TeGGer® wrote:
> "Caroline" > sprach im
> . net:
>
>
>
>>Brake pistons do freeze in their cylinders, though. I completely
>>disassembled my front brakes this past summer. As you can imagine, it
>>doesn't take but a little rust buildup on the piston/cylinder walls to
>>impede operation.
>
>
>
>
> I find it's more often gum than rust that sticks up the pistons. Rust tends
> to invade from the outside, weather being the source. Rust sticks at first,
> but rapidly becomes a fluid leak.

if the seal is running on a corroded surface. where you have a steel
piston & an aluminum cylinder [like the master cylinder assembly], the
seal is static on the steel, and slides on the non-corroding alloy
surface. in this situation, there is little or no wear acceleration
above what would happen normally. the exception is where corrosion is
chronic on a system that has not moved /and/ has badly contaminated
[wet] brake fluid. then you get electrolytic reactions between the
steel piston & alloy cylinder & severe pitting, but even then, due to
cunning design, the main compression seals are ahead of the pitting area
as the pistons are behind them. the exception is the wiper seal at the
rear, and if that leaks, it's a pita, but it's not as serious as a main
compression seals.

for front [honda] slave cylinders, you have a very hard smooth well
sealing surface for the seals to slide on, the chrome. as long as the
chrome remains intact, again, wear is insignificant. chromed pistons
can corrode, but that is lessened considerably by regularly changing
brake fluid and doing the silicone trick you describe below.

>
> Honda, unlike Toyota, uses non-stainless steel pistons. Toyota's are
> stainless.

the stainless/non-stainless argument has factors in favor for each.
stainless can still corrode. depends on environment & grade. most
stainless still pits badly in salt. honda [nissin, etc.] pistons are
chrome plated forged steel. this is a very high quality base
material/fabrication route. chrome plating is also many times more wear
resistant than most stainless steels. there's also the potential for a
fatigue advantage - stainless has no fatigue endurance limit, a lot of
non-stainless [ferritic] steels do. finally, the smooth surface of the
chrome is pretty much as good as it gets for fluid seal quality & long
life - as long as it remains intact.

as above, the single easiest way to prevent corrosion on a chrome steel
piston is to make sure the brake fluid is changed regularly.

> Wish Honda would do that too. With Toyota you just clean the gum
> off and put it back. With Honda you end up replacing the piston, and it's
> not cheap.
>
> One problem with reman calipers is that nobody seems to use silicone grease
> on the piston and seals when putting it all back together. They all use
> brake fluid as a lubricant because it's cheaper. Silicone grease helps
> prevent the buildup of gum and keeps the pistons moving freely for much
> longer. Brake fluid dries out and BECOMES gum.

the silicone grease is very important. but brake fluid is cited for the
inner seals because it contains rubber preservatives. left to its own
devices, the rubber would become hard & crack over time. my personal
view is to lightly silicone lube the piston on assembly, then ensure the
boot has sufficient silicone to make the seals air/water tight from the
outside.

>
> If the caliper is not yet installed, you can just pop the piston out of the
> new calipers with some air pressure (even with a bicycle pump with some
> electrical tape wrapped around the end to seal it), smear it with some
> silicone and reinstall. Observe surgical cleanliness here, by the way,
> that's crucial.
>
> If it's already installed, it's a bit more complex:
>
> You can get around this with the judicious use of a syringe from a
> woodworking supply store <http://tinyurl.com/6z9j2>, and some silicone
> grease.
> http://www.tegger.com/hondafaq/rustybrakes/syringe.jpg
>
> What you do is to have a helper step on the pedal as necessary to push the
> piston out of its bore most of the way, so the dust boot is mostly
> extended. One full pedal push will move the piston about 1/16".
>
> NOTE: ONLY do this if you've been regularly using the pedal-push method of
> brake bleeding, or put a block of wood under the pedal so it can't go any
> farther than what it does in normal driving!

don't agree about the block - see above. both you & curly regularly
repeat that advice. i don't doubt the sincerity of your intent, but
it's bad advice in any situation requiring brake bleeding. i can see
that it's possible to get away with it on hondas because they bleed
quite easily, but other vehicles can be sob's and the /only/ way to
bleed them reliably is to use full pedal travel to expell all air.
otherwise the air simply compresses & expands within the cylinder again
the moment the pedal is released. if the cylinder is corroded enough
for this to be a concern in the first place - it should be replaced
anyway. pitting can be a fatigue nucleator. i've never seen it happen,
but theoretically, a cylinder could burst if a fatigue crack propagated.

i appreciate the concern about scoring seals & causing leaks, and on low
grade detroit iron, that has some validity, but in high quality honda
systems, corrosion sufficient to be a concern is rare. any
"coincidence" about leakage following any brake bleed proceedure is much
more likely to be caused by fresh brake fluid interacting with
contaminated old seals.

>
> Use Brakleen or other aerosol brake cleaning solvent to remove the dirt
> from the piston and boot first.
>
> Then you ease the syringe under the boot and inject silicone as close to
> the hydraulic seal as possible all around the perimeter of the piston. Turn
> the piston with a set of channel-locks so you can more easily apply
> silicone to the portion that was closest to the top of the caliper. Now
> push the piston back in all the way with a C-clamp. Pedal-pump it back out
> again and repeat a few times.

much better to disassemble and clean the whole workings. all pressing
the piston back in does is ensure the goop gets forced up past the seals
contaminating the fluid & getting stuck in the cylinder/piston gap where
it can cause wear & further corrosion.

/if/ pushing the piston back, it's also prudent to open the bleed nipple
first. avoids pushing contaminated fluid back up into the master cylinder.

>
> When you're done, if the siliconing has been done properly, you should see
> the piston move out with a pedal push, but then move back IN again slightly
> when the pedal is released.
>
> The grease is just silicone dielectric grease. I use Zip-Slip just because
> for me it was easy to get. http://www.themoldersedge.com/polish.htm
>
> Here's another example:
> http://www.mgchemicals.com/products/8462.html

thanks for the links! like your applicator!

>
> Googling for
> silicone dielectric grease
> turns up many more.
>
>