Jesus dude impressive work. I'm looking at doing some front end upgrades myself but nothing this intense 
Jesus dude impressive work. I'm looking at doing some front end upgrades myself but nothing this intense
Pretty good weekend overall but the car seems to be losing a significant amount of power as it gets hot. My fastest lap was the first hot lap of the entire weekend, despite not having driven the car for 6 months and having a bit of lap traffic. By the end of the weekend my friend's S2K was easily walking away. 
My fastest lap for each session was always one of the first two or three, with each subsequent lap dropping by a few seconds each. I thought the issue might be due to tire pressures.. I'm currently running the Hankook RS3s at ~37 psi hot. Perhaps they like a lower pressure and my lap times are going up because the tire pressure is rising too high. I'm going to try lower tire pressures at the next event to see if that might be the problem. However, the sidewall flex I get from these tires is not too encouraging to lower pressures... refer to pic below. I'll probably book a dyno test soon so I can see if my motor is doing OK (I think it's not). 
Hello GRMers, it has been a long time! Brief update leading up to 2022 before I get into the really really good stuff: In 2016 my clutch pressure plate failed during a track day at Buttonwillow and I limped the car to my friend's shop in Tehachapi. Then I had to move from my rental house (the owners decided to move back in), and didn't have a garage to work on the car. Having to drive 2 hours to see my car, combined with scope creep (rewiring the firewall bulkhead, and developing a new cooling system), it took awhile to get the car back together again. Then I bought a house, started a job that had me traveling 30% of the year, and well, yeah. tl;dr: life happened.
About a year ago I really started getting the drive to work on the car again. I dusted off my old CAD work for front uprights, started scanning a bunch of parts using photogrammetry, eventually bought a 3D scanner, built a 3D printer, and got into a really good workflow with a focus on durability, driveability, and big MFing tires.
I'll be spreading out the updates over the next few posts, so stay tuned. For today, we start with the first step toward getting the Fiero ready again for track duty: front wheel bearings.
The 1988 Fiero has a unique bolt-on bearing/hub cartridge that isn't used in any other vehicle. It has the lowest flange-to-flange offset of any bearing package made for a production car, and the knuckle bore is tinier than most rear bearings on FWD cars. The OEM 1988 Fiero bearings were long ago discontinued by GM, and various aftermarket replacements have been attempted, with some successful enough to survive a single weekend at the track on OK tires, but nothing better than that. Even the best suffered from occasional flange separation. Not for track use.
I've worked through a number of designs over the past 15 years to adapt larger more durable hubs to the stock knuckles, but never got anywhere I was happy with. Finally I decided it was time to build a new knuckle.
First I needed reference geometry. I scanned the stock Fiero front knuckle by taking a lot of photos and running them through RealityCapture, which generates a 3D mesh from those images. This technique can be as accurate as a 3D scanner, but it does take quite a bit more work as you have to manually add control points to relate images to each other.
Next I designed a new knuckle that retained the same hard points as the Fiero but took a new hub/bearing package and brakes. I decided to standardize on modern GM because there are so many interchangeable rotor+caliper options with the same offsets and mounting patterns. With a single knuckle I could go swap between little W-body sliding caliper brakes up to 14+" CTS-V 6-piston Brembos, and even C7 ZR1 Carbon-Ceramic brakes.
Initially I based on my design on the 3-bolt pattern hub that allows for interchange between C5/6/C7 (5x4.75), Camaro/CTS (5x120), and Chrysler 300M (5x114.3). Below are some 3d-printed prototypes with this design.
Unfortunately the 3 bolt pattern is very hard to package within the Fiero ball joint and tie rod boss locations. The swaybar endlink also wants to interfere with the bolt bosses. No matter how I clocked it, something got in the way. Then I discovered the C8 Corvette front hub, which uses a 4 bolt pattern but is otherwise the same as the 6th-gen Camaro hub, including the 5x120 bolt pattern. This meant no more 5x4.75 or 5x114.3 option, but there are PLENTY of wheels for BMWs that will work with a simple hubcentric ring. The same brake interchange would work, although rotor fitment becomes a bit restricted due to GM putting a step inside the hat that's just a few mm smaller than the 5x120 hub flanges.
Here is a size comparison between the 1988 Fiero front bearing unit and the C8:
The image below shows the C8 hub mounted to a 3D printed ABS knuckle for test fitment. I also at this point in the development moved to a modular knuckle with a bolt-on steering arm. This allows me to use the same knuckle on the left and right sides of the car, and fabricate different steering arms to adjust for bump steer, ackerman, and steering ratio.
