84-87 Front Suspension for Endurance Racing

[neophile_17]

Hello Guys,

My team races in the 24 Hours of LeMons and we've been battling for a B Class win for, well a long time. I took one race off and the guys got it done without me. I am sorry I missed the big win, but now it's time for upgrades to compete in A Class. I had a couple schemes on the back burner that just seemed too much for a B Class car. One is to revamp the front suspension. This thread is intended to be a brain dump / sanity check for that project. Here are three areas that I am looking to improve compared to our current setup which is modified 84-87 parts with 11.7" brakes.

1) Reliability/ Durability - The stock wheel bearings last about 24hours on track (1 weekend) & breaking a ball joint is terrifying
2) Adjustability - Rewelding the upper bearing shells got us better caster and camber but it's not adjustable or enough
3) More Rubber - 7" Wide wheels are good but 8" is better and we can go wider out back while staying balanced

Now that the groundwork is laid, here is the plan. From the wheels in...

- 4th gen F-Body wheels, 17" by 8" with a 4-3/4" bolt circle. Considering 5" bolt circle stuff as an alternate.
- ~12" Rotor - either 3rd gen F-body 1LE or 4th gen vette. 'Metric' calipers.
- Jegs Circle track "Metric" knuckle with "Pinto" Steering Arm. This knuckle is taller and beefier but has a similar kingpin angle. The taller knuckle also improves dynamic camber. If they're tough enough for circle track shenanigans they are overkill for us and I'm good with that.
- 4th gen vette outer tie rod ends.
- Hybrid Chrysler/4th gen vette circle track lower ball joints. These will need inserts welded into the lower control arms. I may buy the WCF tubular lower control arms and modify them, or ask WCF to weld the Chrysler sleeve in instead.
- 78-88 G-Body Upper Ball Joint. The WCF upper adjustable control arms look like the ticket but with a different ball joint plate. Any one know why the WCF ball joint plate is so narrow? I'm hoping this was done to clear smaller wheels or save material / weight.

Most of these parts I already have with the exception of the upper and lower control arms. Any thoughts or advice before I contact WCF to get those started?

Thanks for reading!

Sam

[ericjon262]

I have C5 vette calipers on the front(4th gen F body are very similar), and honestly, I think they're a bit much, they're heavy and take up a ton of space, I'm actually looking for different calipers to install when I design my own knuckles, but that's still a ways off.

Will is developing knuckles that use C5 (6?)(7?) wheel bearings, which should overcome any strength issues, and be relatively easy to get.

can you remind us of everything done to the car up until now?

[The Dark Side of Will]

For the rear, are you still running Fiero knuckles or have you upgraded? The biggest bolt-in knuckle GM ever made is from the '92(?) to '96 Dustbuster minivan.
Get the axles, knuckles, hubs, brakes & ball joints from the minivan. The outer CVs have 33 splines where they plug into the hub. The outer CVs *should* plug right onto Fiero manual transmission axles, but I have not verified that yet. The minivan brakes are the same as the LT1 F-Body front brakes. These have the same piston diameter as Metric front calipers, so they're a good combo for Fieros. The ball joint bolts into the Fiero control arm, but has a larger shank where the knuckle pinches it.

If you drill the threads out of the hub mounting holes in the Dustbuster knuckles and spot-face the inboard side of the knuckle, you can bolt up Corvette wheel bearings. C6 Z06 and all C7s use the same 33 spline outer CV to hub interface. I have verified this.

Are you using 3rd Gen F-body front calipers? Try 4WD S10 front calipers instead... The 4WD S10 calipers can be used with stock Fiero brake lines.

I'm interested to hear about how you broke a ball joint. My upgrade plans involved keeping the stock ball joints, but maybe that's not a great plan.

[neophile_17]

can you remind us of everything done to the car up until now?

Currently we have an oddball one-off brake setup on the front. I took the 11.25" Lebaron upgrade bracket and stretched it to work with an 11.7" x .8" subaru rotor. I used the Wilwood iron D154 caliper with a 2" piston instead of the stock 'metric' stuff for quality, diamater, and weight. The 'hubs' are cut down Fiero rotors with Z26 wheels. This setup is heavier than Fiero stuff but it's appropriate for what we need. Out back are 12" x .8" 4th gen vette rotors and the same Wilwood caliper with vette "sawblade" wheels. No complaints in the brakes department. The only reason I'm changing the front brake setup is to match the new wheel bolt pattern and because the bracket will have to change for the new knuckle. I expect the same performance or a sleight improvement.

We have a version of Will's anti-dive modification. This was a big improvement.

We have 4th gen F-Body front springs cut to an appropriate length up front. The spring rate is ~ 425lb/in.

We took the upper control arms, removed the bushing shells, die ground the holes for more caster/camber, and then welded the shells back in. This is crude but it works pretty well. We gained about 2 degrees of caster and 1.5 degrees of camber.

