Can anyone check whether brake pistons move freely?

How does a DIY check that brake caliper & pistons move freely.

In a related thread on how to diagnose high speed braking induced wheel
shimmy in a 98 Toyota 4Runner and in a variety of brake shimmy articles it
was suggested I check that the 4 pistons move freely in each caliper.

.... (eg [url]http://www.eurac-group.com/technote4.htm[/url]
[url]http://journals.pepublishing.com/index/77665U68739575J1.pdf[/url]
[url]http://www.babcox.com/editorial/bf/bf100326.htm[/url]
[url]http://www.estech.co.jp/list.pdf/%20customer/cust41.pdf[/url] etc) ...

Unfortunately, neither the $20 Chilton nor the $200 Toyota Repair Manuals I
bought say ANYTHING about how to check the pistons & calipers for free
movement.

Each caliper has 4 pistons (which the Toyota shop manual says to separate
with a MONKEY WRENCH!).

Do you know how to check that the caliper & 4 pistons move freely?

"Stuart A. Bronstein" <spamtrap@lexregia.com> wrote in message
news:4tGOf.56515$dW3.49182@newssvr21.news.prodigy.com...[color=blue]
> How does a DIY check that brake caliper & pistons move freely.
>
> In a related thread on how to diagnose high speed braking induced wheel
> shimmy in a 98 Toyota 4Runner and in a variety of brake shimmy articles it
> was suggested I check that the 4 pistons move freely in each caliper.
>
> ... (eg [url]http://www.eurac-group.com/technote4.htm[/url]
> [url]http://journals.pepublishing.com/index/77665U68739575J1.pdf[/url]
> [url]http://www.babcox.com/editorial/bf/bf100326.htm[/url]
> [url]http://www.estech.co.jp/list.pdf/%20customer/cust41.pdf[/url] etc) ...
>
> Unfortunately, neither the $20 Chilton nor the $200 Toyota Repair Manuals
> I
> bought say ANYTHING about how to check the pistons & calipers for free
> movement.
>
> Each caliper has 4 pistons (which the Toyota shop manual says to separate
> with a MONKEY WRENCH!).
>
> Do you know how to check that the caliper & 4 pistons move freely?[/color]

Yep.
Remove pads, and check that all four pistons require a similar amount of
force to push back in.
If they're seized for any reason, it'll be pretty obvious.

By Shimmy I take it you mean a vibration?
In that case it's most likely to be unevenly worn discs, or something not
running true.
Only way to check that is by using a dial gauge and checking disc run-out.


*** Free account sponsored by SecureIX.com ***
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"Stuart A. Bronstein" <spamtrap@lexregia.com> wrote in message
news:4tGOf.56515$dW3.49182@newssvr21.news.prodigy.com...[color=blue]
> How does a DIY check that brake caliper & pistons move freely.
>
> In a related thread on how to diagnose high speed braking induced wheel
> shimmy in a 98 Toyota 4Runner and in a variety of brake shimmy articles it
> was suggested I check that the 4 pistons move freely in each caliper.
>
> ... (eg [url]http://www.eurac-group.com/technote4.htm[/url]
> [url]http://journals.pepublishing.com/index/77665U68739575J1.pdf[/url]
> [url]http://www.babcox.com/editorial/bf/bf100326.htm[/url]
> [url]http://www.estech.co.jp/list.pdf/%20customer/cust41.pdf[/url] etc) ...
>
> Unfortunately, neither the $20 Chilton nor the $200 Toyota Repair Manuals
> I
> bought say ANYTHING about how to check the pistons & calipers for free
> movement.
>
> Each caliper has 4 pistons (which the Toyota shop manual says to separate
> with a MONKEY WRENCH!).
>
> Do you know how to check that the caliper & 4 pistons move freely?[/color]

remove the brake pads and refit the caliper, it should now be possible to
slide the caliper (if it is a sliding caliper) using hand pressure.

usually 4 piston calipers are not sliding type.

with the pistons pushed out a bit (by carefully pressing the brake pedal) it
should be possible with strong hand pressure to push each and every piston
back in to the caliper.
A short lever may be used if you are weak or it is difficult to get a
purchase. It is usually easy to tell if any piston is sticking, it will be
obvious by the greater amount of pressure needed.

while the pistons are sticking out a bit you can check for rust or damage to
the polished outside surface of the piston.

brake shudder is almost invariably caused by warped discs


mrcheerful

"M Cuthill" <moray_dot_cuthill@v21.me.uk> wrote in
news:440b3e48$0$14378$6d36acad@titian.nntpserver.com:[color=blue][color=green]
>> Do you know how to check that the caliper & 4 pistons move freely?.[/color]
> Remove pads, and check that all four pistons require a similar amount
> of force to push back in.[/color]

Do they make a brake piston force guage which works on 4 piston calipers?

