Braking system concern after track incident

[SubiePig]

Regardless of why the bolt let go, my question was this:

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.

If a failure happens, that is the redundancy I was concerned with.

the master still had fluid, the line was intact and nothing was leaking. The Piston was still in the caliper, barely but it was in.

[diss7]

Originally Posted by Dave-ROR

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.

I agree with what you're saying. Fwiw I use battery guns not air.
Like you, I decide if it's a bolt that's as per your list above, of whether it's just "mounting chuck of steel a, to chunk of steel b"

I also agree that's it's done to save time. That's why I do it as well! I think after awhile you get a good feel of what your tools do. As I said above, I know my middle gun at full tti won't break a wheel stud. But that doesn't stop me going around them all with a power bar and impact socket in between sessions, or before a big road trip. It's not that I don't trust the gun, it's just I know if I've leant 110kg on the end of the bar, then it's tight. The middle gun seems to be able to get to that same force. But that one time I did my power bar check and found a wheel of just put on that I'd only hand threaded the nuts on and forgotten to use the gun, is why I have the habit of always rechecking them.

Back to OP. Sorry, I wasn't doubted your info of 20ftlbs, I was just commenting that it seemed light. Clearly it's what is recommended.

Also, for the purpose of stating a fact. Perfect world, I'd love to take everything apart and reinstall with absolute precision, correctly torque ing everything to exact spec. But to be brutally honest, I cbf.

[mla163]

Redundancy - yes it should have some in the odd event that something like this happens for whatever reason.

So there's nothing? Not two circuits? If you lose 1 of 4 brakes, then you can't stop? I guess the e-brake is kind of a redundancy. But that won't slow you down from 100mph without overheating. Just thinking out loud. I guess it surprising.

[Dave-ROR]

Originally Posted by SubiePig

Regardless of why the bolt let go, my question was this:

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.

If a failure happens, that is the redundancy I was concerned with.

the master still had fluid, the line was intact and nothing was leaking. The Piston was still in the caliper, barely but it was in.

I've only driven one car with a brake failure like that, it was a line. The car could brake. sorta.. it had a brief period of VERY LIGHT braking until the pedal was on the floor.. had to keep pumping it to have any sorta of brake force.

In theory the one circuit should be fine, but I don't have enough practical experience with such a failure (nor do I want to test it) to provide any more information.. sorry man.

[xwd]

The BRZ I'm sure is the same as all other Subarus in the brakes are tied in a cross pattern with regards to circuits, but there is only one MC... The ABS/EBD can vary the pressure being applied to the brakes, but if you sever a brake line or have an issue where you are using more fluid than usual, like the brake pad not being there and pushing the piston out, it's not going to help you. Did you try pumping the brakes?

I've lost a brake line in a WRX, which is similar in design and it = no brakes.

[SubiePig]

Makes sense, still sucks but at least myself and the car are okay and can move on.

[ftc~brz]

@swift996 had something break related happen at a track event if I remember correctly.
sounded similar but I could be wrong.

[diss7]

Originally Posted by SubiePig

Makes sense, still sucks but at least myself and the car are okay and can move on.

Definitely, could've been a MUCH worse outcome!

[stugray]

On my racecar (porsche 914), there are "plates" behind the caliper bolts that you bend after torquing the bolts. That keeps them from backing out.

My guess is that when you pressed the brake the pistons on that caliper just kept moving so pressure never built in the rest of the system.
If you had kept pumping, you should have eventually gotten pressure unless one of the pistons popped out of the bore...

You have me wondering now how my racecar brakes work after a failure.
My brother races a TR4 and he broke a line completely off the front caliper when he went "four off" and didnt know it until trying to slowdown at the end of the longest straight on the track. Almost blew the tranny downshifting to slowdown