Low speed brake "grind"

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Johnstecz, Jun 3, 2022.

  1. Johnstecz

    Johnstecz New Member

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    My daughters 2005 Prius has a disconcerting low speed brake issue. The brakes feel good and smooth at higher speeds regardless of gentle braking or braking hard.

    However, when we reach a speed threshold (not sure what the threshold is, but ~5mph. But from there, the brakes feel very grabby, there is a vibration and noise. It almost feels like the ABS is activating, but I don't lose braking power. When you creep forward (never lifting off of the brakes), you can consistently feel it.

    I replaced the front pads and rotors about 5k miles ago, so I inspected them, the pads and rotors look great, so nothing physical with them.

    I took the rear drums off and on the right rear drum had grind marks on the shoe and drum like there was sand or something in the drum (basically shiny "scratches" on the rotor and shoe). I have ordered new shoes in case that is the issue.

    Part of my troubleshooting issue is that I'm not sure of the hybrid operation. When you press the brakes, is it increasing regen for braking (until you reach some braking threshold). Because there is this cutoff speed where the problem occurs and doesn't occur.
     
  2. bisco

    bisco cookie crumbler

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    yes, the computers apply both regen and brake pressure in most situations. the harder you press the pedal, the more friction braking and less regen. down to around 7 mph, then no regen.

    this transition point throws many people off, and can even feel like the car is shooting forward if you're on rough terrain, even though it is still slowing down.
    prius brakes are typically very grabby at low speed, and rust can build up on the rotors increasing the problem.
    putting it in neutral once in awhile arond 30mph and gentle braking will clean the rust off.
     
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  3. Johnstecz

    Johnstecz New Member

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    ok, thanks for that, we have some good hills in my neighborhood, so I'll give the friction brakes some exercise.

    By the way, the front brakes have zero rust. They are new good quality (powerstop) rotors (they aren't drilled and/or slotted).
    Sounds like replacing the rear shoes with good quality parts will help.
     
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  4. Johnstecz

    Johnstecz New Member

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    I did some braking from 30/40 down to zero while in neutral and it did make a (probably temporary) difference. I still get the low speed judder, but it's less. I'm just going to call it a quirk of the car. (and still going to replace the rear shoes.
     
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  5. Johnstecz

    Johnstecz New Member

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    Well, the problem isn't resolved... A couple of things, I had my wife roll down the driveway in neutral and I watched her stop, you can definitely see the brakes "judder" as it stops. Also, the driver's side wheel has tons of brake dust compared to the passenger side.
    I removed the wheel again and removed the brake pads/caliper, etc. The disks look good, the pads look good. I sprayed them down with brake cleaner and reassembled. It did seem to reduce the problem for a short period.

    I'm beginning to think that the pads or disk is defective in some way (most likely the pads). Like the pads are contaminated in some way (they don't look it).

    The annoying part is they are only a few months old.

    Can you think of anything else that would cause this? It feels like there is "stiction" between the pad and the rotor. It's not a warped rotor, that feels very different than this.
     
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    Does the "slip" light come on the dash (ie, ABS is operating?) If not then it sure sounds like something is up with the pads.

    Posted via the PriusChat mobile app.
     
  7. ttou68

    ttou68 Active Member

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    Just a thought that may not be related...

    Have you check the slide pins, they maybe stuck..

    Posted via the PriusChat mobile app.
     
  8. Johnstecz

    Johnstecz New Member

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    No ABS issues, no lights...

    I was doing some general research and found some info that pointed me toward the slide pins. I'm going to check that out in the morning.
    I guess I'll just take those apart and grease them up and see if that fixes things.

    Thanks for the pointing that out.
     
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  9. xliderider

    xliderider Senior Member

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    Don't lubricate the brake caliper slide pins with regular, petroleum based grease though. It will degrade the rubber seals and dust boots.

    Use a lithium soap or silicone base grease that won't break down or swell the rubber seals and dust boots.

    Posted via the PriusChat mobile app.
     
  10. Johnstecz

    Johnstecz New Member

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    I checked out the calipers on both sides, pins on the drivers side were fine, (where I'm getting all of the brake dust), but I regreased and greased the edges of the pads where it contacts the calipers. I also did the same on the passenger side, pins were a bit sticky on that side, so regreased, etc.

    Initially, it seemed must better (car/brakes, etc at ambient), then as I drove a little bit, the vibration came back, but much less.

    Now, I'm beginning to think it might be ABS/TC related. (although I don't have a light). If I creep really slow (like 1 mph), the vibration sound, although much reduced seems to be at the same frequency as at 4mph, anything above that, it the issue doesn't manifest itself.

    Since I'm getting so much brake dust on the one side... Could the ABS/TC be pulsing the driver's side caliper (like adding pressure, not releasing), although this doesn't totally make sense, since I'm not on the gas. It definitely doesn't feel like ABS activating where you don't get the braking power you expect (like on ice). Anyone know of any logic in the ABS/TC that changes at about 4-5 mpg?
     
  11. dolj

    dolj Senior Member

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    At 7 MPH the regen stops and transitions to 100% hydraulic braking.

    If you are getting a rumbly noise and/or shudder when less than 7 MPH I wouldn't worry too much. Just consider it an alarm to alert pedestrians who have lost all situational awareness.
     
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  12. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    More likely you've just got some transient build-up related to the unequal pressure from sticking slide pins.

