84-87 vs 88 front suspension (Page 7/10)
mender NOV 26, 01:31 AM

quote
Originally posted by pmbrunelle:

Did you do the spherical bearing mod to the front wishbones as well?

Actually, from the factory, the pivots didn't line up...


Haven't yet but will be doing that. Mine presently have poly and I can feel the resistance because of the misaligned axes.

I just got the car on the hoist and leveled with the springs out and sway bars disconnected to do the suspension measurements. Did the rear camber curves and bumpsteer and will be doing the front next.
cvxjet NOV 26, 01:40 PM
I wanted to chime in here with my 1 cent opinion (That's probably all it's worth!)

The difference between the REAR 84-87 vs 88 is huge- big benefit to change over...The front is just not that big...Pontiac could have saved a lot of money by making a stand-alone separate hub with less offset (Bring the mounting flange in say a full inch, which, with the added bolt-on disc thickness, would have improved scrub radius by almost 3/4")......The other thing would be to simply mount the inner A-arm mounts in different locations to improve the geometry.....Somewhat like what Mender is doing.

I grew up with Ford/Mustang cars, so I knew about the "Shelby mod" to the front of first-gen mustangs; Pull the upper a-arm out and re-drill the mounting holes one inch lower, so that you get better camber gain during suspension deflection....Also, there is benefit from a lower roll center......On the Mustangs it's simply drilling holes, but on the Fiero, the mounting tube sits on top of the subframe/Spring-perch....A future project of mine is to drill thru the subframe and weld a new mounting tube below the spring perch (Basically resting on it from underneath, lowering the mounting point one inch....I have a spare subframe, so I just have to find the time.....Once I finish it, I will let everyone know how it turned out....(I want to align everything properly, so I am thinking of using angle-iron bars, with alignment tubes welded on, then mount one end in the original position on one side, and then use the far end to align the new hole/tube on the other side, then reverse the process to finish the first side)(Obviously, this fixture will allow the job to be repeated...)
pmbrunelle MAR 26, 08:32 PM

quote
Originally posted by mender:
I'm going through my front suspension on my '87 GT to optimize the geometry for racing. My mod for anti-dive is a lot simpler, just involves slotting the lower control arm pivot points to move the front of the arm down and the rear of the arm up. No change in caster and the anti-dive went up to about 30%.



Any more feedback about this five years later?

Did you leave the steering rack at the in the stock position on the crossmember, or did you move it down a bit to follow the front LCA pivot?
Will MAR 30, 09:20 AM

quote
Originally posted by mender:

I'm going through my front suspension on my '87 GT to optimize the geometry for racing. My mod for anti-dive is a lot simpler, just involves slotting the lower control arm pivot points to move the front of the arm down and the rear of the arm up. No change in caster and the anti-dive went up to about 30%.

Big improvement under braking; before the tires would tuck up into the wheel wells enough to rub through the plastic fender liners. The camber change in the last bit of compression was excessive enough to cause the fronts to wash out. Now with the anti-dive the nose only drops about 1 1/2" despite the sticky tires and hard braking. Tire wear is much better as well.

I've moved the upper ball joint to get the static camber that I want. I'm going to move it back to get more caster, then weld in a plate to reinforce the control arm. Final step will be to move the rack to minimize the bumpsteer that will result from the geometry changes.





quote
Originally posted by pmbrunelle:

Any more feedback about this five years later?

Did you leave the steering rack at the in the stock position on the crossmember, or did you move it down a bit to follow the front LCA pivot?




Building wedge-shaped spacers that rotate the entire front suspension around the lower control arm rear pivot was the proof of concept that showed that brake dive could be eliminated. That first method had the aforementioned drawbacks.

Like Mender, I've been thinking that just raising the rear pivot without spacing the crossmember may get most of the way there without the additional problems.

Lowering the LCA forward pivot without also moving the rack would definitely cause bump steer. Moving the LCA rear pivot up may also cause bump steer, as it rotates the plane of the LCA so that the inner tie rod end moves "up" (further from the plane), even though the inner tie rod end itself does not move.

However, the LCA forward pivot is pretty close to the wheel centerline, so the projection of steering components into the vertical transverse plane at the front wheel centerline wouldn't move around much.

