This weekend I finished the coil overs but before I put the tires and springs on I decide to check the toe change through suspension travel.
To do it properly I have to mount a large aluminum plate in place of the tire. The plate is 27 inches wide by 12 inches high and it fits over the studs. The first problem I had was the caliper was already mounted , bled and I didn;t want to remove it and have to rebleed so I found a bunch of 1/2 inch fine nuts, my studs are upgraded to 1/2 inch and run double sets over all the studs. They acted as spacers and allowed the plate to be bolted on the hub.
I then positon the bump gage which consists of a rigid frame, a wheel that rides on the rear end of the plate and a dial gage that rides on the front end, this saves subtracting one dial gage from another. Toe is a simple one reading from the dial gage.
The last thing is a jack to move the suspension up and down.
This is the readings I found 1/2 inch up .006, 1 inch up .040 and 2 inches up .200. All toe outs and that is per wheel.
Dropping the suspension I got 1 inch down .075 and 2 inches down .150 again toe out.
This is more then I hoped for but I will live with it. Camber like before stayed at 1/2 degree maximum change from full droop to fully compressed.
I then installed the springs over the shocks, set the car down and adjusted the ride height with the little wrench that turns the nut on the shocks.
The rear is done for now and I will start on the front end this week.

 

Wow thatsa lotta toe change!

Maybe next winter I'll have to work on the rear end...

 

I was just on the phoh VBP about their rear strut package and much other stuff, and shocks too....I asked about the lower strut bracket they offer, as I have the rods allready with what I think is a stock '72 bracket...they say the differances are theirs is adjustable for height, and so I asked wether to raise or lower the bracket I have, they said lower about an inch or 1.5 inches, I forget exactly....at any rate, that would require my re aligning the rear, something I don't want to get into just now....but he did say with their setup there about zero variation was possible in camber, but I don't recall anything about toe being commented on....
it was a wide ranging discussion based on my getting their latest catalogue.....

GENE

 

My inner lower strut mounting location is dropped about the same and I have a maximum of 1/2 degree camber change from full droop to full compression. Camber is not a problem. It is the toe change.
While this seems alot check out a stock front end. The new well 2002 mustang that I checked for toe change had 3/4 inch toe in on 3 inches rise. That is more then my rear end.
For now I will live with the toe change in the rear but if a better idea came along I would look at it but not something that involves cutting the battery boxes, frame modifications don't bother me but cutting the fiberglass does.
I think the front bump steer is far more critical then the rear.

 

Norval I think you have a great approach to the 6 link, did you make the top and bottom link the same length?

I have been considering building a 6 link if nothing else but to stop the side yoke wear, but I wonder what you would think if a person was to make the lower link as long as possible , attaching it under the center of the rear end which should further decrease toe out on compression.

What do you think the down side would be of building longer lower link other than increasing camber on compression? SSS

 

I've been following this discussion for a while and spending quite a bit of think time on the subject lately. I do not think it is possible to ever get zero toe change and zero camber change from a trailing-arm-type suspension. There's always going to be a trade-off of one for the other. Parallel equal-length strut rods will yield zero camber change, but as the strut rods move up or down, they are going to pull the trailing arm inwards and cause toe-out. The only way I can see to lessen toe out is to make the strut rods as long as possible so the arc is larger.
Toe change can be minimized with a non-parallel, non-equal-length strut rod configuration with one strut rod low in it's arc and the other high. As the suspension is moved, one strut rod is pushing while the other is pulling. Of course this will twist the trailing arm, causing camber change... and who knows how long the trailing arm bushing will last with that kind of twisting going on.
I'm heading towards the latter as my goals are more oriented on handling and road courses. Camber change will help keep the tires planted in the turns.
I have done some experimenting to verify this with a demo version of Suspension Analzyer 1.1, but I don't have any solid measurements to start from until I get my vette back from the paint shop. Would anyone happen to have some rear suspension measurements I can plug in? I need the distance from the wheel centerline to trailing arm pivot, trailing arm pivot to vehicle centerline, lower strut rod pivot to trailing arm pivot, strut rod pivot to vehicle centerline...
-Jason

 

You CAN get 0 toe change if you use a double a arm suspension like the C5 has.
Toe can also be controlled very good with a system like the guldstrand system or like the greenwood & C4 system. The trailing arms must have 2 pivot points in them so that they have no influence on toe. The longer these trailing arms, the better indeed but not because of toe change but because of movement of the hub assembly fore and aft.
When you use a setup like the guldstrand one the 2 rods control camber and toe. It might be nice to add one more rod like the 6 link so that the camber is controlled by the rods only and not the 1/2 shafts. Then the toe can still be controlled by the setting of the 2 lower rods.