I just realized that replacing the rotor and pads will not solve my brake
vibration problem if the pistons are sticking!

To answer your question, I tried pushing the eight front pistons in with a
disc brake spreader. The knob twisting seemed the same for both sides of
each caliper - but I don't have a force guage in my hand to measure it!
[color=blue]
> By Shimmy I take it you mean a vibration?
> Only way to check that is by using a dial gauge and checking disc
> run-out.[/color]

The runout, even after indexing and cleaning of the hub mating surfaces, is
within spec (0.0028 inches), yet there is still horrible brake judder upon
high-speed (over 50 mph) braking.

I'm beginning to realize replacing the rotors and pads won't solve the
long-term problem if the true cause is the pistons sticking causing pad
material to be deposited unevelnly on the rotors.

Here's what StopTech has to say about the true cause of brake shudder:
"Every case of "warped brake disc" that I have investigated ... has turned
out to be friction pad material transferred unevenly to the surface of the
disc [resulting] in thickness variation (TV) ... due to hot spotting that
occurred at elevated temperatures."
[url]http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml[/url]

So, now it's time to diagnose the brake pistion force "Despite the popular
myth, brake judder is not caused by warped rotors. Judder is the result of
a thickness variation in pad buildup on the rotors' surfaces" due to
pistons sticking [url]http://www.zeckhausen.com/avoiding_brake_judder.htm[/url]

So, I think we finally found the answer as to the main cause of brake
shimmy! Replacing the rotors and pads will not solve the problem long term.

Is there a brake piston force guage that I can buy on the Internet?
Stu

If you have more than 75k miles on them just replace them. You could just
pull them off and have someone hit the brakes and watch them close.

On Sun, 05 Mar 2006 19:55:02 -0000, Stuart A. Bronstein
<spamtrap@lexregia.com> wrote:
[color=blue]
> "M Cuthill" <moray_dot_cuthill@v21.me.uk> wrote in
> news:440b3e48$0$14378$6d36acad@titian.nntpserver.com:[color=green][color=darkred]
>>> Do you know how to check that the caliper & 4 pistons move freely?.[/color]
>> Remove pads, and check that all four pistons require a similar amount
>> of force to push back in.[/color]
>
> Do they make a brake piston force guage which works on 4 piston calipers?
>
> I just realized that replacing the rotor and pads will not solve my brake
> vibration problem if the pistons are sticking!
>
> To answer your question, I tried pushing the eight front pistons in with
> a
> disc brake spreader. The knob twisting seemed the same for both sides of
> each caliper - but I don't have a force guage in my hand to measure it!
>[color=green]
>> By Shimmy I take it you mean a vibration?
>> Only way to check that is by using a dial gauge and checking disc
>> run-out.[/color]
>
> The runout, even after indexing and cleaning of the hub mating surfaces,
> is
> within spec (0.0028 inches), yet there is still horrible brake judder
> upon
> high-speed (over 50 mph) braking.
>
> I'm beginning to realize replacing the rotors and pads won't solve the
> long-term problem if the true cause is the pistons sticking causing pad
> material to be deposited unevelnly on the rotors.
>
> Here's what StopTech has to say about the true cause of brake shudder:
> "Every case of "warped brake disc" that I have investigated ... has
> turned
> out to be friction pad material transferred unevenly to the surface of
> the
> disc [resulting] in thickness variation (TV) ... due to hot spotting that
> occurred at elevated temperatures."
> [url]http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml[/url]
>
> So, now it's time to diagnose the brake pistion force "Despite the
> popular
> myth, brake judder is not caused by warped rotors. Judder is the result
> of
> a thickness variation in pad buildup on the rotors' surfaces" due to
> pistons sticking [url]http://www.zeckhausen.com/avoiding_brake_judder.htm[/url]
>
> So, I think we finally found the answer as to the main cause of brake
> shimmy! Replacing the rotors and pads will not solve the problem long
> term.
>
> Is there a brake piston force guage that I can buy on the Internet?
> Stu[/color]


You'll see that though. & it's a race car issue, not a road car one. Most
raod car judder seems to be soft suspension bushes exagerating small
amounts of warp.

