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rear brakes maladjustment

Discussion in 'Gen 2 Prius Technical Discussion' started by yups, Mar 20, 2007.

  1. yups

    yups Junior Member

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    Heads up. Rear brakes might need readjusting to free up drums. I caught it at the 10K check. Don't know how I missed it on earlier checks. Guess I wasn't looking for brake wear then.
    Backed off the brake shoe expansion thigamajig. I had to pry the drum off to spin the adjustment dial b/c its designed to only adjust one way while the drum is on or so I think.
    The 06 rolls better. Bumped mpg up by @5. To early to tell if there'll be more. I wonder if they're coming off the lot with sticky rears and after the 5 to 10 K the shoes wear down enough so there's that noticiable "breakin" that I've read happens to improve overall MPG.
    I also noticed a slight pulsing in the brake pedal at the end of slow stops causing a very, Very minor unsmooth/uneven stop prior to the adjustment, which I put down to a out of round drum. I kept meaning to warranty that, but never quite got around to it. Anyways, thats totally disappeared too.
    She's a super sweet ride now.
     
    #1 yups, Mar 20, 2007
  2. brick

    brick Active Member

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    <div class='quotetop'>QUOTE(yups @ Mar 20 2007, 04:12 PM) [snapback]409138[/snapback]</div>
    You sure that part wasn't the transition from regen braking to friction braking? I get a slight "bump" at 8mph every time. Either way it's interesting that your brakes were out of adjustment. I bet it would be a tough thing to notice unless you get back there and check.
     
    #2 brick, Mar 20, 2007
  3. yups

    yups Junior Member

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    <div class='quotetop'>QUOTE(brick @ Mar 20 2007, 06:44 PM) [snapback]409246[/snapback]</div>
    I'm sure. It went away when I pulled in the shoes. The drivers side was the sticky side. So much so that I had to pry the drum off as opposed to the other side which came off nice and easy as I assume it's suppose to.
    I think the tell tale sign is if the car has a slight on off on off pulsing when braking, noticible when coming to a complete stop( like an out of round drum) and only towards the end of the stop like <6mph. Also, if you've got the time, you can always pull the wheel and see if the drum comes off easily or if it drags significantly.
    I'm really hoping it will be significant a change. It was adjusted towards the end of a tank where we avg not more than 46 mpg. Just with the last two gallons, it pushed the tank avg up to 50. That's going to be a big bonus over future averages. maybe 55 to 60. we'll see.
     
    #3 yups, Mar 20, 2007
  4. tochatihu

    tochatihu Senior Member

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    Removal of the brake drums is aided by screwing an appropriately threaded metric bolt into the 'extra' holes in the drum. Dave Bassage discovered that the spare tire holder-downer bolt is right for this.

    Inside there is a manual adjuster, which if you are very clever you can vary w/o removing the drum. But the average DIY is going to want to look inside anyway.

    The way they're supposed to work is to self-adjust when you apply brakes in reverse. So if you want to make sure you're rolling freely at the next mpg contest, just don't back up after adjusting them.

    Aside from raising the wheels and spinning them, it is pretty easy to detect brake shoe drag after a couple of miles driving. Without it, the drum will not have heated up enough to notice.
     
    #4 tochatihu, Mar 21, 2007
  5. brick

    brick Active Member

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    Hmm. The pulsing sensation does sounds like something I've felt at the end of a gentle stop. I'll have to see if the wheels are warm at the end of my commute this afternoon.
     
    #5 brick, Mar 21, 2007
  6. yups

    yups Junior Member

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    <div class='quotetop'>QUOTE(tochatihu @ Mar 21 2007, 09:15 AM) [snapback]409493[/snapback]</div>
    I think if you have to use anything other than simple pulling with your hands, its too tight: The shoes are placing too much pressure on the drum to inhibit release. I'm not so sure about the self-adjusting. Is that reverse concept out of the repair manual? The looks of the assembly reminds me of VW, where you take the slack out by turning the adjuster while the drum is on and finish by using the ER brake. The ER brake lever in the drum ratchets the adjustment cog and you're done. The ER brake should only add tension to the shoe assembly if there's alot of clearance btwn the shoe and drum.
     
    #6 yups, Mar 21, 2007
  7. tochatihu

    tochatihu Senior Member

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    <div class='quotetop'>QUOTE(yups @ Mar 21 2007, 07:44 PM) [snapback]409949[/snapback]</div>
    Another source of friction keeping the drum on the brake mechanism is rust in the middle. This needs to be overcome even if the shoes have clearance.

    As far as the self-adjustment being done by application in reverse or by the parking brake cable. I admit that I have not read a Toyota document specifically describing it. But I am familiar with this design from other vehicles, and to me, the Prius drum brake mechanism exactly resembles this design as shown at:

    http://auto.howstuffworks.com/drum-brake2.htm

    It may however be adjusted as you propose, and perhaps we can hope to receive an official answer on that.
     
    #7 tochatihu, Mar 22, 2007
  8. galaxee

    galaxee mostly benevolent

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    the prius' brake system self-adjusts using the parking brake. unfortunately, said "self adjustment" isn't always enough. periodic manual adjustments may be needed.
     
    #8 galaxee, Mar 25, 2007
  9. yups

    yups Junior Member

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    <div class='quotetop'>QUOTE(galaxee @ Mar 25 2007, 10:02 PM) [snapback]412096[/snapback]</div>
    Thanks G, I almost went out there to find out. That need to know thing... anyways, looks like only a few xtra MPG for this tank, which very well could be just a fluke, but it is the highest ever for us:48+/-. At least the pulsing is gone or next to nothing.
    thanks all
     
    #9 yups, Mar 27, 2007
  10. galaxee

    galaxee mostly benevolent

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    at 28k we got some new tires and while DH had the wheels off the thing, he cleaned and checked adjustment on those rear drums. passenger side was in perfect adjustment (i use the parking brake a couple times a week) but the driver's side was way out. strange. he readjusted that one and knowing him, he'll re-check them when he rotates the tires next.
     
    #10 galaxee, Apr 12, 2007
  11. dogfriend

    dogfriend Human - Animal Hybrid

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    <div class='quotetop'>QUOTE(galaxee @ Mar 25 2007, 07:02 PM) [snapback]412096[/snapback]</div>
    Hi Galaxee

    I have two questions:

    1. How often are you expected to use the parking brake? I live and work (park) on flat ground, so I tend not to ever use the e-brake. Do you need to use once a week, once a month, or other?

    2. How much clearance should there be between the shoe and drum when doing a manual adjustment?

    Thanks in Advance
     
    #11 dogfriend, Apr 13, 2007
  12. galaxee

    galaxee mostly benevolent

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    #12 galaxee, Apr 14, 2007
  13. dogfriend

    dogfriend Human - Animal Hybrid

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    <div class='quotetop'>QUOTE(galaxee @ Apr 13 2007, 09:47 PM) [snapback]423141[/snapback]</div>
    Thanks for the reply. :)
     
    #13 dogfriend, Apr 14, 2007
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