pistons froze in caliper

[yamtom]

Ive started to work on my MNS, and want to clean out the front brakes since the brakes are spongy. Ive got one caliper off, and the piston doesnt want to move. Ive put the air to it, and there is too much leakage to make it come out. I have read here, that pounding on the piston, from a large dowel with a hammer, while the caliper rests against a piece of wood, will push the piston in, and then maybe air pressure might work. This seems kind of rough, but if the caliper can take it, I will try it. What say you?

[Tarheeltriple]

YanTom, reatach the caliber to the brake line leaving it hang beside the wheel, put a drip pan under it and maybe some rags to catch the fluid, then level the handlebars so the brake res is level, remove the cover, always checking to ensure the brake res does not go dry, use the brake handle to pump the cylinder out of the caliber.

[Bergman16]

I used the grease gun method on all three of my stuck and rusty pistons. Worked perfectly, just a bit of grease to clean up but not a big problem at all. They just ease right out.

[Bonz]

When you say air leakage, are you talking around the pistons themselves? That would mean the seals are dry? I gather there is a good seal so air isn't coming out elsewhere?

But if not dry, try pounding the piston in with a dowel and it won't be too rough. If there is a crusty ring of gunk that should break it free and then try air again. If the piston gets a "running" start with air pressure, should make it come out like you need. Obviously make sure to put a rag in the caliper for the piston the hit, other wise it is an amazing sound and fury when a piston comes out unabated with air behind it. Keep fingers ABSOLUTELY out of the way, it will hurt, break or mangle them when the piston comes out. Let the rag be your catchers mitt.

Last month I upgraded the ZRX1200 stock calipers to GSXR front calipers (from eBay, messy and gunked up inside is an understatement) and air was the way I freed them when rebuilding. Make sure bleeder screw is closed and you get a good seal to the hole the banjo screws into (where you inject the air) and I've not seen a caliper piston able to withstand a good shot of air.

[yamtom]

ok bonz and others

I was trying to shoot air into the bleeder hole, I was losing the air , no seal. Will try all if needed. Thanks

[MPittma100]

Caliper Pistons

When you do get the pistons out, they will most likely need to be replaced. Almost everyone I have rebuilt needed a new piston. They pit near the seal and dust boot causing a fluid leak. As was previously mentioned, be VERY aware of the force that the piston has behind it when it finally exits the caliper. It WILL hurt you.

Aftermarket stainless steel pistons are available from several sources. Search the site for them.

[Tarheeltriple]

Try the grease gun method 1st sense you have the caliper off already.
Plug/seal the hole in caliper where the brake line attached, then loosen the bleeder valve and connect the grease gun directly to the bleeder valve it will click right on then then pump the grease gun forcing the piston out.

[bikerphil]

If you fill the caliper with brake fluid before using the grease gun, it will be a lot less messy and you will use not as much grease.

[yamtom]

ok,, I got them out

Keep in mind this bike has only twenty k miles on it. The brakes on the front were very weak when I bought the bike, and I never rebuilt them. Not sure if I even bled them though I must have four yrs ago before I went on hiatus.

Both the calipers and the pistons are pristine after wiping them off, I pushed them out with the brake fluid, and blocking the line with clamp. There is just a bit of that famous brown gunk at the back of the bore of the caliper, everything cleaned up fine cleaned up fine. There is just a bit of rust on the pistons at the very edge of the piston, I think that is ok, but I will clean it off anyway. These pistons are marked SS, so I assume that means they are stainless steel.

Everything looks really good, I will clean them up further, does anyone think there is any use to using the finest of the 3 M stuff to further polish them. Also, I assume that the seal absolutely must come out, but is this true with stuff as pristine as these are? The seals look fine, not a ragged edge at all and absolutely no rust or that white crud anywhere near them. The pistons do go in and out fairly easily by hand, but only up to the point of hitting against the seals.

[3Phase]

Tom,

If they're SS pistons they're expensive. Just clean them off and don't try to polish them, it can mess up the surface.

Yes, you have to take the seals out of the calipers and carefully clean the groove.

Clean the cylinder bores in the calipers too but don't go crazy. The pistons do have to fit the bores but the actual seal is made with the rubber and the piston.

Be nice to those pistons!

.

[yamtom]

caliper bores are spotless,

The caliper bores are spotless. There is some minor rust on the pistons, to the pad side of the groove. I will clean the rust off minimally, clean the o ring surface off minimally to get it spotless, put em back together and hopefully be in business. I am assuming that it is not critical to change the o rings for new ones, correct?

[3Phase]

Oh, man, you're asking about something that no one except you can see and feel.

The seals could be totally worthless even as scrap rubber or they might be alright if they're relatively new and they haven't been... gnawed upon.[1]

If you remember how they came out then you can clean 'em off, flip 'em around and use the second lip while you save up for a full set of front and rear brake kits.

If the seals aren't good it won't matter how you put them in or how much lube you use, the pistons will stick and they won't retract when you release the brake. Nothing will immediately explode but they'll eventually eat up the brake pads, cook off the brake fluid and generally make it difficult to stop.


So, do you think the seals are still good enough to use?



1.) Antonio Banderas as Ahmad ibn Fadlān ibn al-Abbās ibn Rāšid ibn Hammād (aka "Ibn"), "The 13th Warrior."

.

[bikerphil]

There should be no need for new caliper seals in most cases, it is crucial to remove them and clean the crud out from behind them, otherwise you will have sticking calipers.

[yamtom]

two entirely different responses, haha

I love this place. Well saving up is not necessary, I will call my local dealer tomorrow and see what they have in stock, probly nothing. I was thinking in terms of actually getting it on the road quick is all. Is georgefix the go to guy for this stuff too.?? I will do the cleaning and only if they look perfect will I attempt to re use them. I suspect, by the time I am done digging them out, they may not be looking so good. Thanks

[trbig]

As Phil mentioned.. Use a pick or something to remove the square O-ring, then use something to clean all the corrosion that is on the back side of that groove the O-ring sits in. Corrosion expands behind the seal and pushes the O-ring against the piston, causing hanging brakes. Then use a rag soaked in brake fluid and wipe the seal down really well, looking for any pits or scarring. If they're still smooth, I'd just re-use them.