"Stuart A. Bronstein" <spamtrap@lexregia.com> wrote in message
news:qmHOf.65951$PL5.40749@newssvr11.news.prodigy.com...[color=blue]
> "M Cuthill" <moray_dot_cuthill@v21.me.uk> wrote in
> news:440b3e48$0$14378$6d36acad@titian.nntpserver.com:[color=green][color=darkred]
>>> Do you know how to check that the caliper & 4 pistons move freely?.[/color]
>> Remove pads, and check that all four pistons require a similar amount
>> of force to push back in.[/color]
>
> Do they make a brake piston force guage which works on 4 piston calipers?
>
> I just realized that replacing the rotor and pads will not solve my brake
> vibration problem if the pistons are sticking!
>
> To answer your question, I tried pushing the eight front pistons in with a
> disc brake spreader. The knob twisting seemed the same for both sides of
> each caliper - but I don't have a force guage in my hand to measure it!
>[color=green]
>> By Shimmy I take it you mean a vibration?
>> Only way to check that is by using a dial gauge and checking disc
>> run-out.[/color]
>
> The runout, even after indexing and cleaning of the hub mating surfaces,
> is
> within spec (0.0028 inches), yet there is still horrible brake judder upon
> high-speed (over 50 mph) braking.
>
> I'm beginning to realize replacing the rotors and pads won't solve the
> long-term problem if the true cause is the pistons sticking causing pad
> material to be deposited unevelnly on the rotors.
>
> Here's what StopTech has to say about the true cause of brake shudder:
> "Every case of "warped brake disc" that I have investigated ... has turned
> out to be friction pad material transferred unevenly to the surface of the
> disc [resulting] in thickness variation (TV) ... due to hot spotting that
> occurred at elevated temperatures."
> [url]http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml[/url]
>
> So, now it's time to diagnose the brake pistion force "Despite the popular
> myth, brake judder is not caused by warped rotors. Judder is the result
> of
> a thickness variation in pad buildup on the rotors' surfaces" due to
> pistons sticking [url]http://www.zeckhausen.com/avoiding_brake_judder.htm[/url]
>
> So, I think we finally found the answer as to the main cause of brake
> shimmy! Replacing the rotors and pads will not solve the problem long
> term.
>
> Is there a brake piston force guage that I can buy on the Internet?
> Stu[/color]

the easiest way for you to satisfy yourself as to the ease of piston
movement is to strip the caliper completely, with no piston seals at all the
cleaned pistons should be able to fall freely in and out of the caliper.

the initial problem is usually a heavily worn disc or a disc that has excess
runout, this leads to disc thickness variations which is what most people
call warped discs.

replace the discs, check that they do not have excess runout, and that the
pistons move freely and that the pads are not tight in their locations, all
will now be fine.


mrcheerful

mrcheerful<nbkm57@hotmail.com> wrote in
news:8QHOf.30836$wl.17519@text.news.blueyonder.co.uk:[color=blue][color=green]
>> I just realized that replacing the rotor and pads will not solve my
>> brake vibration problem if the pistons are sticking!
>> Do they make a brake piston force guage which works on 4 piston
>> calipers?[/color]
> Use your hands.
> With the pistons pushed out a bit (by carefully pressing
> the brake pedal) it should be possible with strong hand
> pressure to push each piston back in to the caliper[/color]
[color=blue]
> the easiest way for you to satisfy yourself as to the ease of piston
> movement is to strip the caliper completely, with no piston seals at
> all the cleaned pistons should be able to fall freely in and out of
> the caliper.[/color]

Hi Mr Cheerful,

Thanks for the advice. I guess I just assumed there was a tool to measure
brake piston sticking. If there isn't a tool, I can do what you say and
test it by hand with the calipers disassembled.

