Topic: Is my brake caliper piston toast?

[csendker]

Just got it out and cleaned up (used the grease gun, what a cleanup job...).  Unfortunately, it looks pitted; is this toast or can it be revitalized somehow?  If it's toast, where do you get replacements?  I've looked briefly, but only found the rebuild kits.

[csendker]

...while the caliper itself seems to be cleaning up nicely.  No pitting or other nastys in here to report.  The seal popped out with no problem, still pliable (but not to be reused).  There was brake fluid charged in it when I acquired the assemblt (I got everything from the handle/master cylinder on down).

[Bob Wessner]

Is my brake caliper piston toast?

I'm afraid so. Check out the parts FAQ for sources, they are available.

[mrbreeze]

I paid a pretty penny for one from the dealership but have seen them on ebay that are way cheaper.One guy had some that were special made out of a different metal that wouldn't corrode like the stock gem.

[csendker]

I found one at Old Bike Barn, but is seems to be hollow, while mine is solid???  Maybe this is one thing I should pop the $$ for at the dealer, it's always nice to be able to stop.

[csendker]

That must be some expensive filling in the piston.  The hollow one from OBB is $23.95.  Service Honda has (presumably) the real deal for $63.60.  Yeesh.  I'll have to call tomorrow to see what the local shop has to offer.

[Jughead]

Send me an Email with the Measurements and a Picture of the Pad Side I think I may have a GoodUsed one.

[TwoTired]

I believe your caliper piston is usable.  Replace if you wish.  But, I have used ones that were worse without incident and they functioned properly without leaks.
What are the drawbacks?
Stopping won't be a problem.  However, if the pitting aligns with the seal, puck retraction will be slow and extra drag may result.  Severe cases heat the disc rotor.

I'd try it.  If it drags beyond your desires, then replace it.  Lately, I've even been reusing the rubber seal if feels pliable and resilient and isn't deformed.

My opinion/experience.

[oldbiker]

There is a guy who regularly sells caliper pistons on eBay made from a phenolic material. I havn't used one but I've read sevaral complimentary reports. They are quite cheap too.

[mutters]

Is the 'solid' piston really filled in ??
My old k1 piston has a cap over the end, for no apparent reason,but as it has a twin brake conversion I can't guarrantee it's not off an earlier model.
Your piston may be the same

[Raul CB750K1]

You can tray the phosphoric acid with the rust; it will eat up the rust and leave a smooth surface if the metal has not been eaten up; or maybe a very soft wire wool or sandpaper. I would also give it a try, but won't risk with the seal; it's only a couple of bucks original Honda part.

Raul

[TwoTired]

The original piston is chrome plated.  Not certain what phosphoric acid will do to the chrome.  But, removing the chrome or making it less slippery doesn't strike me as a good idea.

Cleaning the pits doesn't seem productive.  And deepening them with acid is counter productive. I use brake assembly fluid to arrest the rust process, or at least delay the onset.  I do try and keep the pit edges smoothed/ rounded with emery cloth.

If you don't feel qualified to assess the seal condition, then replace it.  I allways used to replace it until I had the new one next to an old one and if they looked and felt the same, I began to question why replacement was needed.  Though some of the old ones were clearly distorted.  I've only reused a couple of them.  But, they are still working fine.

Cheers,

[Bob Wessner]

Seems to me there just some things you don't take chances with, tires, chains/sprockets and brakes. There's a lot riding on them, pun intended.

[csendker]

I probably could reuse this one, but considering the whole reason I'm rebuilding this is because my existing brakes drag somewhat, I'd rather try to upgrade to a better piston to minimize the potential of slow/bad retraction.  I was just surprised to see the replacement one pictured hollow when mine is capped/filled with something.  And even more surprised with the price spread between aftermarket & Honda. 

I looked for the ebay guy, but couldn't find anything.  I'm going to mic my existing one, and if Jughead has a good used one, I'd rather upgrade.  Or, I'll consider getting an aftermarket piston unless someone can convince me a hollow one is a bad thing.  Mine definitely is capped, and seems to be filled (heavy).  The picture of it sitting on my computer clearly shows the cap-thing.  Who knows, this may be an aftermarket piston and it should have been hollow all along.  What are they normally?

And I'm definitely going with a new seal.  I agree with Bob on this one, and would rather not take chances until I'm much, much more familiar with the potential consequences.  Epically on the brakes.  Of course, that doesn't mean I'm throwing this one away.

[Terry in Australia]

Good point Bob. I'd replace it, there was a guy on Ebay selling stainless steel pistons that will not be affected by rust or knackered brake fluid like the OEM chrome plated steel items.

I've got some Brembo twin opposed piston calipers that I bought for my racer, and was surprised to see that they have alloy pistons, albeit anodised, with a special coating added to make them less likely to be damaged by the afore-mentioned nasties. A lot bloody cheaper than the Honda items too, at $25.00 US per PAIR!

Oh, by the way, your piston/s aren't solid, they have a cap with a slight "dome" which allows the pad to "pivot", so as to maintain flush contact with the disc and wear evenly. Cheers, Terry.

[Bob Wessner]

csendker,

I'm assuming we're talking about a 750K1? If so, I checked my parts list that covers the 750, 750K1 and 750K2. All use the same piston (part#), hollow with a metal cap. My K0 piston is like this.

Maybe that additional mass in your filled piston is adversely affecting how it withdraws?? Don't know, just a thought.

[csendker]

550 K1

[Bob Wessner]

Oops, sorry, can't speak to that then. 

[csendker]

Mind you, this is out of the spare caliper I bought, not my bike.  So if the 'additional mass' does adversely affect piston retraction, it was for someone else.  Anyone with a 550 out there know if they're like the one I have (capped, presumably filled)?  Or can get (hollow & open)?

[bryanj]

500(twin and four)/550/400/250 (never seen in US)/360 All used the same piston WWW.davidsilverspares.co.uk did have stock at, i think £25 + shipping. You can use one of the Wing ones, its fractionally shorter and has a groove at the end for the dust seal that you dont use--works perfect in mine I did have some kits which cost me £17.50 and included the seal if you want me to look PM me

[csendker]

I found the SS piston ebay guy:

http://cgi.ebay.com/ebaymotors/Honda-CB750-K-CB-750-450-CB450-new-brake-caliper-piston_W0QQitemZ4603928161QQcategoryZ35592QQrdZ1QQcmdZViewItem

Looks like 750 only, no 550's.  I'm going to measure mine tonight (after getting some calipers on the way home) and weigh my options.

DSS does have them:
     CB550K3 : Brake caliper piston  ....  £22.00
     CB550K3 : Brake caliper piston oil seal  ....  £1.95

[bryanj]

As I remember it the only difference 750 to 550 piston is length so why not ask that ebay seller if he will do you a shorter one

[TwoTired]

The pictures of your caliper pistons look just like the one in my stock Cb550s.

[csendker]

38 mm diameter & 34 mm tall.  No dome on the 'capped' end.

[Terry in Australia]

50 bucks? Geez, time to fire up the lathe!