Park or parking brake issue?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Sep 8, 2021.

  1. pasadena_commut

    pasadena_commut Active Member

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    Today I parked our 2007 facing downhill in a parking lot with a pretty good slope. I didn't measure the angle but by eye the front of the car was at least a foot lower than the back. Anyway, pulled in facing forward (and downhill) with my foot on the brake, set the transmission to Park, set the parking brake, turned the car off, then released the brake pedal. When my foot came off the brake it rolled forward about 12-18 inches before it stopped on its own, without having to step back on the brake. Never had a car do that before, is it normal?

    There was no problem backing out of the sloped parking slot: foot on brake, start car, put transmission in reverse, release parking brake, release brake (it did not roll forward here or at any previous step), apply gas (backed out normally).

    The other thing I have noticed about this car is that when it is parked in the driveway (very slight slope with the back of the car lower) in Park and parking brake set, if I get in the car and shake it back and forth there is a sort of weak banging sound, like a piece of metal is hitting a rubber stop. Always assumed that this was the car being pushed forward a couple of millimeters by the shaking and then rolling back onto some sort of stop in the transmission. Again, not something any of my previous cars did.
     
  2. bisco

    bisco cookie crumbler

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    prius has a lot of roll before the parking pawl kicks in, but sounds like your emergency brakes need work.

    the sound you hear when rocking it is normal.

    try leaving it in neutral on a similar steep slope, and see if the e brake will hold it.
     
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  3. davecook89t

    davecook89t Senior Member

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    If putting the car in Park before setting the parking brake is the normal sequence you use when parking, I think you should change that sequence. It would be preferable to set the parking brake before putting the shift lever in Park, to ensure that the brake is providing most of the resistance to rolling, rather than the pawl. If it really rolled forward 12 to 18 inches, I would question whether the pawl is even functional at this point.
     
  4. ChapmanF

    ChapmanF Senior Member

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    In my usual order of things (and also as described in the OP), the right foot stays on the service brake pedal until after both the parking brake and the parking pawl have been set. So in most cases, releasing the service brake in the last step transfers the load over to the parking brake (which has negligible free play), more than onto the parking pawl (which has a bit of play, though I believe the play within a notch is not as much as 12 to 18 inches*).

    The description mostly sounds to me as if the parking brake is not holding well. As described in the OP, the parking brake was already applied, but on releasing the service brake, the car rolled anyway, until stopped by the pawl.

    As it is a Gen 2, I wonder how well adjusted the rear brakes are. They have a self-adjusting mechanism that depends on regular, routine use of the parking brake (as described here and yes you can quote the 0.03 mm). If they get out of adjustment, the parking brake will hold poorly. If you do routinely use the parking brake and they still seem poorly adjusted, it's possible for the adjusters to be gummed up, which can be examined by popping the rear drums off. (People often intuitively look for the nuts to shorten the length of the parking brake cable, but "cable stretch" shouldn't be on the short list of suspects, unless Sasquatch has been driving the car.)

    * The parking pawl drops into notches in a sturdy wheel inside the transaxle. Once it has dropped into a notch, I don't think the car has anything like 12 to 18 inches of fore-aft travel. But every now and then, just with luck of positioning, when you parked the car, the pawl may have set down right on a high spot between notches. Then, if the parking brake isn't holding it, the car may roll a bit further before the pawl drops into the next notch and stops it. I think you will find, once that has happened, you won't have as much as 12 to 18 inches to roll the car back the other way.
     
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  5. pasadena_commut

    pasadena_commut Active Member

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    OK. That is the parking pawl in the transmission.?

    That is a good idea. There are some hills nearby.
     
  6. bisco

    bisco cookie crumbler

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  7. mr_guy_mann

    mr_guy_mann Active Member

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    When you set the parking brake, stomp the pedal hard. Then see if it will hold the car, either on hill in neutral, or in drive on a flat road. I prefer to have it set so that I notice the drag if I try to drive with it still engaged.

    Posted via the PriusChat mobile app.
     
