brake pistons

[N0tac0p]

has anyone considered making phenolic (or other durable material) brake pistons?  the OEM steel ones are exposed and rust and lock up and........

i would think many riders would be interested in these as their replacecments.  thoughts?

[Skinhead]

Probably couldn't handle the heat.

[hubcapsc]

I take my calipers apart whenever I change pads... keeps them working good,
and keeps the piston-crud out of the insides... 



I was intimidated at first, but there's nothing in a caliper... the caliper body,
the pistons and a couple of seals...

-Mike

[N0tac0p]

its the outside thats the problem it is raw steel and at the wheel  gets it wet, dirt, etc and it rust.  PS autmobiles have compsite pistons they handle the heat?

[hubcapsc]

its the outside thats the problem it is raw steel and at the wheel  gets it wet, dirt, etc and it rust.  PS autmobiles have compsite pistons they handle the heat?

When people put new pads on without addressing what you're talking about, the outside
goes inside.

If our pistons never had to be pushed in, crud on the outside of the pistons would be
just a cosmetic issue...

Our metal (chromed?) pistons are pretty studly, and they clean up real good.

phenolic composites - has been of especial interest recently due to mass savings and possible reduction in brake corner judder sensitivity to disc thickness variation.

                                               http://papers.sae.org/2013-01-2050/

Sounds like they have advantages... if our bikes had them, they'd still get gunked up on the outside...
I wonder if plastic pistons would  still be "within specs" after I got done running 1200 grit sandpaper on them
to clean them? 

-Mike

[Ricky-D]

Although I've never had one apart, I'm not so sure the pistons are steel.

Have you taken a magnet to see if they actually are steel?

***

[N0tac0p]

i'll do that right after work as i will be rebuilding them

[tank_post142]

i have a couple of spares stuck to a magnet on my outside fridge. a good cleanup and they can be used probably forever.

[da prez]

  Some of the bigger trucks I worked on had phenolic pistons. I have seen them as large as 2 1/2 inches. I have cleaned them up and reused them. There is a lot more heat generated on those 16 in disc brakes than on our bikes. I have not looked , but with the size , they could probably be found. 

                                     da prez

[xman]

Hey Mike, if you don't mind can you explain your procedure. How you get them out, cleaning, seals and assembly. I'm going to do mine for the first time soon.

Tom

[John Schmidt]

Hey Mike, if you don't mind can you explain your procedure. How you get them out, cleaning, seals and assembly. I'm going to do mine for the first time soon.

Tom

Easy, remove the caliper from its mounting position and squeeze the brake handle(or foot pedal). Before doing that, take one pad out, squeeze until both pistons pop out and are pressing against the pad. Remove the pad and put a spatula in its place and squeeze the handle(or foot pedal) some more until the pistons come all the way out. The spatula will prevent them from flying out, but allows them to come out just far enough to clear their housing. Best to have a bucket under the caliper 'cuz it gets messy. When doing the front brakes, all four pistons won't come out at the same time. So leave the pad in place on the one that both pistons are extended and continue to squeeze the handle until all four are out. Then put the spatula in...might need to do one caliper at a time at this point.

I used to have a 1" piece of bar stock with an old Wing brake m/c and a piece of brake hose attached mounted on the bar stock and in a vise. I would remove the caliper and attach the odd hose to it on my bench, then holding it over a bucket would squeeze the handle to pump the pistons out using hydraulic pressure. So, go pick up a spare m/c off any bike at a junk yard, get an old handlbar and cut it down so you can mount it in a vise, scrounge a 20" piece of brake line and you can do it in just a few seconds every time.

[hubcapsc]

Hey Mike, if you don't mind can you explain your procedure. How you get them out, cleaning, seals and assembly. I'm going to do mine for the first time soon.

Tom

Once you get the calipers off (brake fluid eats paint and all that) and drained as best
you can, you need to get the pistons out. I use compressed air, and safety glasses. A
thin board (some use a paint stick) keeps the pistons from flying out like bullets, and
also, if one piston came out and the other didn't all the air would just come out the
empty hole leaving the other piston stuck in there... This shows two 1bys with the
pistons blown out a little, you can see that contamination of the piston goes
beyond just what is normally exposed.



Take out one of the boards and blow them out further, and then they pretty
much can just be pulled out. I use an old air gun attachment of my father's,
similar to this to blow the pistons out:



Sometimes it is hard to get the little caps that cover the pins off, and the pins themselves
are stuck sometimes. I use as big a flat head screwdriver as possible on the caps and a
good allen wrench to get the pins out. Do it some way where you have good leverage,
don't strip out the screwdriver slot on the cap or the allen head on the pin... I like
to do it like this:



When you put the cap and pin back, anti-seize is your friend, and it won't
be a problem the next time. The first time I did one, I boogered up the cap
head, and then boogered up the caliper trying to drill it out, you can generally
find another caliper on eBay for $35 or so 

You might think the rear wheel has to come off, but not really. Some people take the
caliper off the bracket. I just get started on my normal wheel-off procedure and
stop when the axle is out far enough to remove the caliper...



Get the caliper and pistons clean with 1000 or 1200 wet-dry sandpaper (or
something, I use the sandpaper). Nitrile gloves are good while you're cleaning,
I use brake fluid as the wet for my sandpaper. The bores where the pistons go
need to be clean, as well as the grooves where the seals go. I get the
grooves as clean as I can, without ever managing to get them perfect,
and it seems to be "good enough"... perfect would be better 



That's a "speed bleeder" in the above picture, replaces the normal bleed valve
and makes bleeding and easy one man job. Here's a speed bleeder write-up
on shoptalk...

http://www.valkyrieriders.com/ShopTalk/speedbleeders.htm

Make sure the pins are lubed, we have floating calipers. Don't lube the
pins that the pads ride on, or your pads  ... but do clean the contamination
off the pins that your pads ride on, new pads will ride at a different (and
dirty) place than the old pads were at.

-Mike

[sandy]

An old trick we use on boat trailers with surge brakes. When you rebuild the wheel cylinders, put some waterproof grease under the rubber dust boot. This kept the water out of the piston and prevented rust. Would it be possible to coat the piston outside of the seal with Bel Ray. This would stop the gunk and rust from building up.

[N0tac0p]

putting sticky grease or anything on the outside will HOLD contaminants and may stop the piston from releasing and therefore cause premature pad wear.  folks rebuilding brakes don't even put lube where teh pads slide for fear of crap getting caught and stopping them from moving properly

[old2soon]

When I rebuilt my rear caliper for cleaning the bores on the caliper and cleaning the pistons I used Scotch Brite. The one I used IS NOT metal-Nylon I believe but that could be wrong. AND when I got done with the clean up the bores and the pistons looked like new.  RIDE SAFE.