Real Fiero Tech

After skimming through several threads written in word salad about rear bump steer, I am trying to clarify the problem and a solution. Is the bump steer issue that the tie rods and lower control arms are of unequal lengths, and due to this the toe moves slightly as the suspension travels away from the center of its range?

If so, this looks like an easy fix as shown in these two pics:



The knuckles have been swapped with each other to swap the sides that the tie rods connect to the engine cradle. This allows for easier placement of the connection point of the tie rods to the engine cradle.


This drawing keeps the knuckles in their original positions, but changes the location that the tie rod connects to the engine cradle. It shortens the length of the tie rods to match the radius/length of the lower control arms.

More discussion here:
https://ironduke7.tripod.com/bumpsteer.htm

CaptainHindsight wrote: ↑Tue Aug 24, 2021 4:07 pm

I can't speak to the particulars, of the change, but I can speak to the fitment. and this won't work on my car, and I suspect several others as well, as the inner mount occupies the same space as the transmission case on the driver's side.

The solution shown in the picture only works for the passenger side only if it clears the crank pulley.

The solution in the drawing looks like an easy fix to move the weldments for the tie rods closer to the knuckles. So easy that I wonder why Pontiac did not just do so. I'm wondering why they didn't. Then again I'm seeing all sorts of odd mashups from the factory designed during a time when CAD was in its infancy and fuel economy had become a big concern.

Pulling from your linked site:



Well... maybe that didn't work.

The pivot axis for the control arm is NOT parallel to the centerline of the car. The forward pivots for the control arms are further apart than the rear pivots. You can see that from your Stock vs Proposed top view above. The original toe link isn't awful... it just isn't great.

This is probably the best solution I've seen: https://www.fiero.com/forum/Forum2/HTML/134732.html#p26





It does mount the toe link in single shear, but since the ball joint is taking all the lateral loads, that should be ok.
I'm actually expecting to use that setup with my fabbed hub carriers, but I'll use a spacer so I don't have to cut into the cradle that way.

I just get 403 errors from your links.

Any chance you can copy that image to another image site so it may be posted here?

The first one is from your Tripod site and the last two are at the Old Europe post I linked.

Thanks.

http://www.fiero.com/forum/Forum2/HTML/134732.html#p26

Have to copy and paste the link since they have a certificate issue at that site. I also used http vs https in the address.

That is ugly. Almost makes me want to make new knuckles.

CaptainHindsight wrote: ↑Thu Aug 26, 2021 4:08 pm

That is ugly. Almost makes me want to make new knuckles.

The Dark Side of Will wrote: ↑Sun Aug 16, 2020 4:31 pm Progress on my fabricated hub carriers:

Then:

The Dark Side of Will wrote: ↑Sun Jun 23, 2019 11:48 am Initial stab at the fabbed knuckle design... lots of stuff to figure out yet, though.

Now:

If I go this route I'll probably cast and then machine.

I want to see how bad it is after all Delrin bushings, coil overs, larged dia rims and lower profile tires. It would be part of stage 2 next year for this car.

CaptainHindsight wrote: ↑Thu Aug 26, 2021 5:28 pm If I go this route I'll probably cast and then machine.

I want to see how bad it is after all Delrin bushings, coil overs, larged dia rims and lower profile tires. It would be part of stage 2 next year for this car.

whats your casting method? what are you doing for material QC? this could get tricky for parts under the amount of load that a knuckle sees.

Yeah, casting a critical part of primary structure is a whole different ball of wax than casting an intake manifold.

Sand cast iron. Sand molds are 3d printed.

Similar to:
https://youtu.be/r4bkN61WtkI

https://youtu.be/EfN6LTesvks

Might be of interest:
https://blog.foerstergroup.com/en/compo ... al-testing

I'm very familiar with the process, but how are you going to verify filing without voids/porosity? where are you acquiring material and how are you ensuring it will meat structural requirements? I'm definitely not saying don't do it, but this isn't a part you want to break going down the road.

I use local foundries for the pour. I work on the tech in the lab so I have access to all the test equipment.



Ultrasonic covers your most concern. Dye and eddy current test for the surface.

If you can use lost foam casting many of the foundries will pour for you for next to nothing if you bring in your own molds.

10-4, that makes this seem like a much more reasonable undertaking now. I was envisioning my backyard setup and cringing.

The rear 84-87 cradle and suspension is really bad. You should look into transplanting an '88 cradle and suspension. Especially if this is your daily.

ericjon262 wrote: ↑Thu Aug 26, 2021 10:28 pm 10-4, that makes this seem like a much more reasonable undertaking now. I was envisioning my backyard setup and cringing.

That little cauldron in your back yard flashed as a mental imagine for me too. Haha. Man that was a long time ago.

he rear 84-87 cradle and suspension is really bad.

What is so really bad about it? The toe changes slightly near the end if its suspension travel with the factory bushings and tie rod mounting locations.

I can argue that whole car is an under powered and twisty and needs a proper frame, wheels, tires and drive train.

Everything. It's a FWD cradle flipped 180* and mounted backwards. It was never designed to be in the back of a car, much less a sports car. The difference between the older suspension and the newer is night and day. My little brother used to own an 86 GT that had a lot of stuff done to the cradle including solid bushings. When I would drive his car after driving mine it felt like a minivan.

You don't have to, entirely your decision. And I'm sure at this point in time finding an 88 for part out would be very difficult. But you can spend a ton of money and time on the older suspension and it won't be as good as the newer stuff right out of the box. There's a Fiero 3 feet from me that's got a cradle swap in it. I would have been mad if I didn't know any better and had tried upgrading the original cradle first. Just sayin'.

The '88 is a slight improvement over the '84-'87. It's still a twisty chassis powered by a washing machine engine.