After a few iterations of 3D-printed prototypes with tweaks including adjusting to the caliper angle and overall dimensions for clearing other parts at full lock both ways and full compression, I created a manufacturing drawing package, crossed my fingers, and pulled the trigger on CNC machined parts. To be continued...
It would take at least 6 weeks to get the CNC machined knuckles, but that wasn't all I needed. I had only purchased a single hub, rotor, and caliper for test fitment. Now I needed another of each. I also needed to fabricate bolt-on steering arms, some little heat shields I designed to bolt onto the new knuckle and protect the balljoints, and much much more: hardware, brake pads, steering rod ends, tie rod adapters, rod end spacers, ball joints, ball joint sleeves for the lower control arms, and upper control arm ball joint plates. I also needed to fabricate steel ball joint taper inserts that I determined were necessary for the LBJ to spread the load in the aluminum knuckle.
I had settled on using K6145 lower ball joints which are bigger than the stock Fiero ones and are commonly available with different stud heights and friction levels. For the uppers I'm using C4 ball joints which bolt into an off the shelf adjustable upper control arm plate from SPC, and have the right taper pitch and length to work with an aluminum upright. This will make replacement parts easy to find, and I know they'll be available for a long time.
After a few weeks of sourcing and ordering, everything started to show up. It was looking like a complete kit minus the knuckles themselves!
I picked up a lathe during the pandemic, which came in very handy for cutting these knuckle ball joint taper inserts.
These spread the load to a larger surface area of the aluminum knuckle to prevent it deforming and loosening up under high loads.
Finally, CNC-machined aluminum uprights!!! I very very very carefully inspected them, checking all the critical dimensions against my drawings, and they were perfect save for a minor cosmetic dent.
It was so satisfying to feel my design in solid metal. The 3D-printed ABS prototypes were cooler than CAD, but they didn't feel real enough. The real thing feels SUBSTANTIAL. And everything fit! In under an hour I had fully assembled an upright with all its accoutrements.
Here you can really see the difference between the stock knuckle and bearing and the new one. Yes, the weight gain is non-trivial (16 lbs per side with C8 one-piece 320x30mm rotors and C7 calipers) but 80% of that is from the brake upgrade. Two-piece rotors save 5 lbs per side, and lightweight race caliper packages for the C8 and some C7 will fit.
Finally, mounted on the car.
Upper ball joint mounted in the correct orientation in this shot unlike above 
This is the C8 front rotor with a C7 front caliper. The C8 front caliper would also fit, as I 3D scanned a C8 front knuckle to confirm the geometry.
The next upgrade would be a two-piece rotor to drop some weight, and perhaps also the Z51 package rotor which is larger and uses a similar caliper with longer mounting lugs to bolt to the same knuckle.
You might have noticed the brake line dangling in the above photos. I love little projects that I can solve with laser-cut and bent parts, because I can quickly design and make them with a service like Send Cut Send or OSH Cut.
I whipped up a design and 7 days later had parts in hand. I tried out Send Cut Send's hardware insertion service this time. That's an M6 insert pre-installed in the bracket.
After test-fitting I spray-painted it black and bolted it in. Perfect!
Next I needed to finish the other side, then do something about the rear bearings. Despite my upgrade to J-body bearings in the back they start to get play in them after a few track days. More soon...
This is some next level work!
Awesome project. Great job on all the custom work. I just looked at the recent update, I will have to sit down and read through the whole build.
That's beautiful. I really like the modular nature.
Wow. That was worth waiting for.
With the front hubs and brakes upgraded to C8 units, it was time to address the rear. I had previously bored the stock rear knuckles out to accept J-body front hubs, which are a bit larger than the stock Fiero units, and still available new. Unfortunately they weren't enough to keep up with 200-treadwear 275s and 1600 lbs of weight on the rear axle. It would also help with wheel selection if I had the same bolt pattern front and rear. I settled on Camaro5/6 5x120 hubs which use a 3x116m mounting flange with a 91.5mm bore. The mounting pattern is shared with C5/6/C7/300M/Camaro5/ATS/W-body/etc. The hubs I selected accept a large 33T spline, making them compatible with various Porsche 930 style CV axle stubs as well as some W-body outer CV joints that accept my stock Fiero shafts.
