Two brakes per rear rotor

[smorgasbord]

I just stopped by the Santana Row store for a quick visit. I noticed the black Model S there has two disc brakes per rotor.

I think the Roadster's brakes aren't quite up to the task of spirited driving. With a weight of 4000lbs, Model S needs good brakes, but I wonder why they didn't beef up the fronts instead?

 

[brianman]

Related...

What time is it? NAIAS TIME! | Forums | Tesla Motors

Discoducky
Ask what the second calipers are for on the rear brakes. Pretty sure they are the parking brake, but it would be good to know for sure as I don't want to be replacing two sets of shoes for the rear disc's.

Douglas3
I asked a Tesla engineer about that at the factory tour. The second caliper is indeed for the parking brake. It's electrically actuated and automatically engages when you put the car in Park.

 

[TEG]

Yes, I heard the same thing. Most cars I know have a cable that can actuate the main calipers for "emergency brake", but for some reason the S has a small slave caliper for that.

 

[Albern]

I can't recall other cars except the McLaren F1 that actually have a second set of calipers.

I wonder if by making the parking brake electronically actuated we'll loose the function of emergency braking. What's the alternative if the braking system suddenly shuts down?

 

[Doug_G]

Related...

What time is it? NAIAS TIME! | Forums | Tesla Motors

Yeah, I'm Douglas3 on the Tesla forums. The main calipers are hydraulic, and the second, smaller brake shoe is actuated by a fairly beefy looking electric actuator.

It seems very unlikely that you would lose both the hydraulic systems and the electronic systems simultaneously.

 

[TEG]

Pictures, videos, and news from the Model S (pre-)event Oct 1, 2011

Interesting factoid

There are two calipers on the rear wheels. At upper right is the electrically activated parking brake, which engages automatically when you put the car in park. The larger hydraulic brake caliper is on the left.

 

[goyogi]

Is that a brake dust shield that's stamped with the letter T?

 

[TEG]

The letters T|E|S|L|A go around that plate as I recall (not just a T).
I think they call it a spash guard to keep road debris from striking the brake rotor. So not so much to keep brake dust in, but rather to keep contaminants out.

 

[WarpedOne]

Yes, I heard the same thing. Most cars I know have a cable that can actuate the main calipers for "emergency brake", but for some reason the S has a small slave caliper for that.

All these components are bought from part suppliers. Maybe all existing brake calipers with built in "parking brake feature" aren't strong enough for S? ICE cars have bigger brakes in front, S is an exception for having really big brakes in the rear.

 

[GSP]

Yes, I heard the same thing. Most cars I know have a cable that can actuate the main calipers for "emergency brake", but for some reason the S has a small slave caliper for that.

It is common for cars with 4-wheel disc brakes to use small cable actuated drum brakes in the rear for the parking brake, instead of using the main calipers.

Also, it it interesting that the Model S uses fixed calipers, instead of the cheaper, and much more common, floating calipers. This is going to be a GREAT driver's car.

GSP

 

[TEG]

Tech Feature: Electric/Electronic Parking Brakes.

MOTOR Magazine Article | MOTOR Information Systems

...Vehicle manufacturers are looking for ways to reduce weight and enhance vehicle safety systems. One system that’s seeing wider application is the electronic parking brake system. Audi began using this on the 2004 A8, and it’s now standard on all 2009 Audi vehicles...

 

[TEG]

Apparently (retrofit?) on some Honda/Acura NSX as well.

 

[TEG]

Dodge Viper:

 

[Cal1]

Are the pistons on both the main caliper and the e-brake solenoid driven? No hydraulic fluid? If there is one where is the master? If we lose power on a hill will the e-brake disengage, letting it just roll?

Cal

 

[Doug_G]

Are the pistons on both the main caliper and the e-brake solenoid driven? No hydraulic fluid? If there is one where is the master? If we lose power on a hill will the e-brake disengage, letting it just roll?

The e-brake is electrically driven, but is NOT a solenoid. That would not make any sense at all, as it would (a) be unsafe and (b) would consume too much power.

It sounds like an electric motor when it engages/disengages, so I'm pretty sure that's exactly what it is. You do not have to worry about your car rolling away.

 

[Newscutter]

So in the event of a catastrophic brake fluid leak--- could the parking brake be used at the emergency brake and stop the car? In a regular car there'd also be downshift options but even with regen that might not be fast enough (like downhill).

 

[jerry33]

So in the event of a catastrophic brake fluid leak--- could the parking brake be used at the emergency brake and stop the car?

Yes. Press and hold the Park button and the parking brake will engage.

 

[Cal1]

The e-brake is electrically driven, but is NOT a solenoid. That would not make any sense at all, as it would (a) be unsafe and (b) would consume too much power.

It sounds like an electric motor when it engages/disengages, so I'm pretty sure that's exactly what it is. You do not have to worry about your car rolling away.

So how is it exactly engaged? Gotta be something actually pushing the pistons to pinch the rotors. Unlike the actual brake calipers I don't see any brake bleeder valves.

 

[Doug_G]

So how is it exactly engaged? Gotta be something actually pushing the pistons to pinch the rotors. Unlike the actual brake calipers I don't see any brake bleeder valves.

I would imagine it's some kind of screw or cam driven by a motor and gearbox.

 

[tezco]

I would imagine it's some kind of screw or cam driven by a motor and gearbox.

On the Leaf you can pull once to activate emergency brake and pull a second time if you need more stopping action.