sbelles

Or a wheel bearing going out.

the_vetman

I found this out the hard way..

ProCoach

^^THIS^^

The hub (on which the rotor is mounted) has to distend side-to-side to make the rotor push the pads back, which then pushes the pistons back into the calipers. Next time you push the pedal, you're pushing the pistons out towards the rotors, but may need more than one to get SHORT travel.

This used to be MUCH more common when the stub axles on cars were not as beefy, when tapered roller bearings were used (instead of sealed, double row, non tapered bearings so common now) and when tires were a lot skinnier.

The reason why the drivers I work with do it is reflexively. Most have had some sort of failure that led to an accident, so they check it as a matter of course.

The only time I have seen people experience this is if they hit exit curbing obliquely, instead of parallel.

TXE36

I just do it to see if the pressure is there. Don't want to find out as I'm passing the brake markers...

-Mike

Jason987.2

Late to this party...
Is there an in-car video of someone making turn 2 at Laguna after losing brakes?
TIA

DTMiller

No, that would be impossible. No one could do that.

Veloce Raptor

Lol

mark kibort

Yes, i lost my brakes .. it burst going down in to turn 2 . a downshift and a little push of the front tires, helped save the turn (and the car from going into the sand trap)

people mock what they dont understand

Well, i guess you can call me "no one" from now on

mark kibort

actually NO.. its nothing to do with rubble strips, brake zone surfaces, or even calipers. it has to do with the movement side to side of the rotor, and that is controlled by the hub. if the hub is loose or the rotor has some run out (or both) you get pad knock back. most usual cause is loose wheel bearings.

Veloce Raptor

Yes you're right. All of the above can be contributing factors to pad knock back. This is why I and pretty much every other pro I know does the tiny 1-pedal left foot tap on straightaways regardless of track. I never want to be surprised, and overcome by events...

TXE36

Doesn't have to. If I put two croquet ***** together, put my foot on one of them, and strike that one with a mallet, the other ball is pushed away via the force through the fixed ball even though it didn't move.

Something pounding on the suspension can move the brake pads in the same way.

-Mike

mark kibort

Hey Mike.... im not sure im understanding what you are saying here. I understand the concept of the cue ball, but as far as the brake pads. something has to apply a force to the pads. just a shock, vertically (as that would be the force based on a high g instance) would not put any force on the pads . unless im not understanding your point.
what im saying is that in most cases, a loose wheel bearing that allows the hub to move with a vertical angle ((changing camber slightly but pivoting on the hub) will allow the rotor to press on the pads, pushing them back on the calipers and displacing fluid... loose wheel bearings are almost always the culprit, or a rotor with high run out (warped). natural vibration of a rotor that has a little run out, can do this too at very high speeds (like a long straight) this is why you do the brake tap, about a couple of seconds before a hard braking zone approach.

bouncing around on a rubble strip or bouncy brake zone area is not going to cause pad knock back. these are generally vertical loads in the plane of the rotor... so they dont move side to side, but vertically which doesnt effect pad position relative to the caliper pistons.
yep and im totally in agreement with you there......however, there is something that cant be forecast or tested, and thats a line that bursts under pressure as i had at laguna. so yes, you can survive a blown line on a few turn approaches with proper downshift and steering technique. BUT, it is only a few turns, LIKE Laguna turn 2 where there is enough pavement to allow forces to help you out a bit! coasting will always end up causing a big problem..

Pad knockback is due to really only two factors.. the movement of hub, (directly connected to the rotor) which is connected to the rotor that moves inward or outward based on bearing looseness. or rotor runout.

sbelles

A couple of years ago at Monticello I had a RR going out. It was OK everywhere else but going through flick flack and then the high speed left after it with lots of bump and curb on both turns I would have to pump the **** out of them into the hairpin. If I wouldn't have checked them the first time it could have been ugly. I finished the race but it was touch and go a few times.

mark kibort

Ive seen it at Laguna seca at the exit of the corkscrew. the highest compression 1.5 g loading turn in racing. the high lateral gs with high positive gs, makes for a tremendous amount of stress on the hubs . if you have any slop in the bearings, watch the pedal go to the floor before turn 10.

ProCoach

Nope, Mark. I saw 1.55 g sustained at the toe of the boot today in an R7-equipped 964.

There's plenty of corners greater than T8A at Laguna Seca, although that's a good one. I measure 2.25 in a flat bottom forty year old F1 car there. And that is at speeds below the aero threshold.