Luckily these 1998 Toyota 4Runner front calipers are the easiest I've seen
in my life to work on. We don't even need to remove a single bolt to get
the brake pads out. All we do is remove a clip by hand, then pull two pins
by hand, pop out the anti-vibration spring by hand, and then pull out the
two brake pads and two anti-squeal shims per pad.

Looking in my Toyota Repair Manual, I can see that it only takes two bolts
to remove the calipers from the car (in addition to the brake line).

Then it says to pry out the four "cylinder boot set rings and boots" per
caliper, which at first I presumed was the same as the "piston seals" you
speak of. But, reading on, Toyota says to blow out the pistons with
compressed air (placing a wood plate in the space where the rotor was).

Only then, the repair manual says to pry up the four "piston seals" with a
quarter inch flathead scewdriver. The Toyota Repair Manual exploded diagram
shows four "set rings", "boots", "pistons", and "piston seals", in that
order, outward from the rotor in both directions.

The problem then becomes, how does one test piston force after removing the
piston seal when the pistons are already out of the calipers by this time.

Still, there's no harm in taking the calipers apart.
The shop manual says to lubricate some areas with "lithium soap base glycol
grease" and others with "disc brake grease". Aren't they the same thing?

So many questions ... so much to learn!
Stu

Stuart A. Bronstein wrote:
[color=blue]
> How does a DIY check that brake caliper & pistons move freely.[/color]


It's easy. Remove calipers from their mount brackets and support them
so the flex hose is not strained. Have helper step on brake pedal and
observe distance the piston(s) moves out. Both pistons on both sides
ought to be the same. And, ideally, they should retract ever so
slightly once the pedal is raised back up again.

Unless the pads are worn to a skin, don't worry about the pistons being
accidentally ejected in your test. It will take a number of pedal
presses before that even remotely becomes a danger.

"Stuart A. Bronstein" <spamtrap@lexregia.com> wrote in message
news:Y7MOf.44920$H71.10895@newssvr13.news.prodigy.com...[color=blue]
> Hi Mr Cheerful,
>
> Thanks for the advice. I guess I just assumed there was a tool to measure
> brake piston sticking. If there isn't a tool, I can do what you say and
> test it by hand with the calipers disassembled.
>
> Luckily these 1998 Toyota 4Runner front calipers are the easiest I've seen
> in my life to work on. We don't even need to remove a single bolt to get
> the brake pads out. All we do is remove a clip by hand, then pull two pins
> by hand, pop out the anti-vibration spring by hand, and then pull out the
> two brake pads and two anti-squeal shims per pad.
>
> Looking in my Toyota Repair Manual, I can see that it only takes two bolts
> to remove the calipers from the car (in addition to the brake line).
>
> Then it says to pry out the four "cylinder boot set rings and boots" per
> caliper, which at first I presumed was the same as the "piston seals" you
> speak of. But, reading on, Toyota says to blow out the pistons with
> compressed air (placing a wood plate in the space where the rotor was).
>
> Only then, the repair manual says to pry up the four "piston seals" with a
> quarter inch flathead scewdriver. The Toyota Repair Manual exploded
> diagram
> shows four "set rings", "boots", "pistons", and "piston seals", in that
> order, outward from the rotor in both directions.
>
> The problem then becomes, how does one test piston force after removing
> the
> piston seal when the pistons are already out of the calipers by this time.
>
> Still, there's no harm in taking the calipers apart.
> The shop manual says to lubricate some areas with "lithium soap base
> glycol
> grease" and others with "disc brake grease". Aren't they the same thing?[/color]

Just to break in, in case you're just about to do the job ;)

Mr Cheerful's method doesn't involve any dissasembly of the caliper for the
test he describes.

--

Tony Bond / UncleFista

[url]www.bradford7.co.uk[/url]

Love is like a snowmobile, speeding across the frozen tundra.
Which suddenly flips, pinning you underneath.
At night the ice-weasels come...

Stuart A. Bronstein wrote:[color=blue]
> ...The shop manual says to lubricate some areas with "lithium soap
> base glycol grease" and others with "disc brake grease". Aren't they
> the same thing?[/color]



This is not answering your question directly. However, from the discussion
in the link, it is clear that whatever you pick, don't choose any grease
that contains petroleum products.

"Why you should never use Copper grease anywhere near your brakes"
[url]http://www.bikersoracle.com/vfr/forum/showthread.php?t=44119&page=3&pp=15[/url]

--
Lin Chung
[Replace "the Water Margin" with "ntlworld" for e-mail].

