to get normal rubber bushings. The tolerance in the bushings is enough to correct the toe problem so getting poly bushings would be a bad idea..?
So the conclusion would be the easiest thing to do is make a five link with normal rubber bushings.

Toe control improvement is done with toe control rods and ELIMINATING the trailing arm as the toe control member, so this means the trailing arm has to be able to float on the front mount or you have to replace it w/ a sectioned arm. The dog dones are 2 sectioned arms in pair because they allow a virtual swing arm and huib control (otherwise there is no hub yaw stability because there is no ridig upper arm to control it, that's why you need 2 of those forward rods/dogbones)
HEIM joints are not a problem, you can get seals for them and lube them up (the ones w/ a zerk are not recommended) the only drawback apart from frequenter replacement is harshness as it's basically metal on metal. You could use dog bones like the C4 and use rubber bushings. Again poly is a bad idea there because there's both sideway deflection and rotation, poly is pretty stiff. Johnny joints would be an option also.

I come to this conclusion because I think the bushings in the c4 dog bone's are there to make vertical movement possible and not horizontal. So the horizontal is just the "flex" of the bushing... Just an thought.

The C4 uses bushings because bushings are dirt cheap, it's always the bean counters at work. The idea behind the 5 bar (not link) is not rigifity of bushings, bushings don't offer control, geometry does.

Simply put, the 2 forward rods/dogbones replace the trailing arm. They are double sectionsed. This so they offer no rigid hub mount and therefore no toe control/influence. There's 2 of them to control huib jaw (otherwise when the wheel turns the hub will rotate and move forward and backward), the 2 together give a virtual swing arm with a (dynamic) instantaneous center. The length of these affects angular effect, the angle between the 2 rods and the mounting points determine the virutal swing arm. This arm influences the anti squat characteristics of the IRS.
For the rest the 5 bar is the same as the C3 setup, camber control is still done w/ a lower camber rod and the 1/2 shaft, exactly the same (and cheap... beancounters yet again). Toe is controlled w/ the toe control rod, where toe is controlled in the C2/3 w/ the trailing arm's forwart attitude (shimmed frame pocket position inboard/outboard)

I would suggest you guys read up on suspension design and dynamics, this stuff isn't just something to go and modify without a thorough understanding of how to actually do it and what affect your change has. Changing one thing changes many others because different elements share geometry control and therefore will influence more than what you are initially aiming at. For instance, the virtual swing arm affects anti squat but also the hub yaw. Hub yaw, if kept to a minimum is not a problem with bushed camber rods. It is even less of a problem with rod ends. However it should be kept to a minimum as it does affect the camber curve and if you have a cable operated parking brake it can affect that also.

Groeten Peter.

 

[yellow77]

Well, TT, after reading all your inputs, I am scared to drive my C3. The steeroids system uses spherical bearings at inner and outer tie rod ends which are not greasable, and I have poly bushings at the front of the trailing arms.
Also, with the ride height set with almost an inch and a half between the tire and the rear wheel arch, even with no shims on the inboard side of the bushing I have 1/32" toe OUT!.

I dont think the frame is damaged, under compression the toe will move towards 0, if not toe in (slight that it might be).

I have a question regarding the TOE situation, have you seen cars with this TOE arrangement at the rear?, also as you can imagine, the car is unstable at speed especially in long sweeping curves.

Cheers

Richard

 

[Twin_Turbo]

Well, TT, after reading all your inputs, I am scared to drive my C3. The steeroids system uses spherical bearings at inner and outer tie rod ends which are not greasable, and I have poly bushings at the front of the trailing arms.
Also, with the ride height set with almost an inch and a half between the tire and the rear wheel arch, even with no shims on the inboard side of the bushing I have 1/32" toe OUT!.

I dont think the frame is damaged, under compression the toe will move towards 0, if not toe in (slight that it might be).

Can't you get it to 0 toe at least?? Something must be out of whack, have you checked your stub axles and camber rods?

I have a question regarding the TOE situation, have you seen cars with this TOE arrangement at the rear?, also as you can imagine, the car is unstable at speed especially in long sweeping curves.

Cheers

Richard

? What do you mean, cars with a similar suspension..i.e. with a trailing arm suspension? Not like the corvette, a lot of cars use a semi trailing arm suspension. As far as I know, only the c2 & C3 corvette have the suspension like this. that doesn't mean that the semi trailing arm is better, it's not really... there is only 1 suspension that is much better than all others, the double a arm (wishbone) suspension, that's why the C5 and c6s have that in the rear and also why I'm going to build that. A properly setup 5 bar will come very close though (especially with the toe control system set up properly....not like the C4)

 

[Twin_Turbo]

I have the a arm setup almost finished, made some slight changes here and there but this is it (I ditched the cantilever setup..way too much work):

 

[Peer81]

Very sharp looking!
Are you still hoping to get this on the street without any big problems by the apk (periodic vehicle inspection)?

Groeten Peter.

 

[kiwi vet]

Looking Good

Well TT

I cant wait to see this completed. It will be a weapon for sure!!!

Grant

 

[Twin_Turbo]

Very sharp looking!
Are you still hoping to get this on the street without any big problems by the apk (periodic vehicle inspection)?

Groeten Peter.

Sure, you can install steeroids and van steel/jim meyers coil overs (with tubular arms) or a vette brakes transverse leaf and make it through the periodic testing so this too will work. They won't know if it's original or not. They won't think I designed and built this myself..how many people do they see on a daily basis with a home built suspension..I figure 0