[This message has been edited by Will (edited 03-30-2022).]

pmbrunelle MAR 30, 12:53 PM

quote
Originally posted by Will:
Building wedge-shaped spacers that rotate the entire front suspension around the lower control arm rear pivot was the proof of concept that showed that brake dive could be eliminated. That first method had the aforementioned drawbacks.

Like Mender, I've been thinking that just raising the rear pivot without spacing the crossmember may get most of the way there without the additional problems.

Lowering the LCA forward pivot without also moving the rack would definitely cause bump steer. Moving the LCA rear pivot up may also cause bump steer, as it rotates the plane of the LCA so that the inner tie rod end moves "up" (further from the plane), even though the inner tie rod end itself does not move.

However, the LCA forward pivot is pretty close to the wheel centerline, so the projection of steering components into the vertical transverse plane at the front wheel centerline wouldn't move around much.



I'm leaning towards doing the mender mod now.

Stock, the Fiero/Chevette knuckle seems not too bad, in the sense that the tie-rod-ball is pretty down low, perhaps almost in the LCA plane (plane defined by pivots + ball joint).

So I might move the rack downwards by the distance equal to the change in LCA plane height, evaluated at the position of the tie-rod ball. Or something like that... I am imagining new steel rack-to-crossmember brackets, welded on.

I suppose that I also want the steering column to penetrate the "firewall" at the same position as stock, so that the weather sealing boot works correctly.

To keep the same firewall penetration point with a lowered steering rack, the steering rack shall be slightly tilted forwards in the pitch axis.

This will affect the lower U-joint angle, but I think it should be workable, in terms of the U-joint ratio variation.

I still have your spherical bearing kit for the LCA sitting in a box, but it only makes sense to tack (and fully weld) the parts in place once I have determined the new LCA pivot positions.
zkhennings MAR 31, 05:42 PM
I too am going to try and achieve this by lowering the front mounting holes at a ratio to what I raise the rear mounting holes that hopefully keeps the axis of rotation of the LCA the same distance from the inner tie rod. I'll have to do some maths. I am also planning to weld a plate onto the front crossmember to make mounting locations for the upper control arm that are lower down and probably towards the rear of the car to add a little caster. Might add mounting provisions for a coilover into this plate as well. I plan to make front lower and upper control arms with heim joints, and I could make them slightly longer so I could run a wheel with a little more offset and get a smaller scrub radius without having the front end look really narrow. I could be wrong, but it doesn't seem beneficial to have a higher kingpin angle if you can run a wheel with less offset.

I will still probably have to play with steering rack position, but I would like to measure everything and put it all in CAD and see. Have to make some kind of jig to give me a good datum to measure to.

I currently run 88GT wheels on my 85, and the reduced scrub is noticeable, I do have grand am rotors though so I am not sure if I am back where I started even with the additional offset of the wheel.
ericjon262 MAR 31, 11:01 PM
my current setup: Koni reds, stock 1985 SE springs (F41 package), Will's Anti dive setup, Addco heavy duty front swaybar, Spherical bearing LCA's, 2" belltech drop spindles, stock UCA with poly bushings, in the rear, I have a 1988 cradle, KYB struts, coilovers, and rod end lateral links.

having installed and driven Will's anti-dive setup, I will make the following installation comments:

rotating the crossmember forward 6 degrees is a little more involved than that sounds, I did this mod, and installed spherical bearings in the LCA's, at the same time, the spherical bearings have no give, when I put the control arms back on, they didn't quite line up. as rotating the crossmember moved the control arm mounts slightly closer together. I had to slot the bolts in the crossmember, and slide it forward a bit to make everything fit.

Not sure if it's been mentioned here yet or not, but the steering shaft just barely still fits

This mod lifts the front of the car, I installed drop spindles at the same time to minimize the lift. drop spindles and factory spindles are not all equal, stock brakes may not be a problem, custom brake setups like the C5 fronts I have on my car, may no longer bolt on in the same manner, and may require shimming to align the caliper to the rotor. eventually, I will make my own spindles to eliminate the shims I needed to install to gain alignment.

the front braces on the crossmember are not long enough to meet the crossmember, they need to be lengthened to fit.