Oops....
[url]http://www.bikersoracle.com/vfr/forum/showthread.php?t=44119&page=1&pp=15[/url]

--
Lin Chung
[Replace "the Water Margin" with "ntlworld" for e-mail].

In article <Y7MOf.44920$H71.10895@newssvr13.news.prodigy.com>,
Stuart A. Bronstein <spamtrap@lexregia.com> wrote:[color=blue]
> Then it says to pry out the four "cylinder boot set rings and boots" per
> caliper, which at first I presumed was the same as the "piston seals"
> you speak of. But, reading on, Toyota says to blow out the pistons with
> compressed air (placing a wood plate in the space where the rotor was).[/color]

I did my SD1 Rover front calipers recently and these have 4 pistons each.
After removing from the car, use a bleed nipple(s) from the other side to
seal the pipe(s) inlet. Get a rubber tyre valve - the type used in
tubeless tyre wheels, remove the valve core, and fit it to a tyre
compressor or foot pump. Secure all the pistons using G Clamps - etc. Push
the tyre valve onto a bleed nipple which is open and apply air pressure
and release a G Clamp gradually till one pops out. Be careful as fluid
will go everywhere and there is considerable force around. Once you've
discovered how far they have to go to come out you can adjust the other G
Clamps to stop them only just in time. You then put the one that's come
out back in just enough to make a seal.

Examine the pistons and bores for damage or corrosion after a thorough
clean. Damaged piston replacements can usually be bought separately.
[color=blue]
> Only then, the repair manual says to pry up the four "piston seals" with
> a quarter inch flathead scewdriver. The Toyota Repair Manual exploded
> diagram shows four "set rings", "boots", "pistons", and "piston seals",
> in that order, outward from the rotor in both directions.[/color]
[color=blue]
> The problem then becomes, how does one test piston force after removing
> the piston seal when the pistons are already out of the calipers by
> this time.[/color]
[color=blue]
> Still, there's no harm in taking the calipers apart. The shop manual
> says to lubricate some areas with "lithium soap base glycol grease" and
> others with "disc brake grease". Aren't they the same thing?[/color]

What you want is red rubber grease. Most decent accessory shops should
have it.
[color=blue]
> So many questions ... so much to learn![/color]

--
*I love cats...they taste just like chicken.

Dave Plowman [email]dave@davenoise.co.uk[/email] London SW
To e-mail, change noise into sound.

"Stuart A. Bronstein" <spamtrap@lexregia.com> wrote in message
news:Y7MOf.44920$H71.10895@newssvr13.news.prodigy.com...[color=blue]
> mrcheerful<nbkm57@hotmail.com> wrote in
> news:8QHOf.30836$wl.17519@text.news.blueyonder.co.uk:[color=green][color=darkred]
> >> I just realized that replacing the rotor and pads will not solve my
> >> brake vibration problem if the pistons are sticking!
> >> Do they make a brake piston force guage which works on 4 piston
> >> calipers?[/color]
> > Use your hands.
> > With the pistons pushed out a bit (by carefully pressing
> > the brake pedal) it should be possible with strong hand
> > pressure to push each piston back in to the caliper[/color]
>[color=green]
> > the easiest way for you to satisfy yourself as to the ease of piston
> > movement is to strip the caliper completely, with no piston seals at
> > all the cleaned pistons should be able to fall freely in and out of
> > the caliper.[/color]
>
> Hi Mr Cheerful,
>
> Thanks for the advice. I guess I just assumed there was a tool to measure
> brake piston sticking. If there isn't a tool, I can do what you say and
> test it by hand with the calipers disassembled.[/color]

Personally I wouldn't bother checking the caliper pistons, as IME the
chances of sticky pistons causing judder or shimmy is remote. The most
likely cause is distortion or chilling of the disc. Chilling can cause hard
spots on the swept surface of the disc. The uneven friction can cause judder
of the brakes.
The only cure in either case is to fit new discs, which is what I would do
If I had the same problem.
Mike.

>or chilling of the disc. Chilling can cause hard[color=blue]
> spots on the swept surface of the disc. The uneven friction can cause
> judder
> of the brakes.[/color]

Care to explain what "chilling" is?