What would cause this brake pad wear, and any guesses about some unusual symptoms?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by MrPete, Mar 2, 2026 at 10:47 PM.

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  1. MrPete

    MrPete Active Member

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    I'm doing a complete 4 wheel rotors+pads replacement on our 2011+ 250k mile prius.

    Rear wheels now complete (rotors were at 7.8mm.)

    Physical evidence of issues:
    * Right rear outside pad has worn flat on the upper (close to rotor edge) side, several mm of differential wear (See photo.)
    * All four rear caliper slider pins had sludgy black grease. They moved but not easily. (Redoing with the official Toyota grease made a night and day difference!)
    * Rotating wheels definitely made a small scraping sound: pads in contact at least lightly.

    In the last month, I noticed:

    * Occasional small vibration while braking
    * The car was outside overnight in very cold weather (0-10F). In the morning, it did NOT want to roll for the first 5+ minutes until warmed up. Scary to me.

    My questions:
    * What could cause the differential pad wear? Could it be the sludgy slider pin grease?
    * Could the grease also have caused the roll resistance, perhaps brakes still acting even though parking brake released?

    Thanks for your insights!

    20260302_202211.jpg
     
    #1 MrPete, Mar 2, 2026 at 10:47 PM
  2. VelvetFoot

    VelvetFoot Active Member

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    What does that mean? The engine warmed up? You're not warming up the brakes, unless you're driving with, say, the parking brake dragging-on one or the other wheel perhaps. That'd cause some wear, lol.

    I'm thinking something's going on with the parking brake. No evidence of dragging, eg, mpgs went down suddenly?

    Is the parking brake action smooth, from the hand lever to the brakes?

    Parking brakes freeze up some times, literally, if they get wet during the day and freeze overnight.

    Not a Gen 3 owner. I've owned some cars, but I'm not a mechanic.
     
    #2 VelvetFoot, Mar 3, 2026 at 9:08 AM
  3. Mendel Leisk

    Mendel Leisk MMX GEN III

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    With the back wheels off the ground, if you give them a decent push, will they free-spin at least couple of turns? See rear brake drag link in my signature.

    (on a phone turn it landscape to see signatures)
     
    #3 Mendel Leisk, Mar 3, 2026 at 11:00 AM
  4. ChapmanF

    ChapmanF Senior Member

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    I don't clearly see in your pad photo what you are trying to show.

    Could it be like what's going on in ➡this post⬅?

    I also found it quite challenging to photograph the pads in a way that showed what I meant.
     
    #4 ChapmanF, Mar 3, 2026 at 11:19 AM
  5. MrPete

    MrPete Active Member

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    Sure is hard to photograph!

    So:
    * notice the pad in back has a slot still, edge to edge. Pad is about 5mm thick, Slot 2mm.

    Now the pad in front :
    * the far edge has the slot. That goes on the inner diameter of the rotor ("down" side when placing the pads) Pad ~5 1/2 mm thick
    * but the near edge has no more slot. 2mm thick pad.

    So,that pad (on the outside/wheel side of the rotor), is worn at an angle?!

    As for the parking brake: I made no adjustments and it doesn't stick. (did not remove or reattach to do the brake job.)

    So far the only major change is properly lubing the pins.
     
    #5 MrPete, Mar 3, 2026 at 12:14 PM
  6. ChapmanF

    ChapmanF Senior Member

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    Ah, so not stepped wear as in my photo, but a flat wear face that is angled with respect to the back of the pad?

    Is that "pad in front" the one in contact with the caliper piston?

    There are features provided (a pin on the back of the pad, and notches in the face of the piston) to prevent the piston from turning as it extends (because a threaded post, internal to the caliper, is a key part of how the parking brake works).

    If the piston didn't stay properly aligned (notch to pad pin) when the brake was last assembled, the pad can end up at an angle because its pin is out of the piston notch, and that angled pad wear is the result.

    Mendel will have more info.
     
    #6 ChapmanF, Mar 3, 2026 at 12:25 PM
  7. MrPete

    MrPete Active Member

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    Correct about the wear. No, this is not the piston side.
     
    #7 MrPete, Mar 3, 2026 at 1:29 PM
  8. Mendel Leisk

    Mendel Leisk MMX GEN III

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    #8 Mendel Leisk, Mar 3, 2026 at 1:40 PM
  9. MrPete

    MrPete Active Member

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    Can't be the piston. One thought going back a few years... I drove a few thousand miles with the out of alignment rear axle. It was bad enough that I wore out a tire VERY quickly. Perhaps it also wore the brake pad and I didn't notice. :(

    I'll be watching the new brakes carefully, and check everything after a few months...
     
    #9 MrPete, Mar 3, 2026 at 2:12 PM
  10. ChapmanF

    ChapmanF Senior Member

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    Very hard for me to picture an alignment problem causing that, as the caliper bracket is mounted to the same flange the hub is. Almost gotta think there was something foreign caught between the outboard pad and the bracket. Or the misalignment involved someone replacing the hub, and getting something foreign beneath its flange? Or when mounting the caliper bracket?

    Still, I think something under the hub flange or bracket would have led to angled wear of both pads. Just one pad still makes me think something was between that pad and the bracket.
     
    #10 ChapmanF, Mar 3, 2026 at 2:50 PM
  11. mjoo

    mjoo Senior Member

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    You can add too much grease to the caliper pins (thinking that more lube is better) and it'll cause the brakes to drag.
     
    #11 mjoo, Mar 3, 2026 at 3:42 PM
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