Track Day Lessons - Suspension Bots and Throttle Cable

[Dave 53]

Had my 818 out at Buttonwillow CA over the weekend. Overall, a great time. Any time I can drive the car home is a win. I have 18,000 miles on the car and this was track days 34 and 35.

Buttonwillow is a 240 miles drive, so I only go there if it's a two-day event. The 240 miles is a bit stressful because it's going to be difficult to get a tow home if I needed it. But, I'm feeling I've got my car very well sorted out for track duty. I've broken and improved everything that can be broken, so I'm good to go. Right?

Three things happened at the track that I thing are worth sharing so others can learn from it.

First thing... The last session on Saturday, as soon as I got out on track, the car felt wobbly in turns. I IMMEDIATLY got off the gas, limped in and discovered the Jesus nut was missing! This is for the bolt that holds the rear two lower lateral arms to the spindle. Where to find a replacement nut? There is a shop at the track that had a bin with about 300 pounds of used nuts and bolts and I found one! Fix made. Ready for Sunday.

After watching the FFR Cobra at Willow Springs accident, my unprofessional analysis is, a nut in his suspension came loose. He says it felt loose for a second, then felt okay. Same symptoms I was feeling. Since viewing that accident, I started putting witness paint on every suspension bolt and I painstakingly inspect the witness paint on every bolt before every track day. When I'm feeling too lazy to jack the car up and look, I think of this video. After 33 track days, I've never discovered a loose nut and that Jesus nut was tight the day before. It seems crazy to think back on it now, but I will admit, I never put any Loctite on any of those nuts. The guy at the race shop shared that he always puts one drip of Loctite red on three threads. And I will be doing that now too. Pro tip #1 - check your suspension nuts, Loctite, witness paint. Witness paint alone is not enough. The second something don't feel right, come to a controlled stop.




Second thing... On the first Sunday session, I slowly and progressively started to lose power. It took a couple of laps to conclude something was wrong, go into limp mode and make it back to the pits. My first thought was an intake leak, then maybe my AWIC stopped working causing the intake air temp to progressively rise cause the ECU to progressively detune the engine. I diagnosed by reviewing Cobb AP data. I was down to 22% throttle. Turns out the throttle cable was slowly slipping in the cable barrel thingy at the throttle body linkage.

The cable was too damaged to simply make an adjustment. Pro tip #2 - At the throttle cable tension adjustment, favor a position so that you can effectively make the cable longer. That way, it the barrel slips, you can adjust the cable longer to set the barrel on a fresh piece of cable. Now, I'm feeling pretty proud of myself, because I carry a spare FFR sourced cable to the track! When I pulled the old cable out, I made a discovery that I didn't expect. The cable was severely frayed where it comes out of the cable housing because it was chaffing due to the cable bracket on the intake manifold not being perfectly aligned. Looking at it, maybe the barrel didn't slip and the wire chaffed and slowly unraveled itself which stretched the wire length. Pro tip #3 - Inspect your cable and determine if it's chaffing on the cable housing as it exits the housing. Mine was and I will bend the cable mount to minimize the chaffing. Probably a good idea to inspect the peddle end too. I did put in a lot of effort to align the cable bracket at the peddle end with the wire when I built the car, but didn't think to put that same effort into the engine end.

Throttle Cable Fraying Inside.jpg

Feeling glad I didn't have a total cable failure and that I had a spare cable, I proceeded to swap in a new cable. I need to pull the dash out, but I think I have time to pull off the repair before the second session starts. Then I discovered... the new cable was too short! My next email after posting this will be to Factory Five! Question - does anyone have a source for these cables other than FFR? And how long does it need to be?!?! I don't want to tear it all back apart just to measure.

Throttle Cable Too Short.jpg

When I tossed the spare cable into my track bag, I noticed that it included extra barrel of various sizes. I remember thinking about taking the odd sized barrels out, but then thought, they take up no space, so I left them. And it's a good thing! I spliced two wires together with the extra large barrel. I missed the second session, but made the rest and drove home. Pro tip #4 - Have a spare cable on hand (in your garage) and measure it!

Throttole Cable Fix.jpg

Third thing... There are a few track day etiquette items and a big one is, don't run out of gas! Some events fine you if you need a tow off due to running out of gas. On the fourth Sunday session (after the throttle cable drama), as I rounded the last corner and I see the checkered flag halfway down the straight, the engine started sputtering and I immediately knew I was out of gas! I was able to coast to a track exit, but I did need a very short tow off. When the tow driver asked me what I thought happened, I told him maybe a throttle cable issue. Thankfully, no delay to the next run group. Pro tip # 5 - don't go out on track with any less than half a tank!

Met another 818 owner / Lemons racer. He was there with his Exomotive Exocet and Lemons car. Paul from So. Cal. Says he's not on our forum.

Side note: A bunch of Tesla's had their own run group. They go 15 minutes instead of 20. The first known Cyber Truck to turn track laps...

Cyber Truck.jpg

I drove home - it was a successful weekend.

[Bicyclops]

About bolts loosening - my car had started pulling left under acceleration and darting right when I would lift for a shift. I've got nearly 3Kmiles on her. It was getting scary so I did another string alignment on it and it got a lot worse. I took it to an alignment shop and they got it straight but discovered that with it up in the air, you could shake the left rear wheel substantially. Pretty scary stuff. I got it home and found a lot of loose bolts. The jesus bolt through the lateral arms was the worst of them. I know I had all of them tight. I used AN bolts and nylocks in place of the FFR supplied grade 5 hardware and even some of those loosened. Never seen that before. I used aftermarket transverse arms with rod end bearings instead of the rubber bushings so maybe the shock loads and vibration got to them. I'm going to start checking all the suspension bolts every thousand miles until I start to trust it more. It'd be nice to be able to do them on oil changes. I do drive it hard on canyon roads. Lots of side loads.

Ed