[Modified by Twin_Turbo, 6:45 AM 11/25/2003]

 

silverslashstreak. The top and bottom links are not the same length. The bottom is longer and is stock length, the top is 13.5 center to center of the heim joints so a connecting link of 10 or 11 inches is used along with 5/8th left and right heim joints.

I also agree with makeing the links as long as possible but if you made the lower one longer the arc of it's travel would hit the exhuast pipe.
I am getting a digital camera this christmas so I will be able to post pictures but our lower link is already as long as possible and clear the exhuast.
With side pipes it is not an issue.
Also the top could be made really long, well either cross the opposite one or have a center take off but the pivot points are important and the yoke dictates this.
I really like the system because the yokes are no longer bumping the pin, I shorten them back to the C clip groove and the adjustability is great, No more front toe shims. I can also change the track width by about 1/2 inch per side by shimming the front of the trailing arm on one side then using the 6 link strut rods to move the back around.
Last night I finished totally the back and started on the front.
Between the 6 link and the coil overs on the back it is totally adjustable for height, camber and toe. Also looks really clean back there.

 

blue72 I agree the strut rods should be longer but it is almost physically impossible to do without side mount exhaust and I don't want my exhaust dumping beside my ear.
Our normal 6 link solves the camber change problem and yoke wearing on the pin plus easy adjustments.
Toe is the problem and for now I will live with it.

 

Twin Turbo if I knew how to build a good rear system I would build it but our battery box is right in the way for just about anything. There is just no room without cutting. Cutting the frame bothers me less then the fiberglass.

 

Oh, I have no problem whatsoever with cutting the battery box

 

solution would be a hybrid system of the greenwood and guldstrand.

You need a 3rd link to form a triangle to the diff to control toe. either make a link go from the center of the diff to the rear of the T-arm assy as done in the C4 or use two lower strut rods spaced far enough apart as is done with the Gulstrand kit.

Once you have done this the only forward link required is fro fore and aft location. The T-arm needs to pivot for toe near the spindle assy. Either use two links link the C4 or after market systems or modify the old T-arm to pivot.

Dave

 

I wonder...the Guldstrand system uses the longest possible trailing links, I assume to minimize the fore/aft movement (and possibly toe) of the wheel during jounce/rebound, but the trailing links on the C4 are really short, as are the trailing links on the Greenwood system. Why didn't GM make the links longer on the C4? They could have been designed to attach somewhere behind the halfshaft like Guldstrand did, but instead they attach forward of the halfshaft, making the links very short.

Anyone care to prognosticate on which is more advantageous?

Chris

 

I would suspect that the longer the trailing links are and the point at which they would theortically intersect ( most forward position the best) would tend to reduce squat on acceleration and may also improve when hop reduction.

Need a chassis person to answer that one.

 

I was thinking about something like that too, IMO the best solution would be the guldstrand system with it's nice long trailing arms, the 2 lower arms for camber and toe and one upper arm like the 6 link as the upper camber rod and that way eliminating the 1/2 shaft as a suspension geometry member.

You would need 2 trailing arms to control a twisting of the hub assemble that would screw up the camber and toe settings. The only other way to eliinate it is to triangle the upper members, so in essece an a arm setup. 2 parrallel rods like the guldstrand would work on the bottom for toe and camber control.

Th intersection point of the 2 trailing arms indeed function as a longer virtual trailing arm. Also, the individual angles and moubnting points allow precise "setting" of the virtual hinge point, much in the same was as the IC on A-arm suspensions. Now, what would be the ideal virtual arm length? We'd probably need a suspension program to work that out. I can't give any good argumented idea for it.


[Modified by Twin_Turbo, 3:19 PM 11/25/2003]

 

Never thought about the advantage of changing the width of track out back but that would be nice adjustment. but like you pointed out the side yoke wear (i am on my third set) problem would make the six link worth it alone. Because the side yokes start wearing right away and continue to get looser. the longer you drive.

This is a little off the subject, but after years of blaming the rear end , when I finally found a great integrated power steering box , the car drives so good I have almost forgotten about all the problems out back. 2 turns lock to lock.

I be intrested to hear how it turns out when you get the front end done.

 

Never thought about the advantage of changing the width of track out back but that would be nice adjustment

When I installed the coil overs out back the passengers side had more clearance between the arm and the fiberglass box then the drivers side. On the drivers side the coilover almost touched the trailing arm so I added an extra 1/4 inch shim to the inside of the trailing arm then moved the back of the trailing arm over to get the proper toe. It made the tires more even in the spacing in the wheel well. If you also have a slight rubbing problem on the inside of the tire it allows you to gain a little clearance.
Toe/camber adjustments are so easy.