Braking system concern after track incident
 

I did a track event at MSR Houston this weekend and Friday's test session I had a mechanical failure that caused me to have a bit of concern about our cars and the electronic braking system.

First off, don't use cheap torque wrenches... I had one of the bolts that holds the caliper to the slider bolt on the rear (torque spec is 20 ft.lbs.) say goodbye on track and caused the other to I am assuming back out. Needless to say the brake pads said goodbye as did the brakes coming off a long straight. I know that everything should be looked over extra careful on a track car, but it doesn't help if you don't use the right equipment and I learned that lesson. When I went for the brakes they did nothing, pedal straight to the floor each time I hit them. Granted this all happened quickly, luckily in a high run off area, coming in at 110 mph and I was just concerned about being unhurt at that point and am going off what I did to stop the car; scrub off speed as I went off track, downshift, hope for the best.

Since most brake systems are fitted with twin hydraulic circuits, with two master cylinders in tandem, in case one should fail.
Sometimes one circuit works the front brakes and one the rear brakes; or each circuit works both front brakes and one of the rear brakes; or one circuit works all four brakes and the other the front ones only. Why NOTHING happen when the rear said goodbye...



ADD version: lost rear brake caliper, braking system failed completely, should be redundancy in system unless electronic "assists" intervened instead pedal did nothing.

Sucks. You torque those bolts though? I just overtighten and impact the caliper bracket ones.

All I did to swap pads was undo the bottom slider bolt, rotate the caliper upward, drop in new pads and put the bolt back in. :/

You can overtorque the bolt by quite a bit.

Are you okay?

Sorry to hear about your experience.
Regarding the "there should be a redundancy for this" I disagree. While you may feel this way now, after the incident, from what I can gather, if they were installed correctly and or by a professional, there wouldn't have been a problem.

Not different to not doing your wheel nuts up tight. Or seat bolts up tight. Or subframe bolts up tight. If you're going to put in a redundancy for one thing not being installed correctly, there's a thousand others you'd need as well. It's not practical.

20ft lbs seems light. I think there is far to much focus on forums on correctly
Torque ing something down. This isn't NASA. I would guarantee that half the torque wrenches guys are using aren't accurate anyway.

How would I have tightened it? Impact gun. BZzzttt Bzzztt.

There's very few things I use a torque wrench on. I don't even own one. But on the rear occasion I need one, I go borrow a mates really good one. I have three impact guns though. A big snap that'll crack anything (it'll even crack a flywheel bolt on a 13b) i only use that on suspension bolts etc A medium sized one, that I use on typically 12-14mm bolts and wheel nuts (because at full tti it won't snap a stud, unlike the big gun) and a little drill that I use for 8-10mm bolts. I've found this system works well, I don't snap bolts, and I don't have things come loose. You'll find it's how every actual mechanic does it as well.

Which bolt backed out?
The one you removed or the other one?

My experience is you can not slide the slave cylinder up without losing the other bolt.

Did you forget to tighten that bolt?

Not sure what the spec is but I'm sure I put 40-50ft-lbs on those bolts.

Holy smokey! For the first few times I did use a torque wrench but later on just hand tightened these bolts


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I agree on the concept that many things don't really need to be torqued to spec.. however, auto mechanics do so because they get paid by book hours and if they can fit 12 book hours in an 8 hour day that's more money for them. They don't do so because it's the right thing to do.

Having said that, the list of things I torque are generally:
-Internal engine
-Bolts going into aluminum
-Wheels
-Brake rotor rings to hubs
-Axles (sorta - impact and then confirm it's at least at spec)
-Some suspension (when there are bushings involved)
-Crank pulleys

That's about it.

I also have a range of calibrated snap-on torque wrenches. All around 1% at three settings (low/mid/high) CW and 1-2% CCW. An off the shelf good torque wrench like a snap-on can be no better than a crap torque wrench.

I never tighten normal bolts with an impact gun. I've seen and had too many things go wrong (big air supply plus high end and powerful guns and you can EASILY break bolts). I snug with impacts turned down to their lowest setting and using the variable throttle but never tighten to completion. Some stuff I do impact until it's done.. axles are an example.

Guys in shops will turn down the guns and just impact shit on, but never forget that it's because it's easier and faster, nothing else. My M3 has a LCA with a helicoil for the shock mount because of a shop monkey with an impact.

Did the caliper come off the disk and was still hanging by the line?

Or did the caliper come completely off severing the brake line (brake fluid on the track)?

Yeah, I am fine. I babied the car back to grid using the handbrake, pulled the caliper apart, cleaned and rebuilt it, found some stock pads from a Continental World challenge teams garage next door, hardware store for bolts, Lok-Tight, and finished the weekend of 8-20 min sessions and set TTD track record. haha


http://farm9.staticflickr.com/8323/8...bb1f8a4d_c.jpg

Its a M8x1 bolt. Proper torque in some fastening situations is critical especially in tension and shear situations, this isn't one of them since those bolts merely need to hold the the slider to the caliper. Regardless an M8 bolt isn't going to hold much more torque than listed and I would rather get it to spec than He-Man everything and strip it or do the opposite and.. well the bolt vibrate out..

I was concerned about the redundancy of the hydraulic system. Not the bolts.

I tightened both. I remember going around the car and doing them twice because a friend was helping install the pads and I wanted to make sure.



My main thing is the hydraulic system more than the bolt issue. I can keep one thing, the bolt from happening again. But, I would like to know why the fronts gave on me too.

Caliper was sitting inside the wheel when I came in. Didn't have enough room to come out and brake line was fine. I checked it heavily before putting the car back together.

I would be surprised if that bolt backed out due to low torque. That bolt on most cars is very light. I want to say 15 ft-lbs on my miata. I've always done "good and tight" on those bolts because most torque wrenches don't read that low.

Maybe the bolt had grease on it, or maybe it was just hand tight. Dunno

Regardless. That's scary. I guess the e-brake still worked right?

Stugray asked as well, but did the brake line fail? Because if the brake line failed I can almost guarantee that's why you didn't have brakes anymore.

edit nevermind you answered right when I submitted.