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  8. pasadena_commut

    pasadena_commut Active Member

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    Ended up testing this on a parking garage down ramp before the mall opened. I eyeball estimate that slope as about 20ft/140ft or 1:7 which is about 8 degrees. The parking brake did not hold in neutral on that slope no matter how hard I pressed down on it to set it. Note, I did not leave my foot on it, just set it and then lifted my foot off. I tried setting and releasing it three times and it didn't seem to make any difference, so perhaps the adjusters are not working.

    I also tested setting Park and the parking brake several times, and it never rolled more than about 6 inches before stopping.

    The car was bought used, so I cannot speak to the size of previous drivers, but I'm not a big guy, so a stretched brake cable wouldn't have resulted from anything I did.
     
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  9. ChapmanF

    ChapmanF Senior Member

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    Yeah, getting the drums off and checking the condition of the shoes and the motions of the adjusters would be my first move. I would generally dismiss the idea of a stretched cable unless and until I was sure the adjusters were working and the clearance was correct and the parking brake was still ineffective.

    Sometimes the adjusters can be gummed up and difficult to turn. Sometimes you will notice where one tooth, or a couple teeth, of the star wheel will have had the point rounded off, by the adjusting lever sliding up and down over it endlessly and never actually turning it. (If that happens, the adjusters have to be replaced, They're very inexpensive.)

    The adjusters on the right and left sides of the car are mirror images, and if anyone worked on the rear brakes before and got them swapped, their "adjustment" action will be to loosen the brakes!
     
  10. pasadena_commut

    pasadena_commut Active Member

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    Verified that the parking brake is strong enough to keep the car from creeping when in drive. Tried to force the brakes to adjust by putting it in park and then alternating between the parking brake (set/release) and the brake (press/release). Now I have to go back to that parking garage ramp to see if it made any difference.

    A few months ago I drove a couple of blocks with the parking brake on. Perhaps that glazed the drum and/or pads, so that the adjustment is right, but the amount of drag is too low?

    If the star gear has a rounded off tooth where does one obtain a replacement? I didn't see that part mentioned with that name in the brake or parking brake parts diagrams in the Toyota dealers online parts sites.
     
  11. ChapmanF

    ChapmanF Senior Member

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    Hmm, looks like it's the strut kit, rear brake, containing the adjusters, struts, and upper return springs for both sides (04943A here). Ok, that makes it a bit less inexpensive than I was thinking for adjusters by themselves. Star wheels shown in the middles of the struts; they just don't look very toothy in the drawing.

    [​IMG]

    Glazed surfaces can definitely happen, and some 150 grit wetordry sandpaper and some elbow grease can easily make them unglazed again. Best done wet to keep dust down.

    More care is required doing that with shoes than with disc brake pads. For pads you can put the sandpaper on a flat surface and scrub the pads around on it, and they stay flat. For shoes, be careful you're only after the shiny glazed layer and try to avoid changing the curvature of the surface, or it won't uniformly meet the drum. (If you get it just a little off, it should wear back into the right shape sooner or later, but still something to think about.)
     
  12. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Between these 2 Repair Manual excerpts you should have what you need, though I see there's some orphaned ref's.
     

    Attached Files:

  13. pasadena_commut

    pasadena_commut Active Member

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    I finally got around to retesting the parking brake, after forcing it to adjust (in theory) by many cycles of set parking brake, release parking brake, step on brake, release brake all while in Park. As before this test was "parking brake only while in Neutral" on the 2nd to 3rd floor ramp at the Westfield Santa Anita North parking structure. It held this time. However, it slipped slightly on the 1st to 2nd floor ramp, which is just a bit steeper. On that steeper ramp the car started to roll immediately, but at a snail's pace, like 1 mph, and stayed at that speed for around 20 feet, without noticeable acceleration. Now I'm wondering if one or both of the drums isn't just packed with brake dust, and that is interfering with the adjuster.
     
  14. ChapmanF

    ChapmanF Senior Member

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    Have you had the drums off yet to see?
     