    Drive more. Do a few hard brake applications to help scrub down any inappropriate build-up and let the pads develop a new face on the rotor. Do not expect instantaneous results, but keep track of it. Now that the pieces are back to articulating the way they should, it will take a few miles for everything to find a new equilibrium.
     
  13. alftoy

    alftoy Active Member

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    Suggested to bed pads and rotors after installation. This is the procedure for my coated rotors. May be different for your brand.

    If you’re forced to a stop during deceleration, either shift into neutral or give room in front so you can allow the vehicle to roll slightly while waiting for the light. The rotors will be very hot and holding down the brake pedal will allow the pad to create an imprint on the rotor. This is where a judder can originate from.

    How to: Break-in Your New Evolution Coated Rotors - PowerStop Brakes
     
  14. dolj

    dolj Senior Member

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    If you stopped from a high speed in 'N' then that could be the case. In a Prius, the rotors will likely be relatively cool.
     
  15. Johnstecz

    Johnstecz New Member

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    well... I drove the car to a friends house, when I started it to return, the brake, TC and ABS lights lit up. When I got home, I smelled hot brake.... on one side the rotor was about 300 degrees and on the other the rotor was 100 and something.

    The weird part is that I don't think the caliper is sticking. when I was messing with the slide pins, I was able to push the piston back into the caliper.

    So now I'm assuming it's the brake actuator. (very bad news). I guess the good news is that what I payed for the car last year, plus the brake actuator is still cheaper than what it would cost to replace the car.
     
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  16. ChapmanF

    ChapmanF Senior Member

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    I would be slow to assume the actuator for an issue like that. You would essentially be assuming that it is applying fluid pressure on that side when you aren't braking. It should be pretty easy to do sanity checks on that assumption, say by cracking the bleeder open on that side (while you aren't braking) to look for any sign of the unwanted pressure you'd be assuming was there.

    I was in a similar situation once, and even bought a couple electronic pressure transducers, and adapter fittings to mount them at the bleed-screw holes, so I could chart any pressures there while driving (without braking) and catch them in (what I thought was) the act.

    That would work, if there's ever a situation where it's really needed. But in my situation, I was overcomplicating things. I had a caliper without the proper piston return.

    I also tend to pay more attention to things like that, and to the "fitting kits" (those springy, Teflon-coated clips that hold the ears of the pads) than to the slide pins. I just did my usual every-tire-rotation brake inspection, and just as I have always found, all eight slide pins were just fine, no reason even to remove them. The rear fitting kits, though, needed replacement again, and for the second time since I've owned the car.

    My recommendation is to just look at the whole system of caliper, mount, clips, pistons, and slides, and check everything for doing what it's supposed to, and attend to whatever isn't. If you find a pins problem, fix it, but in my experience that's not nearly as often as you'd think from reading PriusChat, where you'd almost think they're the only parts of the brakes.
     
  17. Johnstecz

    Johnstecz New Member

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    What I've checked:
    - Driver's side brake piston can be pushed back into caliper
    - slide pins all lubes and caliper slides on bracket easilty
    - brake pads move on anti-rattle hardware easily (also lubed with brake caliper grease)
    - When I drove home from my friends house, I took the temperature of the calipers and rotors and the driver's side was easily twice as hot as the passenger side.

    I was beginning to think a bad caliper, but changed my mind when the dash lit up with the Traction control/abs/brake lights.
     
  18. ChapmanF

    ChapmanF Senior Member

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    Ah, dash lights! Do you have the codes yet?

    When I had the caliper with zero piston return, the piston could be pushed easily enough in and out by hand. It just lacked that expected 0.3 mm or so of natural return that its rubber seal normally gives it when the pressure is let off.

    That was when I made my resolution to always check new or rebuilt calipers for that before mounting them on the car.
     
  19. dolj

    dolj Senior Member

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    The repair manual does not call for any lubrication of the points where the pad sits in the front disc brake pad support plate (which sits in the caliper bracket) as these have a Teflon coating that should provide a slick enough surface on which the brake pads can slide. If this is what you meant by 'anti-rattle hardware' then that should be cleaned off both the pad ears and the pad support plate.

    I used to grease the support plates as I thought I read in the manual that some special Toyota grease (Brake Caliper Grease p/n 08887-80609) should be applied, but I think that was in relation to a special service campaign to address squeaky brakes in a different model of Toyota and is not applicable to Gen 2 Prius.

    There should be a small amount of brake shim grease (not the Lithium soap base glycol grease used for the slide pins, nor the above-mentioned brake caliper grease) used on the face of the anti-squeal shim that faces the back of the pad. Normally this is supplied in a 5 g sachet (p/n 08887-80409) as part of the anti-squeal shim kit and is freakishly expensive to buy on its own, (like US$25 per sachet). Most will use copper anti-seize for this purpose if they run out of the supplied grease.
     
  20. ChapmanF

    ChapmanF Senior Member

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    The slick coating eventually wears off those clips, at which point, if you're not replacing them, a little grease might be better than nothing. Or maybe not. Toyota would just have you replace the clips with new slick ones. (I think they frown on grease there because it's so exposed, and would just collect grit.)

    I just did some rear brake work including shims, so I got that little sachet of shim grease. It comes with a SDS that identifies it as Molykote AS-880N, if that means anything to anybody.

    "Good water resistance" is an understatement. Just try to wash that stuff off anything. Guess that's why it stays on the shims.
     
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