The reason I didn't use the C7 rear hub is because it has a 5x4.75 bolt pattern, 12mm studs, and a different size brake and wheel pilot than my front C8 hubs. Would rear C8 hubs have worked? Maybe, but the 4-bolt pattern would have been harder to package around the strut mount and suspension link mounting points.
The Camaro5/6 rear Brembo calipers are identical to the C7 rear Brembos save for the paint colors. Plenty of options for calipers from the GM parts bin.
I started my design by 3D scanning the 1988 Fiero rear upright, C7 rear knuckle, and Camaro5 rear knuckle. From the scans I could figure out where I needed to place the hub mounting surface to maintain the stock Fiero wheel offset. I also wanted to make the drum-in-hat parking brake functional, so I scanned the C7 backing plate separately to get a good view of both sides. The Camaro parking brake shoes are the same, but it has a different cable arrangement that looked more difficult to package than the C7 parts, so I decided to design for compatibility with the C7 backing plate and cables.
You might also notice the caliper for the Fiero and Camaro is trailing instead of leading. GM gets away with using the same calipers between the Corvette and Camaro by just flipping them left to right... and not using staggered piston sizes.
The rear upright is a much more substantial piece than the fronts. Rear axle weight on my car is 1600 lbs (vs 1250 for the front), and the size is much larger due to the tall mounting boss for the strut. Because of this, I chose to go with a fabricated steel design for the rear. Machining this from billet is possible, but it would have to start from a massive block of material, and require a lot of machining time. Steel is also a lot easier to rework if there are any fitment issues.
This image shows the new upright with the stock 1988 Fiero rear upright overlayed on the model. The major differences you can see here are the lowered strut mount, the caliper bracket moved from trailing to leading, and all of the multilink attachment points moved downward by 45mm to improve camber gain and roll center characteristics. This effectively results in it being a drop knuckle.
It's not the most efficient design in terms of weight but I wanted to get to usable part quickly as I was really eager to drive the car, and the parts are relatively cheap to iterate on compared to the billet aluminum front knuckles, which I had to get right the first time. I did run some simulations with traction, braking, and cornering loads and it's way overbuilt.
In a future iteration I'll reduce the weight of the strut mount and use a double shear clevis for the trailing link instead of that big heavy spacer at the bottom. I can also thin out a lot of the overall structure.
I was happy enough with the design so I created the cut and bend drawings, sent them off to Send Cut Send, and went on a work trip for a week.
Got home from my work trip to a pile of boxes sitting by the garage.. including one containing these parts.
Everything looked pretty good out of the box. I had to tweak a couple bend angles but it was easy enough to do with my big vise and a hammer.
I designed the assembly such that it's self aligning. Everything that defines the suspension geometry bolts together, then slots into the front plate that holds the hub and caliper.
NICE!
Since the parts locate against each other, the welding fixture is very simple -- it's just a plate that the upright bolts down to thorugh the hub, caliper, and trailing link holes. The strut mount bolts and the lateral link rod end spacers keep their respective pieces in place.
Painted and done!
... and successfully test fit onto the car.
I only needed to adapt a few parts -- I used stock 1988 Fiero front brake hoses instead of rears, and I swapped the outer CV joints out for early 2000's W-body CVs, which have the larger 33 tooth spline but have inner starts that accept the Fiero axle shafts.
The rod end lateral links are 100% off the shelf parts. I designed the pockets in the upright to have the correct width for the 5/8 to 12mm misalignment spacers I'm using, and the inboard side just needed a small shim/washer to fit in the Fiero subframe pockets.
So now I have big bad brakes and bearings on all four corners, and no wheels that fit....
Logically, if I'm going through the trouble of putting heavy duty bearings on this car with big M14 studs, I should install the fattest tires that can fit... right?
After going back and forth on various levels of aggressiveness I finally decided to just F it. Go big or go home. I ordered 315 Nankangs for the rear and -- in proportion to the car's weight distribution -- 265s for the front.
Apex Wheels has a great selection of meaty rims in Camaro and BMW fitments -- perfect for my new 5x120 hubs. I picked out satin black SM-10s in 18x9.5 ET35 for the front and 18x11 ET35 for the rear. The rears are Camaro fitment so they didn't even need hubcentric rings, while the fronts have a small ring to adapt BMW centerbore to the GM hubs.
Happy delivery day!
The next day a mobile tire installer came out and by sunset I had the car back on the ground with all the meats.
Yes, the rears are WAY too close to the fender even with my 500 lb/in springs, but I had to take some pics before I raised it up and lengthened the bump stop.