  15. Mendel Leisk

    Mendel Leisk Sand Pounder

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    A couple of M8X1.25** bolts say at least 1" threaded length, will help with the drum removal, if they're stuck on. There's (compatible) threaded holes in the drum: screw the bolts in* till they're pressing against the hub behind, then back and forth, screw them in further, to break the drum loose. Some hammer taps on the side of the drum might help, as you go.

    * The threaded holes will likely be rust, requiring you to screw them in, then back out, blow out the dust, repeat, to finally get the bolts right through.

    ** Readily available at most hardware stores these days. Or Amazon.
     
  16. pasadena_commut

    pasadena_commut Active Member

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    "Fixed", in that it now holds on the steepest grade, but I cannot say definitively why it works now and did not before.

    Yesterday my son was around to help so we pulled the back wheels and the drums. The first problem was that my 3 ton jack stands are a little too wide for this Prius. If the slot is centered on the pinch weld the outer part of the jack stand pad sits on a chunk of black plastic which lines the outside of the underside of the car, inside a sort of channel. These look like they are there for aerodynamics. This is strange, all the cars I have worked on previously the pinch weld in the jacking location was the lowest part of the car in that vicinity, and the jack stand pad would sit on a metal surface on one side or the other when centered on the pinch weld. Anyway, put it in park, rolled forward until it hit the transmission stop (driveway has a slight slope), then put chocks in front of the front wheels, placed the floor jack under the rear center jack point, lifted it then lowered the car onto the stands (anyway), then lifted it slightly (1 mm?) so that it was still on the stands but most of the weight was on the floor jack. Not very safe, but we were not going under the car. Pulled the cap up slightly on the brake master cylinder, to release any vacuum or pressure that might have been there.

    Spun the rear wheels with the parking brake off. For the same slight push one spun exactly 1X and the other 1.5X turns.
    Removed the rear lug nuts easily with an impact wrench and pulled off the wheels. Removed the driver's side drum with some light taps from a rubber mallet. The passenger side drum would not budge that way, but came off eventually using the M8x1.25 bolts. It took quite a while to get the bolts in because the threads were coated with dirt and/or rust. When the drums came off about the same amount of brake dust fell out of both of them (onto newspaper, which was then sprayed with some water to keep the dust in place.) Nothing blatantly wrong with either side: no broken springs, the shoes moved in and out with the parking brake, no glazing of the pads (about 3mm thick), the inside of the rotors looked more or less like the swept area on a disk brake, the rubber plugs behind the star gear were present on both sides. I didn't have any brake cleaner so dislodged as much dust as possible with a hand pump basketball inflater. Then ran away and let the dust settle. I was wearing a 3M P100 respirator which kept the dust out of my lungs but also wasn't compatible with wearing glasses, so I couldn't see up close very clearly. The star gear did not look worn to me (but it was a little blurry), and my son thought the two gears looked about the same.

    We took a video of the hand brake working on each side with the drum off, but it may be too big to post here. Something squeaked on each side when it was moving, but I was in the cab so could not say what. I don't hear that squeak when using the parking brake normally, which isn't saying much, because my hearing sucks at high frequencies.

    Put it all back together, torqued the lug nuts down. Brakes worked and felt the same. The parking brake was maybe stopping a tiny bit further from the floor than I recalled, but that could be my imagination. Forced brake adjustment, again, with 5 rounds of: parking brake applied, parking brake released, step on brake. Took it to the same mall parking lot and tested it again. The parking brake held on the steepest slope this time in neutral.

    So, if I "fixed" anything it was probably by releasing some brake dust, lodged somewhere, which was somehow interfering with the mechanism.
     
  17. pasadena_commut

    pasadena_commut Active Member

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    Let's see if the videos upload. Sorry about the moving view, we didn't have a tripod. First one is the driver's side. Hmm, it will not take an MP4. Put them both into a .zip but 26.2M was too big. How do people upload videos for this site?
     
  18. bisco

    bisco cookie crumbler

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    youtube for one
     
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