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June Sprints 2019

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#41
Preston Pardus

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Easily one of my favorite events all year round, and one I've been looking forward too! It's always a fun time hanging out around town and a fun track that I finally feel like I'm use too now after struggling last year.

 

Race one was pretty intense to say the least.. It was a classic Road America draft race. I made a pretty big, self-inflicted mistake on my end with 2 laps left entering turn 6, while I was riding behind Jim. Tyler pounced on my mistake, and together, we reeled Jim back down. As documented, the kink was pretty eye opening on the last lap. Tyler did an incredible job keeping the car out of the wall.

 

Race two was pretty sketch the first 1/2 of the race! I'm sure everyone else also had their interesting moments while the track was wet on racing slicks because it was an absolute handful. Danny put on, nothing short of a CLINIC in the wet conditions.

 

Big congrats to Tyler on picking up the win, it was really cool to see him win it for Dave! 

 

Here is race one's footage.. I'll edit the post tomorrow morning when I hope to have the feature race uploaded!


 

 


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#42
powerss

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Steve

Always sheered. It's really not related to braking at all. It the vertical loads and oscillation of the chatter bumps. The only other failure I had was at Indy and that is not a tough threshold braking track.

I think a shoulder on the pin would help tremendously. Mine are always broken at the stress riser between the threads and the pin surface.
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#43
tylerbrown

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I check my caliper pins after every single session to see if they have loosened.

 

When I get them new or "redone" from ESR, I loctite the pins, and torque them in with my little allen wrench, so it can't be extremely overtightened... I have had one loosen up by itself, but I just immediately replaced the whole caliper bracket and put a new pin on, thinking the loose pin might have stretched or disformed the threaded hole it threads in, but I have seen three pin shearing failures on ones that were tight when they went out on track. Only ever at Road America, all three sheared in pretty much the same spot, just inside of the threaded hole.

 

One almost caused a big wreck, the other two somehow we finished the sessions with the caliper half on the rear rotors and scraping against the wheel.


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Tyler Brown

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#44
Jim Drago

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 So do they come a bit loose over rumbles, making them more susceptible to sheer loads under braking? I think that’s more likely. I think there are other tracks with threshold braking zones from high speeds but don’t have a reputation for causing this problem so I’m less inclined to think it is from very hard braking alone.

this ^^^^


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#45
lillyweld

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Easily one of my favorite events all year round, and one I've been looking forward too! It's always a fun time hanging out around town and a fun track that I finally feel like I'm use too now after struggling last year.

 

Race one was pretty intense to say the least.. It was a classic Road America draft race. I made a pretty big, self-inflicted mistake on my end with 2 laps left entering turn 6, while I was riding behind Jim. Tyler pounced on my mistake, and together, we reeled Jim back down. As documented, the kink was pretty eye opening on the last lap. Tyler did an incredible job keeping the car out of the wall.

 

Race two was pretty sketch the first 1/2 of the race! I'm sure everyone else also had their interesting moments while the track was wet on racing slicks because it was an absolute handful. Danny put on, nothing short of a CLINIC in the wet conditions.

 

Big congrats to Tyler on picking up the win, it was really cool to see him win it for Dave! 

 

Here is race one's footage.. I'll edit the post tomorrow morning when I hope to have the feature race uploaded!


 

Thanks to everyone for sharing their videos. This is some of the best racing to watch, without exception. Really great stuff from everyone! The videos are also also great for us nubes who are still learning the ropes.


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#46
Preston Pardus

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Race two..


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#47
Steve Scheifler

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Back to sheared caliper pins, how literally should I take that? Let’s assume it is accurate. The only motion that could produce a shear load focused there is when the floating half of the caliper pivots on the upper pin as if being opened (or closed), as when changing pads. There should be very little slop/play in that normally so it’s really just the weight of the floating half of the caliper leaning against the pins as it’s “thrown forward and down” with each impact over rumbles. Much of that force is vertical through both pins. It seems like the forward component would also be through both pins, the top one being much larger of course. That doesn't seem to leave much force to shear the lower pin, and yet if they are in fact failing from shear load that seems the only answer. If the bottom pin comes even slightly loose then perhaps the caliper pivots a bit on the top pin and the bottom one takes more of the load and slaps back & forth enough to cause the failure. Can anyone come up with another answer? It probably doesn’t matter if a stronger pin is used, but I’d still like to understand it.
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#48
powerss

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Steve,  It is the upper pin that I am shearing.

Back to sheared caliper pins, how literally should I take that? Let’s assume it is accurate. The only motion that could produce a shear load focused there is when the floating half of the caliper pivots on the upper pin as if being opened (or closed), as when changing pads. There should be very little slop/play in that normally so it’s really just the weight of the floating half of the caliper leaning against the pins as it’s “thrown forward and down” with each impact over rumbles. Much of that force is vertical through both pins. It seems like the forward component would also be through both pins, the top one being much larger of course. That doesn't seem to leave much force to shear the lower pin, and yet if they are in fact failing from shear load that seems the only answer. If the bottom pin comes even slightly loose then perhaps the caliper pivots a bit on the top pin and the bottom one takes more of the load and slaps back & forth enough to cause the failure. Can anyone come up with another answer? It probably doesn’t matter if a stronger pin is used, but I’d still like to understand it.


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#49
Steve Scheifler

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Steve, It is the upper pin that I am shearing.

What??? I assume that’s true for others? On the 1.6 it’s the lower one that most often backs out, and it’s smaller so I assumed that’s the one failing. Help me out here, I no longer have an NB around and sadly got to race mine only once almost two years ago now. Is the rear caliper significantly different from the 1.6? Large diameter pin up top that you normally don’t remove, and the smaller one at the bottom that you remove to swing the piston side up for replacing pads. We have never broken either and have never seen an upper one come loose in numerous trips to Road America.

Hmmm..., this makes even less sense. I’m missing something. Help, anyone?
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#50
callumhay

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Great videos from Tyler and Preston. Thanks for sharing those. Definitely a lot to learn by watching how to maintain speed in the corners with these cars.

As far as the upper pins on the rear brakes go, I think the NB has a bigger pin than the NA. For sure I experienced the loosening with my NA. With my NB, I keep a 3/8 socket with the Allen key attachment (6mm) to add just a little extra torque compared to using the Allen alone. There is no torque spec in the shop manual for the upper pin. The lower is 25-29 foot pounds.

Cal

#51
Bench Racer

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Has anyone checked the quality of the internal and external threads? On unites which have loosened, sheared units and unites which have not failed.


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#52
Jim Drago

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Has anyone checked the quality of the internal and external threads? On unites which have loosened, sheared units and unites which have not failed.

I have a car in trailer that has this broken. When we unload, I will pull and get some pictures


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#53
Steve Scheifler

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Apparently I was mistaken about several things. It seems that the upper pin is longer and *may* be slightly larger in diameter but has the same diameter threaded section. Like I said, never had one out. And given the torque specs noted above that would be 8mm not 6mm, which makes a lot more sense anyway. My mind’s eye sees the 10mm wrench size for the lower one and the drop in diameter at the threads and comes up with the wrong answer.

Other than that the question of loads and mechanics of failure remain so I’m interested to see closeups. I think we used to have a metallurgist hanging around here.
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