Believe it or not the fronts were fine like this, just some minor rubbing on the plastic fender liner under hard braking.
DIYing your spindles? Wow. Just wow.
I didn't realize you were in the Los Angeles area. What mobile tire shop did you use? My buddy owns zip tire and I'm trying to invest in it as he and the company are phenomenal and I was wondering if you happened to use him.
jfryjfry said:I didn't realize you were in the Los Angeles area. What mobile tire shop did you use? My buddy owns zip tire and I'm trying to invest in it as he and the company are phenomenal and I was wondering if you happened to use him.
Yep I used ZipTire. Other than being 3 hours late for the appointment they did a great job. The tech was very careful with my new wheels. I would hire them again.
The overly-observant of you may have noticed something peculiar about my knuckles -- an extra feature that doesn't belong on a Fiero.
I'm talking about the one circled here:
Yes indeed, that is a wheel speed sensor boss.
In my absence from tracking the car, I almost abandoned the Fiero platform due to the lack of ABS and its propensity to lock the front right due to horrible weight balance. Many times have I flat-spotted a brand new front right tire going into Off-Ramp when running Buttonwillow clockwise.
Then I discovered MK60 retrofits... particularly the MK60e5 variant which has more detailed CAN output, proportional valves, and built-in pressure sensors. It is no coincidence that I used hubs with magnetic encoder rings that are directly compatible with E90 BMW wheel speed sensors.
Here is the E90 front wheel speed sensor installed on my custom front upright. In hindsight, I should have mirrored the sensor boss so that the cable lengths would be correct from left to right, but I made it work.
The rear uses --- you guessed -- a rear BMW E90 wheel speed sensor.
I routed the wheel speed sensors along the brake hoses using 3d-printed Nylon clips. I had to reprint them all after a week as I had skipped the annealing step, which turns out to be critical for preventing the material from creeping even under light loads. I reprinted in Nylon and then in Nylon+CF. So far it looks like the carbon fiber fill isn't necessary. The annealing is the important part. I annealed both the plain Nylon and Nylon+Carbon Fiber parts at 80*C for 6 hours. No more creep!
With the wheel speed sensors in place, I still had another accessory to install. The DSC sensorcluster is an inertial measurement unit with gyros and accelerometers for measuring braking and cornering forces, as well as the rotation rate of the car. This feeds into the MK60e5 brain so it can decide how much pressure should be applied to each corner of the car. The MK60e5 isn't just an ABS unit but also a DSC (dynamic stability control) system. I don't have the DSC portion working yet, but the DSC sensor still feeds into some of the ABS calculations, especially for dynamic front-to-rear biasing.
I hoped to mount the sensor under the front edge of the driver seat where it is on a stock E90, but my floor plan would have me kicking it with my shoe every time I got in and out of the car. Instead I located it on the centerline of the car directly in front of the shifter.
Unlike the MK60, the MK60e5 can actually have a custom position for the sensor coded in. I'll get into my custom coding a little later. Suffice to say: this won't mess up the ABS, because I told it what I did.
Now I had wheel speed sensors, an accelerometer, and a stock Fiero booster and master cylinder with the stock prop valve... and only one brake line going to the rear of the car. Ok, lots of work left. Let's get to it.
New brake line to the rear left caliper... Done.
3D scan the stock booster area, E90 booster & master and MK60E5 ABS/DSC... Done.
Design and fabricate an adapter for the brake booster.... Done.
Design and fabricate a bracket for the MK60e5... Done.
Connect the lines... Done.
Wiring and fuses.... Done.
Using a laptop with BMW software to bleed the brakes on a Fiero is a very odd situation to be in. But also... Done.
... and finally out in the sun ready for its maiden voyage with ABS.
Now you can see the extra height I had to add to keep the new tires off the bodywork. It's a little exaggerated here with the camera angle, and doesn't look as bad in person. Really need to get around to fender flares though...
Anyway, it looks sunny, but it had actually just cleared up after a long rain. Great conditions for testing ABS! I went for a short 15 min drive, testing full panic mode braking through puddles and sandy spots on the road --- no lock up and NO DRAMA. Wow. I was logging nearly 1.0g on wet dirty roads with cold tires and un-bedded pads from Autozone. Bananas!
A few more notes about this setup:
My custom programming for the MK60e5 is as follows. I entered these using NCS Dummy then coded with NCS Expert.
This is so cool. Very well done.
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