Real Racecar Stuff - Billet Knuckles!

There’s a weak point in the SW20 chassis.

“It’s the snap oversteer geometry!” Well yeah, but not that.

“It’s the turbo engine designed in the 1980s!” Well yeah, not that.

“It’s the antiquated parts bin Macpherson suspension!” Well yeah, but not that.

Not very many people have found this weakness, but it exists, it’s the dinky front knuckle and hub design. If you pull the front knuckle off a SW20, it’s surprising how small it looks. The guys endurance racing these cars seemed to have found the weakness first. Bearing and hub failures are inevitable. The bearings can still be found easily, but the hubs are quickly becoming unobtanium. The heat and torque on the hubs as a result of long racing periods or very sticky tires seems to crack them. When they fail, it can be catastrophic…or you can limp the car back into the pits (the brake caliper “holds” the wheel on usually).

Troy Truleo had this problem A LOT with his champcar racing. So, he designed and built some billet aluminum front knuckles designed to be used with a MUCH beefier 370z bearing/hub unit. The big bonus is these hubs just bolt right in, no press needed. The 370z units can be found for about $100/pair too, very reasonable. He had to make a minimum run of these for machining and sold the other sets. I was lucky enough to pick up one of the last pair.

I bought these knuckles last winter and tried installing them in the middle of the season… but couldn’t figure out a solution for the ABS, so I went back to OEM for the last few track days. My very last track day I had some bad braking shuddering only getting worse. Upon inspection, it appears my rotor had been hitting the caliper, meaning likely the hub was failing. I still can’t find any cracks, but they generally stress fracture where it can’t be seen, behind the bearing.

Troy designed the kits to work with the Wilhelm BBK, and other brakes. So he sent me the wilwood caliper adaptors, and rotor top hats with a larger center bore.

First, we need to change the wheel studs on the 370z hubs, Nissan uses a different thread pitch. I just used my old OEM ones. Those bearing style wheel stud install tools are a VERY worthy tool investment for $30.

As mentioned before, the OEM MR2 hub is 60mm, and the 370z is 66mm, meaning we needed different rotor top hats.

Front rotors put together. These fronts have held up really well to a season of abuse with the ST43 pads.

Truleo also designed the billet knuckles to have some of the geometry correction needed for the SW20 chassis. But, the Wilhelm front RCAs would need to be milled down to .80” to match the additional geometry Alex had designed for his kit. They’re 1.5” if I recall from him. This was measured from center of the hub/bearing.

Another thing I’m noticing when writing this up is the steering arm is lower on the Truleo knuckles. Meaning you should likely shorten the Wilhelm steering drop post to match as well. This is something I will have to sort out this winter. The distance between center of hub to strut mount holes are the same, and that’s easily adjustable with coilovers.

I used the 370z torque spec for the bearing/hub unit. I believe it was 60 ft-lbs.

First test fit, things seemed to play together nicely.

Another item needing some addressing was the brake caliper mount. The Truleo caliper mounts are not threaded, so you have to through bolt the caliper to the knucke. I used some high grade bolts, special locking nuts, split lock washers, and blue loc-tite. I would not trust the loctite alone with the heat the braking system sees.

Next we needed to mill down the RCAs. Since I do not own a mill I got creative here. I cut the RCAs as squarely as I could with a band saw, then flattened them with a flappy disc on a grinder. The ball joints have a male style fitting needed to transfer the forces correctly to the lower control arm. Otherwise the ball joint will not seat correctly and you could shear the ball joint bolts probably catastrophically. The size is just a hair bigger than 1-3/8”. So I got a 1-3/8” Forstner style bit to try with my drill press. Since the RCAs are aluminum I turned my drill to the slowest setting and used care and cutting oil to chip away until it was deep enough.

Light pressure here, let the tool do the work. Once it was deep enough I busted out a small flappy disc on a rotary tool (big dremel) to open up the hole a few mm. It was still pretty dang round and the ball joint engagement felt solid. It likely wasn’t perfectly flat cut surface…but it mounts to a ball joint so I figured I have a window of fudge factor as long as the ball joint isn’t binding.

Here it is mounted with correct length bolts.

All mounted up, double check those torque specs please!

This leads us to the last system I needed to get working with this mod, the ABS. You can tell me you’re faster without ABS, but I know for a fact ABS makes me about 2 seconds faster at my local track, so I prefer to keep it. I found this out at this years GTA when I had ABS removed to save weight…only to go slower.

Truleo said he was able to use BMW e46 abs sensors with the 370z hubs. The 370z hubs have a magnetic tone ring behind a rubber seal near the bearing. So, I gave those a shot. They seemed to mount correctly, and I had no ABS codes… but no ABS? Seems there’s more to it than I hoped.

I figured… they are 370z hubs, why not try 370z sensors? They should read the tone ring they were designed for?

Got them installed within factory spec between the sensor and tone ring. I accidentally had one wired backwards, and did get an ABS error code, so we knew that was working. Repaired the wiring, and went for a test drive, annnnnd just lock up… no ABS. Alex came to the rescue with a solid theory. Some newer ABS systems have the magnet in the tone ring and hall effect sensor is reading that. Some ABS systems (like MR2) have the magnet in the sensor and the tone ring is regular steel teeth to cause a pulse signal. It seems we were trying to use a different sensor style that the MR2 ABS ecu could see there was a sensor…but no signal if the wheel had locked up.

Basically, I either needed to re-work the entire ABS system, or try and make the MR2 sensors work.

I decided to attempt making the MR2 system work. The MR2 sensor is magnetic, and the 370x tone ring is magnetic, so it’s very likely the sensor would not read the 370z tone ring correctly, or at all. I needed to add a MR2 tone ring to the 370z hub.

You can get MR2 tone rings for about $20 each still, so I picked up a pair, and some steel flat bar to use as a spoke.

With a little bit of careful TIG welding, I had OEM tone rings on the 370z hubs! You can see the OEM 370z tone ring in the pic below (it’s behind the brown rubber seal).

With the bearing/hub installed it fit really nicely! I built some temporary brackets to hold the MR2 sensors in place correctly and put the car back together for a test drive.

The first stop I knew it was working, we had ABS! I gave the car a quick and dirty alignment and went for a longer test drive. ABS is working great, but really sensitive. It might be due to the cold temperatures here now, and 200tw tires not happy.

We’ll see with more testing later!

Since I’ve started this project, Alex has announced he’s coming out with his own front knuckles utilizing a Toyota hub/bearing unit! They look really nice. If I have any issues with these I will likely be giving him a call about ordering a pair (or all four, why not, he makes some rear knuckles as well now).

As an added bonus, these did save 2 pounds per wheel, unsprung!

Stay tuned, we have another blog post coming soon, about aerodynamics and more weight savings!