Brutus

This is another version of the 6 point rear end link from Tom's Differentials. Does anyone have any comments on their product at all? http://www.tomsdifferentials.com/cat24.htm
I have my rear yolks out of the diff and they appear to have had the C clip groove and the remaining part of the yolk machined off at some time in the past. I'm in a dilemma right now because replacement yolks are not exactly easy to find over here, however if I went with a 6 point addition to the rear suspension then replacing the yolks would be negated.
I'm running out of options and Summer is disappearing fast.

MikeC

There is a topic in the recent past by Norvalwilhelm. He built his own and he said it wasn't too hard. Fairly cheap too. Just take your time to design it reight before you install it.


[Modified by MikeC, 7:28 PM 1/17/2002]

MikeC

Here's the shortcut http://forums.corvetteforum.com/zerothread?id=202751

gearheadz

I'm getting ready to do my entire rear suspension & have been considering Tom's stuff. I think I'm gonna make my own (like Norval)...$450 for four heim joints, two threaded rods & some brackets is too much dinero.

Mark

Brutus

I don't have a problem making my own either Mark it's just that the finer points of the overall geometry of it's design have me a little lost.
If Norval, Stingy74 or someone else could come up with some more exacting measurements for the rest of us to work with then cobbling all the bits and pieces together would be a much simpler task. How about it please guys? The pics are great and very helpful, but a measurement or two would go along way towards pointing the rest of us in the right direction.
Going this route would certainly negate the hassles I'm having trying to locate new yolks.

DeenHylton

I called Toms Differentials a few days ago and asked about their 6-link set up. You also need to purchase their swing arms for everything to bolt together. They also said that one end of the upper link attachement is slotted(if you look closely at their picture it's the end closest to the center section)...this allows the upper strut to slide back and forth...that's how they get away with getting the suspension in a bind. I'm assuming they must still be using an axle C-clip to maintain wheel alignment??? Deen

norvalwilhelm

I can't see spending $450 for a few struts and brackets. The top link is 13.5 inches center of rod end to center of rod end. The lower inner strut point is dropped about 2 inches from it's present location. If you draw a line through the bottom inner strut hole old of new straight up this goes through the inner upper mount. Someone posted a great article on this and I can send it to anyone who needs it.
Drop the lower strut paralled to the drive shaft or approximately 2 inches
Make a upper strut 13.5 inches with a left and right 5/8 rod end
Mount this upper strut to a stud welded to the crossmember but line up vertially both the upper and lower inner rod ends
Make the upper outer strut rod bracket and weld or bolt the trailing arm. Make it long enough to attach the 13.5 inch strut rod
I used 1 inch hex alumimun 6061T6 and tapped it 5/8 left and right.
The yoke clips can not be used. Toe and camber changes are a breeze.
Good luck
Norval

MikeC

Norval,
Send that article my way, please.

Thanks,

Mike

mvwjd

Norval,
Could you please send that article to me also?
Thanks,
Bill

flynhi

Hi Norval,
Please send the article you mentioned to me at:
will_shepherd@hotmail.com
Thanks very much,
Will

dladd74roadster

Norval implied the key. Here it is explicitly:

The upper link and lower link HAVE to be parallel AND the same length so that during suspension travel the camber doesn't change. And optimally the links will be parallel to the half shaft. But if you want to use the original lower strut rod and it's original location, you would just have to make sure that you mounted the outside upper link lower on the trailing arm creating the all important parallelogram. If you already have the equipment it would be far cheaper to do this yourself just as Norval has done. Although, I hadn't thought of the idea of the bracket bolting between the diff. and the crossmember serving both sides. That seems pretty slick. I don't think that would be too difficult to replicate yourself as well.

dl


[Modified by dladd74roadster, 12:23 PM 1/18/2002]


[Modified by dladd74roadster, 12:24 PM 1/18/2002]

427V8

OK it's time for me to rear my ugly head and disagree....again.

I've been reading suspension design books and think I know something :rolleyes:

IMHO
From what I've read you do not want the upper and lower links parallel nor the same length. I do like the upper link concept ,I just feel it can be improved a LOT with some work :D

Why?
Parallel, equal length links ( If they are also parallel to the ground) set the wheels roll center at infinitiy. So as the car goes over a bump the tire goes straight up and down. ( BTW if the links are not parallel to the ground the wheel will not go straight up and down but rather at an angle to the road :bb )

While that sounds great, the problem comes in during a corner. When the body rolls, the equal length arms cause the a camber GAIN ( more positive camber ) on the outside wheel! This is because the roll of the body causes the upper link to move out of the corner and the lower link to move into the corner.
This is normally fixed by using very stiff springs and Sway bars to limit body roll but then you have the stiff ride problem.

