brake shoes

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Old 10 Sep 2006, 09:27 pm   #1 (permalink)
camry-keeper
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Default brake shoes

Brake shoes, what a design - an engineer run amok. Can see why disc brakes
are more common on the rear in finer cars. The drum rusts to the hub
plate, the painstaking star wheel adjuster mechanism and parking brake
cable connection, the wacky hold down spring and c-crimp washers, let's
count all the varieties of springs, squeaky friction points, measure the
diameter of the drum to tenths of a mm-with what? who thought this stuff
up? Ok, so they wear practically forever and aren't nearly as dusty, I'll
give 'em that much, but no more.

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Old 10 Sep 2006, 10:38 pm   #2 (permalink)
edokamoto@netzero.net
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Default Re: brake shoes

Drum brakes have a self energizing system. So if you pull the
emergency brake lever to force the shoe against the drum it will wedge
tighter to the drum as the drum tries to rotate. That is why alot of
mercedes or other cars have a little drum brake built inside the rear
disc brake. My instructor at Pasadena City College said one time a
fire truck disc emergency brake failed and the unoccupied fire truck
rolled down those steep San Francisco streets, awful.
Of course if you don't pull the emergency brakes hard enough it
won't wedge properly. But disc emergency brakes must always maintain
sufficient squezzing pressure.
camry-keeper wrote:
> Brake shoes, what a design - an engineer run amok. Can see why disc brakes
> are more common on the rear in finer cars. The drum rusts to the hub
> plate, the painstaking star wheel adjuster mechanism and parking brake
> cable connection, the wacky hold down spring and c-crimp washers, let's
> count all the varieties of springs, squeaky friction points, measure the
> diameter of the drum to tenths of a mm-with what? who thought this stuff
> up? Ok, so they wear practically forever and aren't nearly as dusty, I'll
> give 'em that much, but no more.


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Old 11 Sep 2006, 09:00 am   #3 (permalink)
Daniel
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Default Re: brake shoes

camry-keeper wrote:
> Brake shoes, what a design - an engineer run amok. Can see why disc brakes
> are more common on the rear in finer cars.


Let's try an attitude adjustment.
Drum brakes on the Toyota are designed like everything else on the car
- thoughtfully.

The drum rusts to the hub
> plate,


Knowing this, spray some penetrating oil around the center prior to
removal. Use 8mm x 1.25 bolts in the threaded holes provided,
progressively tightening alternatively to remove the hub - same process
as removing the front rotors. I found the bolts at the local hardware
store for $1.60 each.

the painstaking star wheel adjuster mechanism

Just be careful. You remove one spring and one clip and the adjusting
level fits over the rear brake shoe.

and parking brake
> cable connection,


Just pull back the long spring covering the parking brake cable and
hold the cable with pliers to reveal the cable end. If you unhook the
spring from the automatic adjustment lever first, it will swing out of
the way and you simply unhook the parking brake cable from the end of
the rear brake shoe.

the wacky hold down spring and c-crimp washers,

All drum brakes have the same kind of hold down springs. There's a
special tool that all the auto parts have for removing them in about
two seconds. For installing them back, I found it easier to just push
in and then turn the top washer with my thumb and finger.

let's
> count all the varieties of springs,


Brake shoe return spring (goes in those "C" shaped cutouts in the
shoes. Use vice grip pliers and pushing in on the last shoe when
hooking it into position), anchor spring (couldn't be much simpler -
just hook one end to the hole at the bottom of each brake shoe), hold
down springs (also easy to install - skip tool and use hand pressure,
springs are light weight) auto adjust lever spring - just examine it
very carefully to see the way it hooks together before disassembly. The
end at the lever goes over, the other end goes under, and it goes in
the hole directly in line with the other end.


squeaky friction points,

That's where you apply the brake grease. Not too difficult or much
different than taking apart and lubricating the slide pins on the disk
calipers.

measure the
> diameter of the drum to tenths of a mm-with what?


You're supposed to use a vernier caliper. Auto parts stores sell
digital versions these days for under $20. You could also just check
the depth of wear at the ridge between the worn and adjacent portion of
the drum. Read the spec. for the difference between new and maximum
wear, and you can see the amount of wear permitted. I found minimal
wear, would guesstimate .001 -.002" well within limits. If the shoes
were worn down to the backing plate, I'd just replace the drums, or you
could carry them into a shop to be machined, but then I replace the
rotors also. The idea of brake systems is to dissipate heat, so I
prefer to have more metal, not less.

who thought this stuff
> up?


Ever see the big wooden lever on a stage coach or buckboard wagon in
old Westerns - that's the genesis of the idea. Drum brakes are
practically as old as automobiles. Large trucks still use them.
Properly maintained, the only real advantage of disk brakes is that
they dry quicker if you've gone through a deep puddle, and if you're
doing a lot of braking, they cool faster.

Ok, so they wear practically forever and aren't nearly as dusty, I'll
> give 'em that much, but no more.


Because they wear practically forever, you might do them once during
your ownership of the car. Just do it right, take your time, the basic
principle is very simple. If you don't like doing brake work, just take
them to a shop - they all do brakes. My problem is I don't trust shops
to do anything on the car. Brake work is often something the
inexperienced mechanics are given to learn, whereas if you have the
service manual, and go carefully, you can wind up with a better job.

I have it kind of backwards. When I took Auto Shop in High School we
only worked on drum brakes, so it is disk brakes that were new to me.
They're both the same principle - converting the energy of motion into
"kinetic atomic motion" in the cast iron disk, drum, and surrounding
air, which "energy has spread out (in a diffused and non-directional
form) to occupy all of the possible states of a system which can store
it." So the 3,000 pound vehicle moving at sixty miles per hour,
converts its energy into altering the vibrational states of the
molecules in the iron.

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Old 11 Sep 2006, 10:18 am   #4 (permalink)
Daniel
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Default Re: brake shoes

camry-keeper wrote:
> the painstaking star wheel adjuster mechanism

=============
Ever look at it closely?
The teeth are actually curved, like the escapement mechanism in a
mechanical clock.
If the thread pitch is 1mm - apx. .040", and there are twenty teeth,
turning one tooth would move the end apx. .002"
Now if there were no self adjustment mechanism and it was necessary to
manually adjust the brake shoes every time they wore .002", and you had
to turn the adjuster tight into the drum and then back it off one
tooth, I might agree with you that the drum brakes are an annoying
anachronism, but actually they take care of themselves for 150,000 -
200,000 miles or more.

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Old 11 Sep 2006, 11:55 am   #5 (permalink)
johngdole@hotmail.com
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Default Re: brake shoes

All these parts will still be cheaper than a disc brake with an
integrated cable-actuated emergency brake. And yes, the self-servo
effect makes it ideal in emergency systems. But cost is still a major
consideration. Today, drum rear brakes are available as the system of
choice on, uhhh...low end cars.

Disc brakes were patented in 1901 by a British inventor Frederick
William Lanchester. But the disc system's efficiency is mostly not
needed and the higher pedal force needed to operate them was only
overcome in 1964 with the introduction of Studebaker's power boost
system.



camry-keeper wrote:
> Brake shoes, what a design - an engineer run amok. Can see why disc brakes
> are more common on the rear in finer cars. The drum rusts to the hub
> plate, the painstaking star wheel adjuster mechanism and parking brake
> cable connection, the wacky hold down spring and c-crimp washers, let's
> count all the varieties of springs, squeaky friction points, measure the
> diameter of the drum to tenths of a mm-with what? who thought this stuff
> up? Ok, so they wear practically forever and aren't nearly as dusty, I'll
> give 'em that much, but no more.


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