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2012 prius v hard braking shudder

Discussion in 'Prius v Main Forum' started by archibald tuttle, Apr 27, 2019.

  1. archibald tuttle

    archibald tuttle Junior Member

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    in any other car i would definitely put this down to warped rotor. 85,000 miles. brake pads about 10,000 miles ago. no visible run out. maybe i'm feeling a little tight spot when i rotate the hub. the pads are evenly worn maybe a 3/4 life left. caliper pins slide fine. no particular long downhills or heating of brakes that I would have thought would have caused a warped rotor.

    i can definitely recreate the effect with the car on jack stand powering it at 12 to 15 mph and applying brakes with med. force. mechanic helping me check this out noted that the vibration seems to be in or transmitted to the CV axle toward the tranmission end. the axle is physically tight, not over worn. this seemed odd to him and he's cked a lot of brakes in his life but this problem started marginally and then got more serious as time wen t by and seems to be a classic symptom of rotor warp.

    While I don't think it likely and don't experience the symptom with light breaking and regenerative indication on the dash, I'm just thinking outloud whether there is any regenerative braking mode or CVT operation that could somehow propagate a braking shudder. Looking for any experiences while i'm waiting for a new rotor and a runout gauge. The cheap rotor spec appears to be 4 thousandths or under of runnout, or I can spend twice as much for one speced to 2 thousandths. My guess is that it takes a fair number of thousandths to produce the kind of shudder we are now experiencing. But I'm open to hearing whether my brake pads and rotor life are going to double with the doubly expensive rotor before i make that call. thanks

    brian
     
  2. Air_Boss

    Air_Boss Senior Member

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    Braking is via MG harvesting of kinetic energy, unless you wail on the pedal, which applies the friction brakes. If the shudder is felt on the half shaft, could point to a CV joint.
     
  3. jzchen

    jzchen Newbie!

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    Seems counter to my understanding of how the system works. Upon light braking, no shudder is felt. This is during regenerative braking ONLY, meaning your brakes are not being used at all, only the Motor Generator is being used in Generator mode to produce electricity. Hard brake application quickly overtakes the generation capacity on a Prius because of it’s small battery and weak MG, when the brakes are hence applied.

    Hoping that the new brake parts that are on their way solve this issue for you. Interestingly, on the original rotors and pads, when my parents back the v out in the morning after releasing the parking brake there is a nasty squeak squeak squeak squeak... upon shifting to D this tends to go away, only to come back next morning again. (v has less than 25k total miles last I checked, I’ve been checking more as to take it to have the tires rotated at 25k miles)...
     
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  4. archibald tuttle

    archibald tuttle Junior Member

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    airboss, so there does not seem to be a lot of looseness in the CV axle. my best estimate is that maybe if I have runout on the brake rotor this is telegraphing to the CV axle because of the shudder from the brake because the free wheeling is at the transmission end and the CV axle is 'hard' connected to the rotor. I have experienced the same thing jzchen and others report which is 'morning grab' of the pads, the sticky squeal as you back out first thing but otherwise wasnt' aware of any braking the would have heated the rotor and this problem was nonexistant after relatively recent brake pad replacemnt (10 ,000 miles) started lightly maybe 4 or 5 thousand miles ago and then got worse so it reads like a bad rotor. Few days still to go and I'm hoping that even modest price replacement will be within spec enough to immediately show whether that was the problem.

    absolutely right jzchen on regnerative braking which just doesn't seem to cause any issues. its parked for now and couple days more i'll have rotor.

    I'm just bumping the thread to see if anybody has had a hard braking only shudder that was not a runout rotor. Related question, i still can't really tell how the B function on the transmission is to be used. I'm assuming maybe this was added because the CVT transmission doesn't provide the same ability to use the engine as a brake (separate from the regenerative braking) or is it just a way to set regenerative braking without stepping on the pedal or both. I'm used to an engine brake switch on a truck but trying to figure out what this one does and optimal strategy for employing it.

    thanks,

    brian
     
  5. ChapmanF

    ChapmanF Senior Member

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    B is essentially a way to tell the car that you're at the top of a long downhill that will yield more energy than the battery can store.

    If you take the downhill in D, the car will follow its usual strategy of capturing as much regeneration as it can, filling up and heating the battery early in the descent, and then have to use engine braking and friction the rest of the way down.

    If you switch to B at the top of the downhill, the car will know to capture regen at a lower rate, filling the battery more slowly and keeping it cooler, while making more use of engine braking and friction (and again, using those methods exclusively the rest of the way down once the battery is full, which should happen further down the hill).
     
  6. Air_Boss

    Air_Boss Senior Member

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    "Morning grab" is simply friction surface oxidation, except under the pucks, so that spot will be clean(er).

    On the CR-V we had an episode of intermittent front brake shudder associated with tire belt separation.

    I would still vote for sticky/worn CV joint over rotor warp/runout.