rear brakes maladjustment

yups · 03-20-2007, 03:12 PM

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.

brick · 03-20-2007, 06:44 PM

<div class='quotetop'>QUOTE(yups @ Mar 20 2007, 04:12 PM) [snapback]409138[/snapback]</div>

Quote:

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.
[/b]

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.

yups · 03-20-2007, 09:14 PM

<div class='quotetop'>QUOTE(brick @ Mar 20 2007, 06:44 PM) [snapback]409246[/snapback]</div>

Quote:

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.
[/b]

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.

tochatihu · 03-21-2007, 09:15 AM

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.

brick · 03-21-2007, 03:16 PM

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.

yups · 03-21-2007, 10:44 PM

<div class='quotetop'>QUOTE(tochatihu @ Mar 21 2007, 09:15 AM) [snapback]409493[/snapback]</div>

Quote:

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.
[/b]

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.

tochatihu · 03-22-2007, 09:58 AM

<div class='quotetop'>QUOTE(yups @ Mar 21 2007, 07:44 PM) [snapback]409949[/snapback]</div>

Quote:

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.
[/b]

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.

galaxee · 03-25-2007, 10:02 PM

the prius' brake system self-adjusts using the parking brake. unfortunately, said "self adjustment" isn't always enough. periodic manual adjustments may be needed.

yups · 03-27-2007, 05:38 PM

<div class='quotetop'>QUOTE(galaxee @ Mar 25 2007, 10:02 PM) [snapback]412096[/snapback]</div>

Quote:

the prius' brake system self-adjusts using the parking brake. unfortunately, said "self adjustment" isn't always enough. periodic manual adjustments may be needed.
[/b]

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

galaxee · 04-12-2007, 08:02 PM

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.

03-21-2007, 09:15 AM	#4
tochatihu Senior Member Join Date: Apr 2004 Location: Kunming Yunnan China Posts: 1,823 My Car: 2001 Prius Package: Pioneer #1 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 7	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. __________________ DAS Tochatihu, the Hopi hummingbird kachina

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03-20-2007, 03:12 PM	#1
yups Join Date: Aug 2006 Posts: 36 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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.

03-21-2007, 03:16 PM	#5
brick Senior Member Join Date: Dec 2006 Location: Columbia, SC Posts: 700 My Car: 2007 Prius Package: #2 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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.

03-25-2007, 10:02 PM	#8
galaxee running WOT until out of fuel Join Date: Mar 2005 Location: central NC/ western WI Posts: 9,080 My Car: 2005 Prius Package: #5 Nominated 5 Times in 3 Posts TOTM Awards: 0 Friends: 21	the prius' brake system self-adjusts using the parking brake. unfortunately, said "self adjustment" isn't always enough. periodic manual adjustments may be needed.

04-12-2007, 08:02 PM	#10
galaxee running WOT until out of fuel Join Date: Mar 2005 Location: central NC/ western WI Posts: 9,080 My Car: 2005 Prius Package: #5 Nominated 5 Times in 3 Posts TOTM Awards: 0 Friends: 21	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.