Total braking system failure?

[Daniel in SD]

So, who's going to go out and unplug the the iBooster and see how much pedal force it takes to stop the car? I'm curious!
Older non-powered brake systems were nearly all drum brakes which require less force than disc brakes.

 

[MountainRatMat]

That is the parking brake building pressure in the system which forces the pedal out and to be very hard.

I'm not so sure about this in a Tesla. The parking brake is a separate device that has a motor to drive it closed, you can hear it every time you put the car in/out of park. There are actuators in the brake pedal to facilitate Autopilot and FSD.

 

[beachsideev]

My car is in the shop otherwise I'd be all over that. Sorry!

 

[Wennfred]

Take a good look at the Master cylinder as it goes up when pressing on the brakes.

Twitter

 

[MountainRatMat]

Take a good look at the Master cylinder as it goes up when pressing on the brakes.

Twitter

Do all Model 3's do this? That is crazy, I might need to look at mine.

 

[iwannam3]

Old drum brakes are "self energizing". The rotation of the brake drum pulls the shoes in harder. Bisk drakes do not self energize and require much more force, That's why they all are boosted.

 

[mongo]

Take a good look at the Master cylinder as it goes up when pressing on the brakes.

Twitter

Interesting! Disagree with the Tweet though, displacement does not mean less force, just less force for a given distance.

 

[AltLogic]

Old drum brakes are "self energizing". The rotation of the brake drum ...

forces the shoes outward against the drum. If I remember correctly. Also, I think that only works in a forward direction. At least that is what it felt like in the drum brakes I drove.

 

[Wennfred]

Waiting for MPP to come out with a discount code, maybe for Xmas and then I will get the brace.

Fred

 

[Timbo2]

I believe Audi uses the same iBooster.

From memory watching this a while ago Jason explains how the booster works in the event of failure towards the end of the video.

 

[Daniel in SD]

I believe Audi uses the same iBooster.

From memory watching this a while ago Jason explains how the booster works in the event of failure towards the end of the video.

Not so sure about that. The Audi system is brake-by-wire because they want to blend friction and regenerative braking. Tesla doesn't need to do that so the brake booster is electrically assisted and analogous to a conventional vacuum assisted system.
Could be wrong but it really wouldn't make sense to add that complexity unless you want to blend regen and friction brakes.

 

[Raro]

Yeah, that’s not a thing.

Yes it is a thing, a modern ABS module has the ability to isolate the mechanical pressure created by your foot from the individual circuits leading to the brake calipers, and to bleed pressure from said circuits, its not out of the realm of possibility that some bizarre 12V issue made the ABS module either fail or think it needed to isolate the pedal from the brake circuits.

And to echo what others have said there is a huge difference in pedal force needed on a car designed without power assisted brakes vs one that has failed power assisted brakes. stopping distance will be much greater in the later case.

Typically the pedal force would be about 2.5x greater for a given pressure target with a vacuum assisted system that is failed, so stiff but not "locked".

The Model 3 has a bosch ibooster for a brake booster, looking at how its designed it seems like it "could" completely lock up if it has no power (worm gears can not be back driven) but i dont see how bosch would design it that way in a million years, so lets assume that it has a fail safe. This would make me assume the issue in this case is with the ABS module either mechanically failing or getting the wrong commands because of the underlying 12V issue.

 

[Timbo2]

Not so sure about that. The Audi system is brake-by-wire because they want to blend friction and regenerative braking. Tesla doesn't need to do that so the brake booster is electrically assisted and analogous to a conventional vacuum assisted system.
Could be wrong but it really wouldn't make sense to add that complexity unless you want to blend regen and friction brakes.

My understanding is the OEM can either choose to blend or not blend with iBooster. Tesla chose not to and Audi wanted to mimic a conventional brake pedal and chose to do so. However, the underlying mechanics and electronics are the same.

 

[DrSmile]

I've had master cyclinders lock up on me on old cars, but the more typical issue is leakage. Based on the OP's account I think it is likely that the master did fail somehow. I'm sure it's the first thing they'll replace.

 

[Daniel in SD]

My understanding is the OEM can either choose to blend or not blend with iBooster. Tesla chose not to and Audi wanted to mimic a conventional brake pedal and chose to do so. However, the underlying mechanics and electronics are the same.

Blended regen requires an additional module that goes inline with the brake lines.
ESP® hev

The Model 3 has a bosch ibooster for a brake booster, looking at how its designed it seems like it "could" completely lock up if it has no power (worm gears can not be back driven) but i dont see how bosch would design it that way in a million years, so lets assume that it has a fail safe. This would make me assume the issue in this case is with the ABS module either mechanically failing or getting the wrong commands because of the underlying 12V issue.

I admit I don't understand the exact implementation but I'm pretty sure all the force of the brake pedal is transmitted to the master cylinder even if the gears are fixed.

 

[DrSmile]

Based on that picture I bet that something like a gear broke and got in the way of the piston being able to move. Let's hope that's a rare occurrence.

 

[Timbo2]

Blended regen requires an additional module that goes inline with the brake lines.
ESP® hev

Plus in typical Tesla fashion they can suck some cost out of the car.

 

[Daniel in SD]

Based on that picture I bet that something like a gear broke and got in the way of the piston being able to move. Let's hope that's a rare occurrence.

I think the rod slides all the way through the gear. The assist adds force, it doesn't gate it.
The most likely explanation is that OP simply did not press hard enough to feel the brake working over the already significant regenerative braking.

 

[Sophias_dad]

I think the rod slides all the way through the gear.

Yes, note the spiral cutting on the mainshaft, and GIANT bearings to the right of the big gray gear. When the gear is turned by the motor, the gear pushes the mainshaft due to the spiral.

To get the pedal to work without the brake motor turning, I could imagine there's actually a concentric shaft, where the outer portion of the mainshaft is threaded, and there's a hidden interior shaft which can feed-through the motorized shaft. The threaded area of the mainshaft to the left of the gray gear seems to be much larger(and has a large black axle beyond the threading), while the stuff actually attached to the pedal to the right of the gear is a relatively narrow silver rod.

 

[Raro]

Blended regen requires an additional module that goes inline with the brake lines.
ESP® hev

I admit I don't understand the exact implementation but I'm pretty sure all the force of the brake pedal is transmitted to the master cylinder even if the gears are fixed.
View attachment 595853

Yes im sure there is a fail safe, how much harder would it be to push, not sure!