For the rear, are you still running Fiero knuckles or have you upgraded? The biggest bolt-in knuckle GM ever made is from the '92(?) to '96 Dustbuster minivan.
Get the axles, knuckles, hubs, brakes & ball joints from the minivan. The outer CVs have 33 splines where they plug into the hub. The outer CVs *should* plug right onto Fiero manual transmission axles, but I have not verified that yet. The minivan brakes are the same as the LT1 F-Body front brakes. These have the same piston diameter as Metric front calipers, so they're a good combo for Fieros. The ball joint bolts into the Fiero control arm, but has a larger shank where the knuckle pinches it.

If you drill the threads out of the hub mounting holes in the Dustbuster knuckles and spot-face the inboard side of the knuckle, you can bolt up Corvette wheel bearings. C6 Z06 and all C7s use the same 33 spline outer CV to hub interface. I have verified this.

Are you using 3rd Gen F-body front calipers? Try 4WD S10 front calipers instead... The 4WD S10 calipers can be used with stock Fiero brake lines.

I'm interested to hear about how you broke a ball joint. My upgrade plans involved keeping the stock ball joints, but maybe that's not a great plan.

Out back we are using the 90s Abody HD knuckles machined for the 4th gen vette/S10 bearing. I will probably get a set of the dustbuster knuckles and do the machine work so they're ready. Knock on wood, our current setup has given us no issue over the past 5 years. I didn't use an axle spacer when I did this- is this only needed for the C6-Z06/C7 bearing?

Attached is a picture of the broken ball joint. Post disaster inspection hints at a couple possible cuplrits including: improper taper, contamination due to grit or corrosion, or impact damage. I really can't rule out any of them. At the end of the day all the original ball joints could be corroded and I'm not sure I trust any of the available Fiero replacements. The vette balljoint is significantly larger and I can purchase it from a manufacturer that specializess in racing suspensions. We survived one excrement extruding experience and I don't want to repeat it.

[The Dark Side of Will]

We have a version of Will's anti-dive modification. This was a big improvement.

Thanks for mentioning that! It's great to get validation from someone who's using it to the fullest!

Attached is a picture of the broken ball joint. Post disaster inspection hints at a couple possible cuplrits including: improper taper, contamination due to grit or corrosion, or impact damage. I really can't rule out any of them. At the end of the day all the original ball joints could be corroded and I'm not sure I trust any of the available Fiero replacements. The vette balljoint is significantly larger and I can purchase it from a manufacturer that specializess in racing suspensions. We survived one excrement extruding experience and I don't want to repeat it.

Interesting photo... easy to see where the crack nucleated and propagated through more than half the thickness of the shank before it suffered brittle fracture.

[neophile_17]

- ~12" Rotor - either 3rd gen F-body 1LE or 4th gen vette. 'Metric' calipers.

Got the 3rd gen F-body 1LE rotor last night and it will not fit due to offset. The 4th gen vette rotor is how I'll proceed.

[pmbrunelle]

Do you have a rear sway bar acting on the rear A-arm?

If the sway bar endlink acts on the strut taco instead, that makes the ball joint work less hard.

[neophile_17]

Do you have a rear sway bar acting on the rear A-arm?

If the sway bar endlink acts on the strut taco instead, that makes the ball joint work less hard.

Sway bar operates on the control arm. We have an unusually soft sway bar and spring setup in the back. Rear springs are [Edit! Not 200lb/in. actually 275lb/in. CRS set in] and the swaybar is a soda straw sized 10mm from a 2000ish CRV. We started with the stock Fiero 220lb/in. springs and a 22mm Fiero front bar in the back. The team voted to remove the rear bar entirely and I reluctantly agreed that the car was much better in emergency situations (it's LeMons) without it. I found the 10mm bar and we've all been happy since. I (finally) updated the thread where I modified the rear subframe for control arm positions so that's another factor in our rear setup.

Thanks for going on this journey with me!

Sam

[The Dark Side of Will]

That's pretty soft... what tire combo are you running? Typically the rear ends up stiffer to take advantage of the greater grip available from wider tires.
I thought the stock springs were in the 150-170# range, but I might be remembering that wrong.

[neophile_17]

That's pretty soft... what tire combo are you running? Typically the rear ends up stiffer to take advantage of the greater grip available from wider tires.
I thought the stock springs were in the 150-170# range, but I might be remembering that wrong.

I thought the WS6 package was 220lb/in. out back but I can't find the chart so I could be wrong there.

We had a combination of factors that made the car behave badly under emergency braking that prompted the [Edit! Not 200lb/in. actually 275lb/in. CRS set in] springs. But now we're happy with the balance.

