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2nd caliper on rear brakes

Discussion in 'Model S' started by Footbag, Jun 15, 2015.

  1. Footbag

    Footbag Member

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    This might be a dumb question, but... what is the 2nd caliper for on the rear brakes (P85D if it matters)? I've had many people ask, but I keep forgetting to find out... and this forum seems the best place to confirm an answer! I'm guessing it might be the parking brake?
     
  2. Max*

    Max* Autopilot != Autonomous

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    It's the parking brake.
     
  3. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Don't forget to clean it from time to time! (Drive 50 mph, put gear in N, push and hold the P-button on the stalk: let the parking brakes take the car down to almost a standstill).
     
  4. morbot

    morbot Member

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    I was under the impression that the 2nd caliper on the rear tires are the regenerative breaks? Never had it confirmed though.

    This doesn't seem like a good idea.
     
  5. murphyS85

    murphyS85 Member

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    Regenerative braking is done by turning the motor into a generator which charges the battery. It has nothing to do with brake shoes.
     
  6. Majerus

    Majerus Member

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    Why would you do this? The parking brake is always used when the car is put in park , doing this seems like a good way to cause premature wear.
     
  7. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Rust build up.

    And the "regenarative brakes" do not exist per se, regen braking happens in the motor.
     
  8. m6bigdog

    m6bigdog Member

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    Rust on the Parking Brake Pads??? The rear rotor is kept clean by the rear brake calipers and in general Pads don't rust.

    However, on a rainy day it would be a good idea to put some heat into the rotors before you park the car for the night to dry off the rotors and pads as moisture trapped behind the pads can cause some serious rotor rust and that can cause the brakes to judder.
     
  9. Tuan

    Tuan Member

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    A good drill in case of an emergency. I've been ICEd for so long that I would look for the hand brake lever to yank on.
     
  10. Zextraterrestrial

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    sure, pads don't rust but the rotors do and on a wet day they potentially rust to pads. I always do a few runs to dry both the brakes and parking brake after washing my car
     
  11. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Yeah this was my point. I know the surface of the brake pad on the caliper doesn't rust. But if it's only constantly being applied to a rotor surface standing still (parking brake) then you'll risk having an uneven contact patch developing and rust build up (on the rotor) underneath. If you park for a long time, with a wet rotor, you'll sometimes feel the park brake "sticking" a little as you drive off.

    By using it now and then in actual braking you grind up some new, even surface on the pad. It's not like it's ever going to wear out from doing this.
     
  12. m6bigdog

    m6bigdog Member

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    The Tesla has a "Parking Brake" not an "Emergency Brake".
    Also, I have yet to see Tesla recommend the procedure you suggest.

    Sorry, Not Me, I'm not going to fiddling with the gear selector stalk to engage the Parking Brake while the car is at speed, because of a perceived emergency stopping procedure; that is dangerous and I anticipate the regen braking is also disengaged in Neutral...(I'm not going to test if it is or isn't).

    The Tesla as well as every car made, in the US in at least the last 40 years, has a dual master cylinder split brake system that will effectively stop the car should one brake circuit fail and you will get a brake failure warning/indication on the instrument cluster to let you know you should no longer drive the car.

    Besides, the regen braking (your best buddy when it comes to stopping) would not be affected by a hydraulic brake system failure and should the body electrical system fail and prevent regen braking the Parking Brake will not work either.
     
  13. wycolo

    wycolo Active Member

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    Wow, something new to overthink and play with! :love:
    --
     
  14. Cyclone

    Cyclone Active Member

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    While I agree with you on not doing a 50 mph stop using the Emergency Braking Procedure, in all fairness, Tesla calls it an E-Brake on the 17" display.
     
  15. Johan

    Johan Took a TSLA bear test. Came back negative.

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    The secondary caliper system's main function is to act as a parking brake when you park the vehicle. It has a secondary function as well: emergency brake while the car is in motion, by holding the P button pressed. This is well documented in the car manual.

    Regen does not get applied with the car in neutral, for obvious reasons. The hydraulic brakes, be it the primary ones (brake pedal) or emergency system (P button on stalk) work well in both N and D.

    There's nothing wrong with what I'm recommending. However I do agree that my recommendation is based mainly on opinion rather than solid evidence.
     
  16. Zextraterrestrial

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    opinion - cleaner brake pads work better in an emergency situation? I think not
    =fact

    similar to driving long distances or even short distances in really wet weather without needing to use friction braking. the first time you try to use them they won't work. maybe this is different on the newer electric Bosch cylinder brakes but I don't know
     
  17. Johan

    Johan Took a TSLA bear test. Came back negative.

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    True.

    Also: by now and then testing the secondary system I can feel it working, and be sure it will hold the car well if I park on a steep incline.
     
  18. Mphmd

    Mphmd Member

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    wonder if the brake lights come on when applying the e brake if the car is in motion
     
  19. Zextraterrestrial

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    if the negative G force is great enough they should
     
  20. SabrToothSqrl

    SabrToothSqrl Active Member

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    that's interesting because it's all fun and games to wreck a tailgaiter's day by suddenly slowing with no brake lights ;)

    Of course I don't suggest doing that in a Tesla.. but feel free to sacrifice any lesser car :)
     

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