By using unequal length upper and lower links AND making the links not parallel and not parallel with the ground, but rather angle towards eachother at the inside and point down towards the ground, you can make the suspension softer AND reduce camber change. The softer ride allows the wheel to follow the road better improving grip and creature comforts.

I am just starting to understand the relationships between roll centers, roll stiffness, camber change, etc. But I am really sure that parallel links are not the be all / end all suspension solution ( because of the body roll problem )

Stingy74

This is how it was before the six link. Look at the wear pattern on the tire. There must have been 2 degrees negetive change or more! It's not like that anymore, with parallel equal length upper rods. My intention was to have a good hard and full contact patch for straight line traction, ie: drag racing. But's that's not all I do. I can't begin to explain how it improved handling. In the original 6 link article wrote over 10 years ago the guys explained the 6 link as letting you control the car. Drive it with the gas, brakes, or steering wheel. Recovery from driver error is phenominal, and I can attest to that. I chalk my tires every run and sometimes use a friends infrared heat meter and the temperatures stay stable across the entire width of the tire. Playing with tire pressures can play a great deal too.

I clipped this from the original article. Allthough I am not too concerned about toe change because I enjoy the drags better, the six link can be setup for any desired toe change to massage the car from understeer to oversteer or neutral. Mine is setup somewhere in the middle.


[Modified by Stingy74, 1:30 PM 1/18/2002]

dladd74roadster

Keith,

I agree with you about the body roll. I also agree with you about the links not having to be equal length. BUT for the purposes of someone who is going to do this themselves at home without sophisticated tools, it is by far the safest way to ensure that it will work. Granted you can move the location of the upper link down closer to the inside mounting point of the lower link and that will help minimize the effects of body roll and will also result in the upper link being longer if the inside mounting points remain in the same vertical plane but this would be more involved than engineering a 6 link at home and having good results. My Vette doesn't have enough body roll that I would consider this. As for the unequal length links, you could move inside links outward and use shorter rods on the top and it would infact accomplish the desired result. I was just trying to keep it simple and functional.

dl

427V8

Oh now what fun is that!

Very :cool:, I'm getting the feeling that doing 6 months more of research and testing would probably make an almost noticeable improvement! :lol: :lol:

dladd74roadster

Keith,

One other thing, using your example. If you have equal length uppers and lowers but have them angled toward each other at their inner mounting points. (ie not parallel but converging toward the carrier) I don't quite agree with this. (if I am understanding the example correctly. You are saying that the upper/outer mount is higher than the upper/inner mount and that the lower/outer mount is lower than the lower/inner mount.) If that is correct, wouldn't you have camber change with wheel travel?? As the wheel moves up for instance, the upper link would in effect get shorter pulling the top of the trailing arm inward, and the lower link would in effect get longer pushing the bottom of the trailing arm outward. This would cause negative camber. Am I missing something?

dl

p.s. I am really enjoying bouncing this around. :D


[Modified by dladd74roadster, 1:51 PM 1/18/2002]

Brutus

I'm certainly not going to enter into the whys and wherefors of suspension and handling principals, but I am gald to see some positive contribution towards measurements that I can follow. Thanks Norval and Stingy.
I have a new Vette Brakes Smart Strut set up ready to go in so basically to start with I have to duplicate the lower strut rod lengths for the top ones. So far so good.
The trailing arm mount should be fairly straight forward it's now a matter of working out the inner mount position and whether to go with a plate or to directly weld it to the cross member. Any further help there would be greatly appreciated. Thanks guys.

427V8

dladd
No you've got it right ( as far as I understand :) )
And I LIKE to do things as good as I possibly can, as long as I'm having fun :D:D

Below are three pictures. What they call the 'Reaction point' is what I've mistakenly called the 'roll center' when I ment the 'Instantaneous center' which is the imaginary point about where the wheel pivots as it moves up and down

As you can see in the pictures, the wheel on top will pivot about a point towards the middle of the car, the wheel on the bottom will actually pivot about a point away from the car and the wheel in the center will go straight up and down.


The question is; what happens when the car goes through a corner and the body ( and thus the inner pivots ) rotate about center of the car.
Since the car rolls away from the corner the upper controll rod gets pushed out and the lower one pushed in causing a positive camber change.

The the wheel has a negative camber change through motion, then with body roll the camber changes SHOULD cancel each other??

And yes I think this is :cool: poopie too!


[Modified by 427V8, 9:12 PM 1/18/2002]