Brake Pistons - Replace or Reuse?

Smudgemo

Smudgemo

Intermodal Man of Mystery
Joined
May 17, 2019
Messages
573
Location
Berkeley, CA
Bike
'08 GS / '78 CB550
The title pretty much sums it up. I can sorta feel some of the corrosion with my fingernail, but not really with my fingers. I scrubbed them with a blue scotchbrite type of kitchen sponge to get them to this point, and I kinda sorta think they're fine, but being that they are front brakes and not something less critical, I figured I'd see if anyone has an informed opinion. They were not leaking when I took things apart, but they weren't really retracting and it made for a noticeable drag trying to move the bike around. I noticed one piston on each side moved more willingly than the other, but I'm guessing that's by design. All were removed without a piston wrench or visegrips (master cylinder and compressed air) and the brake fluid looked fine. I can buy new pistons, but don't want to if not necessary.

Note that this bike is a project that I've never ridden, so I can't say anything more about the present situation of the brakes. The rear seems to work properly, though..

Pistons.jpg

Thoughts?
 
You could clean these up some more with some emery paper and see how they look. I think they are marginal now. You also need to remove the seals and clean the grooves the seals fit into. The gunk behind the seals builds up and can cause the pistons to drag as the seals are pushed into the pistons and they bind.
 
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Cleaning the groove behind the seals is a must. Dental pick and a wire wheel on a dremel tool until they are spotless. Make your dental hygenist proud. And if you're re-using the seals, be sure to scrape off any crud with your fingernails. Current pistons are marginal. Make a judgement call.
 
I haven't had a chance to remove the seals yet, but I'm ordering parts tonight and wanted to solicit opinions on pistons in case they aren't considered in bad shape. Marginal on brakes means I buy new ones. Thanks for the input.
 
If the pistons are not retracting, new seals would be in order especially if all other cleaning has been done.
Fresh rubber will hold on to the piston, flexing, then pull the piston in ever so slightly/very importantly.
 
Smudgemo said:
I haven't had a chance to remove the seals yet, but I'm ordering parts tonight and wanted to solicit opinions on pistons in case they aren't considered in bad shape. Marginal on brakes means I buy new ones. Thanks for the input.
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With brakes always replace if there is any doubt at all. Life is to short….
 
If the corrosion goes in past the seals replace them. If it doesn't it shouldn't hurt to use them.
 
My limited experience with calipers has been if the pistons are showing corrosion, the calipers are worse. I'd take a very close look at the bores.
 
When I did mine, there was corrosion in the O-ring groove of the calipers. Not bad, but there. The calipers are aluminum so go easy with cleaning the groove, bore, etc. As long as it cleans up and the pitting is minor the calipers will probably be OK. I have a tool made from an old spade drill bit that has been ground down to an edge and bent over 90* with heat. It worked perfectly to gently scrape the O-ring grooves clean. The key here is gently. The solution to preventing future corrosion is more frequent fluid changes.

Moving on to the pistons. Those would be marginal to me. If I had to, I'd run them, but plan on replacing them soon in the next season. The gripe I had with Honda is these are steel pistons with a plated coating. If there is corrosion pitting now, its already through the coating, and will only continue after you have cleaned them up with scotchbrite, emery, etc. Coating them with Castrol red grease will help slow the problem, but it's still there. The solution is new Honda pistons. These too will degrade over time, but probably not in the lifetime of the bike given its already 20+years old.

I also really like the aftermarket stainless steel pistons https://www.ebay.com/itm/3234130237...:Honda&hash=item4b4ceb1c11:g:wfIAAOSw899bgJ6L These seem to be a good solution, provided the quality is there. I rebuilt my front calipers a little over a year ago. Had pitted pistons similar to yours, slightly bigger pits, but fewer of them. At the time I could only get two pistons, so I cleaned up the best two and reinstalled. They have been fine. Its hyperbole to imply the brakes will fail due to this minor pitting. I plan on rebuilding all the calipers over next winter as by then I'm sure I'll need brake pads, and they will be getting stainless pistons installed.

RT
 
As above, the pistons are marginal, but can be cleaned up with emery paper. Partsfish has them for $30 each, the ebay stainless kit is $67 for 2 pistons + the seals, much better deal if the quality is there.

Aside from semi annual brake fluid changes I got into the habit of pulling the wheels in March and mid season to clean the pads, lube the sliding pins and clean the pistons. Leave the pads in on one side and use a small piece of 1/4" plywood to fill in for the disk remove pads, pump out the pistons 3/4 out and then clean them thoroughly using a strip of rag and some brake fluid. Lube them lightly and then use a C clamp to push them in and do the other side. This kept everything working the way is was supposed and minimise any ongoing corrosion issues.
 
I never understood why motorcycle brake caliper dust seals aren't designed to move in and out with the pistons as they do on automotive brake pistons. This design minimizes the amount of the piston that is exposed to the outside elements to only the part outside of the dust seal. Since this exposed part never comes in to contact with the hydraulic seal anyway, it doesn't matter if it has some damage from being exposed. Anyone have any idea why they don't use the same design idea? Is it simply to make the calipers as compact as possible?
 
Andrew Shadow said:
I never understood why motorcycle brake caliper dust seals aren't designed to move in and out with the pistons as they do on automotive brake pistons. This design minimizes the amount of the piston that is exposed to the outside elements to only the part outside of the dust seal. Since this exposed part never comes in to contact with the hydraulic seal anyway, it doesn't matter if it has some damage from being exposed. Anyone have any idea why they don't use the same design idea? Is it simply to make the calipers as compact as possible?
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I've often wondered the same... why don't motorcycle brakes have dust seals around each piston? As you mentioned Andrew, maybe it's a space issue... it is pretty tight between pistons.
 
Andrew Shadow said:
I never understood why motorcycle brake caliper dust seals aren't designed to move in and out with the pistons as they do on automotive brake pistons. This design minimizes the amount of the piston that is exposed to the outside elements to only the part outside of the dust seal. Since this exposed part never comes in to contact with the hydraulic seal anyway, it doesn't matter if it has some damage from being exposed. Anyone have any idea why they don't use the same design idea? Is it simply to make the calipers as compact as possible?
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If I had to hazard a guess it would be space constraints. Motorcycles don't have what I'd consider to be a dust seal. To me, a dust seal is like an automotive style expanding boot/bellows that completely protects the pistons. Another reason why I wonder about the logic of Honda, or Nissen for that matter exposing the plated steel to the elements. Seems like not a good idea.

RT
 
I just ordered new pistons from Honda at $22 per, seals, dust seals, etc. I've been busy rebuilding the carbs so I haven't tried to remove the seals from the calipers yet, but so far they look okay.
 
pmatulew said:
Cleaning the groove behind the seals is a must. Dental pick and a wire wheel on a dremel tool until they are spotless. Make your dental hygenist proud. And if you're re-using the seals, be sure to scrape off any crud with your fingernails. Current pistons are marginal. Make a judgement call.
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Fully agree with the first bit. Personally, I wouldn't put anything metal or abrasive into the bore of my brake calipers. I use plastic toothpics, cocktail sticks, old tooth brushes and clean brake fluid. And compressed air.
 
+1 to jfheath’s post above. Anything above aluminum on the Mohs scale and the odds of a scratch causing a leak aren’t worth it in my mind.

My personal best friends for cleaning the groove are Dollar Store tooth picks soaked in brake fluid.
 
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