Shocks no longer meet the control arm at the same angle, I found it easier to install the shock on the car, then bolt the shock to the control arm, then the control arm on the car, your results may vary.

don't break any of the bolts holding the crossmember to the frame... it's a PITA to fix them.
Now, Driving comments:

the car stops dead flat, it's pretty nice, and so far, very predictable, that said, I have not attempted to hammer the brakes hard enough to induce lockup, but I have braked fairly aggressively several times, and each time was very predictable and flat.

the biggest con, right now as mentioned above, doing nothing else, rotating the crossmember eliminates all of your caster. the car now has a tendency to wander, and follow ruts in the road a bit. custom upper control arms should solve that problem, but are another feature that needs to be addressed, similar to the drop spindles minimizing lift.

without custom upper control arms restoring caster, and 2" drop spindles. the tires are also SUPER close to the wheel well liners and do occasionally contact them.


Overall, I like it, but I definitely need to gain more caster, my 3/4 ton truck feels more stable, if I end up with another 84-87 car, I'll do it again, but I may go about it in other ways, like raising the rear LCA point.

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"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper

zkhennings APR 01, 11:03 AM
Has the anti-dive had an effect on the nose of the car raising under acceleration? I imagine that it has stayed relatively the same?

My thoughts being that while the front wheels during braking are putting a lot of force on the control arms which are being "pulled" to the rear of the car (imagining forces at the ball joints), and with stock pro-dive geometry as the control arms travel rearwards, they also travel up due to the angle of the control arm.

With my WRX, people install an "anti lift kit" which is basically a pro-dive kit by dropping the rear pivot of the front control arm. This makes the car pitch more on braking, but during accelerating the forces of the front wheels pulling the control arm forwards forces the wheel into the ground giving more traction on corner exit.

However during accelerating with a RWD car the wheels are not applying much force at all to the control arms. The Fiero front wheels if anything are applying an extremely mild "braking" force to the front control arms which would actually make it lift less during acceleration. But I imagine it is relatively negligible and the anti-dive change has not really affected the lift of the front end, but would not do anything to improve it.

Is the only way to really control front end lift under acceleration with stiffer shorter springs that do not compress as much as therefore do not extend as far under accelerating?
pmbrunelle APR 01, 12:14 PM
Anti-dive describes how the suspension reacts during braking, when the road pushes rearwards on the contact patch.

During acceleration, unless your foot is on the brake pedal, the front wheels on a Fiero are just rolling along for the ride. Anti-dive doesn't play a part here.

Yeah, you need stiffer front springs to reduce the front-end lift during acceleration. That's just the result of weight transfer.

Part of the motorboat feeling though comes from the pro-squat in the rear of stock 84-87 Fieros, so you may want to work on an anti-squat mod in the rear. It's on my agenda, but not for a while...
ericjon262 APR 01, 01:34 PM

quote
Originally posted by zkhennings:

Has the anti-dive had an effect on the nose of the car raising under acceleration? I imagine that it has stayed relatively the same?

My thoughts being that while the front wheels during braking are putting a lot of force on the control arms which are being "pulled" to the rear of the car (imagining forces at the ball joints), and with stock pro-dive geometry as the control arms travel rearwards, they also travel up due to the angle of the control arm.

With my WRX, people install an "anti lift kit" which is basically a pro-dive kit by dropping the rear pivot of the front control arm. This makes the car pitch more on braking, but during accelerating the forces of the front wheels pulling the control arm forwards forces the wheel into the ground giving more traction on corner exit.

However during accelerating with a RWD car the wheels are not applying much force at all to the control arms. The Fiero front wheels if anything are applying an extremely mild "braking" force to the front control arms which would actually make it lift less during acceleration. But I imagine it is relatively negligible and the anti-dive change has not really affected the lift of the front end, but would not do anything to improve it.

Is the only way to really control front end lift under acceleration with stiffer shorter springs that do not compress as much as therefore do not extend as far under accelerating?



it stays flat as Patrick said, the fronts are just rolling at that point unless you're inputting force some other way, braking, driving the front wheels, ect. the rear squatting could give the impression of front end lift though.

in this clip, I hit it from about 15-80, you can see there's pretty much no rise from the nose of the car.

https://youtu.be/60SUceya6Y4

------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper