Need some front geometry help...

[JustJohn]

I've got my car down to the frame and decided to work on front end setup before I send it out for sandblasting. I've resigned myself to probably having some custom pieces cut in the shop, but since I'm at this point, I'd like to make it better. I have the springs out and the frame set at my finished ride height but already some things just don't look right. At the moment, I just need some help figuring out where I'm at and then what to change.

[JustJohn]

So let's try another approach on this question... I was initially overwhelmed trying to process the amount of information I need to gather.
I'm starting out basic by looking at the front and rear roll centers. What stands out to me is that the drag link is not parallel to anything and every suspension model I've seen assumes this.
As a first step, I can move the idler arm down to make everything parallel.

Thoughts on this?

Added the dimensions. The wonders of a surface pro.
173956

[JustJohn]

So I'll keep adding detail until someone can provide some input. Finally got the front mounting points measure well enough that I'm satisfied it matches the CAD model. A 60's GM so there's some bump steer but I have room to move on that. Right now assuming I'll be moving the idler to get the center link parallel.
Here's the model of how it current is:
174019
This is basic software but I'm looking at about 0.5" total toe change at 2" of total suspension travel. Toe out under compression and toe in under extension.
Wheel offset is probably still a bit off but not the most critical thing right now.

[stab6902]

It's a little tough to tell based on that one picture, but that's a 1st gen Camaro subframe, right?

Regardless, I like to see the center link parallel to the ground / rest of the car, and the idler and pitman arms as close to the same length as possible. You'd think that would always be the case, but I've seen lots of weird combinations - probably from people mixing and matching parts that fit but aren't correct.

[stab6902]

Looking at that frame pic again it might be for a big car - maybe the Impala in your signature pic?

[JustJohn]

Ryan - thanks. It is for my 69 Impala. Hard to get off the shelf parts but that's ok for now. Just looking at bump steer, I can get a lot of improvement bringing the outer tie rods up an inch. Problem with that is 2" is more realistic just using a commercially available adjustment kit so I'm looking at custom steering arms. Not that big of a deal, I can have them made here at work. This is a plot of the changes over 6" of total travel at stock, 1", and 2" out tie rod vertical change:
174027

[JustJohn]

It's a little tough to tell based on that one picture, but that's a 1st gen Camaro subframe, right?

Regardless, I like to see the center link parallel to the ground / rest of the car, and the idler and pitman arms as close to the same length as possible. You'd think that would always be the case, but I've seen lots of weird combinations - probably from people mixing and matching parts that fit but aren't correct.

The idler and pitman arms seem to be the same length, I can confirm the measurements. They're supposed to be correct for the car. The easiest way to get the center link parallel to the ground is to move the idler arm down. I can do it with new holes in the frame or cutting a new piece from from billet. That was a basic assumption I already worked into my model.

[stab6902]

Sweet car! Your ride height measurements look a little high compared to the B-bodies I've had. The rule of thumb is that the lower A-arm pivot points (bushings and ball joint) should be "level" with the ground, which helps with camber gain. Make sure you have your ride height nailed down before you make any other changes.

You may also find this tool helpful if you haven't seen it already:
http://vsusp.com/?tool=2d#0.8%26project_name%3A67-69%20Factory%20Suspension%26trim%7Bbody_roll_angle %3A0%7Cfront.left_bump%3A0%7Crear.left_bump%3A0%7C front.right_bump%3A0%7Crear.right_bump%3A0%7D%26fr ont%7Bframe.susp_type%3A0%7Cframe.bottom_y%3A19050 %7Cframe.center_to_upper_mount_x%3A36576%7Cframe.b ottom_to_upper_mount_y%3A28575%7Cframe.center_to_l ower_mount_x%3A28486%7Cframe.bottom_to_lower_mount _y%3A3175%7Ccontrol_arms.upper_length%3A23495%7Cco ntrol_arms.lower_length%3A36283%7Cknuckles.hub_to_ upper_x%3A14604%7Cknuckles.hub_to_lower_x%3A10160% 7Cknuckles.hub_to_lower_y%3A5080%7Cknuckles.hub_to _upper_y%3A15875%7Cknuckles.hub_to_strut_axis%3A14 000%7Cknuckles.strut_incl%3A8000%7Csteering.active %3A0%7Csteering.hub_to_outer_tie_rod_x%3A7620%7Cst eering.hub_to_outer_tie_rod_y%3A7620%7Cwheels.offs et%3A4000%7Cwheels.diameter%3A1700%7Cwheels.diamet er_expl%3A35000%7Ctires.size_convention%3A0%7Ctire s.section_width%3A24500%7Ctires.aspect_ratio%3A400 0%7Ctires.diameter_expl%3A50000%7Ctires.width_expl %3A7620%7Ctires.compression%3A0%7D%26rear%7Bframe. susp_type%3A0%7Cframe.bottom_y%3A9200%7Cframe.cent er_to_upper_mount_x%3A28500%7Cframe.bottom_to_uppe r_mount_y%3A24000%7Cframe.center_to_lower_mount_x% 3A17000%7Cframe.bottom_to_lower_mount_y%3A2400%7Cc ontrol_arms.upper_length%3A24800%7Ccontrol_arms.lo wer_length%3A37500%7Cknuckles.hub_to_upper_x%3A150 00%7Cknuckles.hub_to_lower_x%3A13000%7Cknuckles.hu b_to_lower_y%3A13000%7Cknuckles.hub_to_upper_y%3A1 3000%7Cknuckles.hub_to_strut_axis%3A14000%7Cknuckl es.strut_incl%3A8000%7Csteering.active%3A0%7Csteer ing.hub_to_outer_tie_rod_x%3A7620%7Csteering.hub_t o_outer_tie_rod_y%3A7620%7Cwheels.offset%3A4000%7C wheels.diameter%3A1500%7Cwheels.diameter_expl%3A35 000%7Ctires.size_convention%3A0%7Ctires.section_wi dth%3A19500%7Ctires.aspect_ratio%3A4500%7Ctires.di ameter_expl%3A50000%7Ctires.width_expl%3A7620%7Cti res.compression%3A0%7D%26pref%7Bdiag1.px_per_mm%3A 200%7Cdiag1.front_or_rear%3Afront%7Ctab.active%3A2 %7Cunits%3A0%7Cshow.f%3A1%7Cshow.ca%3A1%7Cshow.k%3 A1%7Cshow.st%3A1%7Cshow.stl%3A1%7Cshow.w%3A1%7Csho w.t%3A0%7Cshow.rc%3A1%7Cshow.rcl%3A1%7Cshow.ic%3A1 %7Cshow.icl%3A1%7Cshow.fvsa%3A0%7Cshow.tl%3A0%7Csh ow.kpil%3A0%7Credraw_during_drag%3A1%7Cchart.x_axi s_center%3A0%7Cchart.x_axis_window%3A10%7Cchart.x_ axis_num_steps%3A21%7Cchart.x_axis_field%3Atrim.bo dy_roll_angle%7Cchart.y_axis_fields%3A%5BFR%5D.gen eral.roll_center.y%7D

[JustJohn]

Thanks for the suspension tool. I actually have the springs out of the car and it is sitting at ride height, ~ 2" lower than stock. What you are not seeing is the frame member below the control arm mounting point. I have a little room there but want to keep the option to drive over speed bumps. Also don't have "true" lower A-arms. It's closer to a Ford with strut reaction rods, which gives me an odd lower ball joint that does not have any options to change.


Sweet car! Your ride height measurements look a little high compared to the B-bodies I've had. The rule of thumb is that the lower A-arm pivot points (bushings and ball joint) should be "level" with the ground, which helps with camber gain. Make sure you have your ride height nailed down before you make any other changes.

You may also find this tool helpful if you haven't seen it already:
http://vsusp.com/?tool=2d#0.8%26project_name%3A67-69%20Factory%20Suspension%26trim%7Bbody_roll_angle %3A0%7Cfront.left_bump%3A0%7Crear.left_bump%3A0%7C front.right_bump%3A0%7Crear.right_bump%3A0%7D%26fr ont%7Bframe.susp_type%3A0%7Cframe.bottom_y%3A19050 %7Cframe.center_to_upper_mount_x%3A36576%7Cframe.b ottom_to_upper_mount_y%3A28575%7Cframe.center_to_l ower_mount_x%3A28486%7Cframe.bottom_to_lower_mount _y%3A3175%7Ccontrol_arms.upper_length%3A23495%7Cco ntrol_arms.lower_length%3A36283%7Cknuckles.hub_to_ upper_x%3A14604%7Cknuckles.hub_to_lower_x%3A10160% 7Cknuckles.hub_to_lower_y%3A5080%7Cknuckles.hub_to _upper_y%3A15875%7Cknuckles.hub_to_strut_axis%3A14 000%7Cknuckles.strut_incl%3A8000%7Csteering.active %3A0%7Csteering.hub_to_outer_tie_rod_x%3A7620%7Cst eering.hub_to_outer_tie_rod_y%3A7620%7Cwheels.offs et%3A4000%7Cwheels.diameter%3A1700%7Cwheels.diamet er_expl%3A35000%7Ctires.size_convention%3A0%7Ctire s.section_width%3A24500%7Ctires.aspect_ratio%3A400 0%7Ctires.diameter_expl%3A50000%7Ctires.width_expl %3A7620%7Ctires.compression%3A0%7D%26rear%7Bframe. susp_type%3A0%7Cframe.bottom_y%3A9200%7Cframe.cent er_to_upper_mount_x%3A28500%7Cframe.bottom_to_uppe r_mount_y%3A24000%7Cframe.center_to_lower_mount_x% 3A17000%7Cframe.bottom_to_lower_mount_y%3A2400%7Cc ontrol_arms.upper_length%3A24800%7Ccontrol_arms.lo wer_length%3A37500%7Cknuckles.hub_to_upper_x%3A150 00%7Cknuckles.hub_to_lower_x%3A13000%7Cknuckles.hu b_to_lower_y%3A13000%7Cknuckles.hub_to_upper_y%3A1 3000%7Cknuckles.hub_to_strut_axis%3A14000%7Cknuckl es.strut_incl%3A8000%7Csteering.active%3A0%7Csteer ing.hub_to_outer_tie_rod_x%3A7620%7Csteering.hub_t o_outer_tie_rod_y%3A7620%7Cwheels.offset%3A4000%7C wheels.diameter%3A1500%7Cwheels.diameter_expl%3A35 000%7Ctires.size_convention%3A0%7Ctires.section_wi dth%3A19500%7Ctires.aspect_ratio%3A4500%7Ctires.di ameter_expl%3A50000%7Ctires.width_expl%3A7620%7Cti res.compression%3A0%7D%26pref%7Bdiag1.px_per_mm%3A 200%7Cdiag1.front_or_rear%3Afront%7Ctab.active%3A2 %7Cunits%3A0%7Cshow.f%3A1%7Cshow.ca%3A1%7Cshow.k%3 A1%7Cshow.st%3A1%7Cshow.stl%3A1%7Cshow.w%3A1%7Csho w.t%3A0%7Cshow.rc%3A1%7Cshow.rcl%3A1%7Cshow.ic%3A1 %7Cshow.icl%3A1%7Cshow.fvsa%3A0%7Cshow.tl%3A0%7Csh ow.kpil%3A0%7Credraw_during_drag%3A1%7Cchart.x_axi s_center%3A0%7Cchart.x_axis_window%3A10%7Cchart.x_ axis_num_steps%3A21%7Cchart.x_axis_field%3Atrim.bo dy_roll_angle%7Cchart.y_axis_fields%3A%5BFR%5D.gen eral.roll_center.y%7D

[JustJohn]

Little bit of model refinement based on re-checking my measurements, which will probably happen a couple more times... I'm not building a race car here so the end goal is improvement, not perfection. That being said, only leveling the center link might be my best option. Toe change in compression is not terrible.
174100

[JustJohn]

And this continues to spiral...
Pitman and idler arms are different lengths (6" and 5.5"). I replaced everything with new parts a couple of years ago so its "correct" for the car. The center link is not parallel with either the frame or the ground. The best information I have is the factory assembly manual drawings, which clearly shows everything parallel but no dimensions. Could use some help with the consequences of squaring everything up. Here's the linkage from the top. String lines are parallel to the frame.174111

[stab6902]

I had the exact same issue several years ago when I replaced the center link and idler arm on my 1994 Fleetwood. If memory serves, I used Moog parts, which were the right part numbers for the car, but slightly different from original equipment. A quarter to a half inch difference here and there makes a huge impact on the geometry. I had to change the length of the passenger side tie rod assembly a lot to get the car to go straight down the road, and the ackerman was all jacked up because the tires squealed in sharp parking lot turns, which it never did before.

It was a high mileage daily driver so I lived with it, but it always bothered me. Let us know if you're able to find a brand of parts that fit right. I think the problem is partially sloppy quality control from the aftermarket and partially them trying to minimize the number of part numbers; as long as it bolts on and functions, they call it good enough, rather than really trying to duplicate all the subtle differences between model years and configurations.

[JustJohn]

I actually work for an aftermarket parts company so I can tell you exactly how it works...

You get pretty good fit and function up to about a 20 year old application but by that time there have been some consolidations to cover very low volume part numbers. After that, we're looking at vehicles that usually aren't classics, just old and still in service. New engineers consolidate down again without really understanding the application and you get a part that basically just installs in the hole but maybe doesn't work as well. Then the company gets bought and somebody eventually reproduces the part as another consolidation but based on the last available aftermarket part because they couldn't get an OE version. Kind of sucks but that's how it goes.


I had the exact same issue several years ago when I replaced the center link and idler arm on my 1994 Fleetwood. If memory serves, I used Moog parts, which were the right part numbers for the car, but slightly different from original equipment. A quarter to a half inch difference here and there makes a huge impact on the geometry. I had to change the length of the passenger side tie rod assembly a lot to get the car to go straight down the road, and the ackerman was all jacked up because the tires squealed in sharp parking lot turns, which it never did before.

It was a high mileage daily driver so I lived with it, but it always bothered me. Let us know if you're able to find a brand of parts that fit right. I think the problem is partially sloppy quality control from the aftermarket and partially them trying to minimize the number of part numbers; as long as it bolts on and functions, they call it good enough, rather than really trying to duplicate all the subtle differences between model years and configurations.

[stab6902]

Thanks for the first hand insight. It's a bummer but I get it. I guess I'd rather have a "close enough" replacement part than none at all, but it's frustrating if you're detail oriented and want everything to be "right."