brakes mildly grabby at low speed in new Prime.

Discussion in 'Prime Main Forum (2017-Current)' started by The Big Sleaze, Jan 19, 2020.

  1. The Big Sleaze

    The Big Sleaze Junior Member

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    Coming up on 1500 miles since brand new. IIRC they were always like this and I wrote it off to regen, but now I hear regen is off at lower speeds.

    Nothing major, but diff from every other car, including total beaters. Even old beaters will have PERFECTLY smooth silky braking all the way from 1/2 mph to stop.

    Should I try burning off rust with series of hard braking (as suggested in 2nd gen thread), or take to dealer?

    Is this common in Prius for some reason?
     
  2. FuelMiser

    FuelMiser Senior Member

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    Common? Yes, but don't know the reason
     
  3. jerrymildred

    jerrymildred Senior Member

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    Not common. Universal. ;)

    Once you get down to about 4-7 mph, there's not enough kinetic energy available for regen braking to be effective. It drops off as the friction brakes get more involved. If the rotors have been exposed to any moisture (and there's always moisture in the air) they are a tiny bit rusty. If you're close to the ocean, they might be a little more than a tiny bit rusty.

    My right foot has adjusted to the the point where I almost never notice it anymore except when I drag the brakes rolling down the driveway in the morning. I really hear it then.

    Different cars have different tendencies to get rust on the rotors. But they all get a little and practically all make that noise starting out the driving day. You notice it more in a Prius because so much of the braking doesn't involve friction that it's more noticeable when it switches to that mode.
     
  4. Salamander_King

    Salamander_King Senior Member

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    I remember my 2017 PRIME when it was new, the brake was mildly grabby at low speed as you described. Everyday when I am driving down my driveway ~50 feet and need to come to a full stop before getting out to the public road, I would be going less than 10mph but when I need to stop with very light braking, it grabbed and jerked. It was quite pronounced and noticeable than my previous Gen3. However, now after 2.5 years, I don't notice as much of this jerkiness. I am not sure if this is due to the brake worn out bit and make it less grabby or I got use to it and not noticing it as much or maybe I am now better at applying even lighter braking now than when it was new.

    There was an old thread describing this phenomenon, but I can't find it now.
     
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  5. jerrymildred

    jerrymildred Senior Member

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    In my case, I'm guessing that it's a combination of all three. ;)
     
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  6. Salamander_King

    Salamander_King Senior Member

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    Yeah, that could well be true for me too.
     
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  7. sam spade 2

    sam spade 2 Senior Member

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    Yes. Common to a LOT of cars, especially when the environment is cold or damp.
    More common with a hybrid because the actual brake pads and rotors don't get used as much.
    My C grabs on the first couple of stops; more noticeable if it has been sitting more than 24 hours.
     
  8. m8547

    m8547 Active Member

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    Mine had grabby braking sometimes, but not usually. It seems to happen after hard braking. Most of the time the brakes are perfectly smooth down to just barely inching forward. But sometimes they get stuck in the grabby mode, which is accompanied by a lot of clicking like a relay clicking. I have no idea what causes it or how to trigger it or make it go away, besides speculating that hard braking causes it. It's not rust because it sometimes happens in the middle or end of a drive.
     
  9. Trollbait

    Trollbait It's a D&D thing

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    With the friction brakes seeing less use, the normal build up of rotor rust may not be getting fully polished off like a traditional car.

    Then the switch from regen to friction can be noticeable. Toyota has been improving the feel of the system since my gen 2, but if this is your first hybrid, it may be more apparent after years of driving other cars.
     
  10. bresna

    bresna Active Member

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    Does the Prime work like the older Priuses where if you put it into B, it disengages regen braking? I used to put my old Prius into B every now & then to run off some rust.
     
  11. jerrymildred

    jerrymildred Senior Member

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    Only if you're in HV mode. In EV it increases regen as long as the battery is ready to accept it (not too full or too hot or cold). Actually, Neutral is a better way to scrub off the rust. Just be sure to put it back in D asap.

    The original question, though, concerns a 2020 2 Eco, which would have the same B mode characteristics as a Gen 2 or 3.
     
    #11 jerrymildred, Jan 20, 2020
    Last edited: Jan 20, 2020
  12. Trollbait

    Trollbait It's a D&D thing

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    B allowed more use of engine braking. I don't think it did anything to the brake system's behavior.
     
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  13. Tideland Prius

    Tideland Prius Moderator of the North
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    I blame the electronically controlled brakes (ECB). Ever since the industry moved to ECB, the last bit of braking has never been smooth for me. I pride myself in stopping smoothly (I’m sure drivers of older vehicles will remember the trick to soften the front suspension rebound to reduce or eliminate the whiplash motion when you come to a complete stop).

    With ECB, they’re not sensitive at the last bit of speed so I’m left with a rougher stop than I like.
     
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  14. jerrymildred

    jerrymildred Senior Member

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    Same here. It seems to work well for me simply easing off a little more and a little earlier as I approach my stopping point.
     
  15. ChapmanF

    ChapmanF Senior Member

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    Also shifting to N for that last few feet, so you're not trying to modulate the pedal against the car pretending to have creep.

    At least I can do that silently with the Gen 3 joystick shifter, so a passenger might not notice. The Gen 1 shift linkage would make an audible clunk, and I seriously spent a few minutes looking at the wiring diagram to figure out how I could make a silent shift-to-N pushbutton to mount discreetly somewhere (maybe down where old high-beam footswitches used to go; I could have treated it like a clutch pedal). Never actually built it though.
     
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