Current Tires - Front 225, Rear 255
Proposed Tires - Front 245, Rear 275

[neophile_17]

Hello guys,

It works! And it came out pretty close to the original plan with just a few tweaks. One quick correction before we get into it. I thought we had 200lb/in springs out back but they were 275lb/in. Here's what we actually ended up with:

- C5 vette front wheels (17" by 8.5") / 4th gen F-Body wheels as spares (16" by 8") 4-3/4" bolt circle.
- 3/4" spacer
- 12" Rotor - 4th gen vette. 'Metric' calipers.
- Speedway (Not Jegs) Circle track "Metric" knuckle with "Pinto" Steering Arm.
- Bump steer sleeve for 5th gen camaro to connect steering rack to rod-end, replaces tie rod.
- Hybrid Chrysler/4th gen vette circle track lower ball joints. I sent sleeves to WCF and they welded them in to their tubular lower control arms instead of the Fiero sleeve.
- Chrysler screw-in Upper Ball Joint K772. WCF upper adjustable control arms but with the SPC plate for a Chrysler balljoint. The WCF ball joint plate is narrower to fit normal Fiero wheels. The K772 sleeve did clear the f-body 16" wheels once I replaced a hex head screw with a button head (7/16" diameter).

neo17_Front_Suspension.jpg (3.61 MiB) Viewed 1848 times

So it all goes together and we raced on it but how did it do? Well there's good and bad... We broke the lower control arm on one side. Fortunately, the guy driving felt something was off and came in before it tore completely. A thorough inspection revealed the crack. After it was out, he was able to break the tube in half with almost no effort. Not what I'd expect of 1.25" chromoly tube. We welded it back up with some extra support (both sides) and ran the next day with no issues. The steering angle was reduced a noticeable amount. This was annoying in the pits but not an issue on track. Using a thicker 1.25" spacer and shortening the arms will improve the turning radius and geometry slightly. I'll have to shorten the sleeves/threads on the rear of the adjustable uppers to accomplish this.

Overall I think it was a win as we have a solid and adjustable platform to work. The annoyances will be worked out next year. So what was up with the broken control arm? My analysis points to the tubing being undersized. When I ran the numbers again with the extra supports we welded in it shows that we will be OK. It would be cleaner if we hadn't done it in the field, but I think the strength is there now.

Sam

[Series8217]

That's a neat way to use some off the shelf racing parts.

Is that pic before or after the reinforcements? There is a bending load on the LCA due to the spring. The part of your LCA that carries that load looks a little wimpy.

Why the pin style mount for your front shock? Seems like you would have plenty of room for a clevis so you could run an eye mount there and not bend the poor shock shaft so much

[Shaun41178(2)]

Nice man. That's some out of the box thinking and engineering.

[neophile_17]

Thanks for the replies!

Is that pic before or after the reinforcements?

The picture is before the reinforcements. Unfortunately I don't have an after picture, car is in winter storage now. Forgive the crude paint sketch. The original tube is gray, spring plate in lighter grey, and the reinforcement is orange.

Tube_Reinforcement.png (7.47 KiB) Viewed 1825 times

The part of your LCA that carries that load looks a little wimpy.

We definitely found this out! The perspective makes it look smaller than the side tube but they are the same size. Without the reinforcements it would have to be much larger to withstand the load. I did send my notes back to WCF.

Why the pin style mount for your front shock? Seems like you would have plenty of room for a clevis so you could run an eye mount there and not bend the poor shock shaft so much

The shocks are for a G-Body. Since they are used by both the circle tack crowd and the hotrod crowd, volume allows them to be good and cheap. I miscalculated the length by about an inch (ball joint difference). I could have put a rod-end on the pin and they would have fit well with the original mounts. Unfortunately I was out of time and had to make it work with what I had.

[The Dark Side of Will]

The shocks are for a G-Body. Since they are used by both the circle tack crowd and the hotrod crowd, volume allows them to be good and cheap. I miscalculated the length by about an inch (ball joint difference). I could have put a rod-end on the pin and they would have fit well with the original mounts. Unfortunately I was out of time and had to make it work with what I had.

So they're... shorter?... than the stock Fiero shocks?
Do they have enough travel for a street car, or only enough travel for a stiffly sprung race car?

You mean you could have used a female rod-end on the lower end of the shock and connected it directly to the original mounting location? Interdasting.

[neophile_17]

So they're... shorter?... than the stock Fiero shocks?
Do they have enough travel for a street car, or only enough travel for a stiffly sprung race car?

I bought Bilstein AK1051s which I think are designed to accommodate a lowered G-Body. Between that and the knuckle height changes I ended up with more space than I expected. Running a stock knuckle and lower control arm you might be able to make it work but the assembly (with shortened rod-end) might be a little long. Our front springs are ~425lbs/in which is probably a little stiff for a daily, but about right for a weekend sportscar.

You mean you could have used a female rod-end on the lower end of the shock and connected it directly to the original mounting location? Interdasting.

Yes, this is what I did when I tried to use C4 shocks. They ended up a little too long even after I cut the rod-end short and welded it to the pin. However, the C4 shock is longer than the G-Body shock.