Topic: Pitted disc break piston

[Popwood]

Hi, All, it's been a long time since I posted.

I'm servicing the disc break caliper on '75 CB550. I've found the chrome has some pitting on the piston. It's located exactly where the rubber seal lives in its groove. There are traces of the High Vac grease that got past the seal. Not much grease but I'm sure none is what's best.

How much of a problem could this be? Any fixes to suggest? Some years ago I had front forks leaking a bit of oil on my CB750. I discovered some chrome pitting just above the seal. I got "creative" and thoroughly cleaned the area then filled pits with JB Weld. Then I wet sanded the filler flush to the metal with 600 grit wet/dry abrasive. Any thoughts on that approach?

Thanks for any thoughts, suggestions.

[jlh3rd]

random thoughts.......get another piston, why worry .........brake pistons have to deal with heat/cooling cycles, JB weld is excellent but i'd wonder how it holds up to this...........or, what have you got to lose, except maybe you're brake failing when you need it.......a fork tube is a little different.
.....probably wouldn't fail catastrophically, just start leaking......get a new piston...

[Popwood]

I take your point, thanks. I suppose a NOS piston would not present a fitment problem. 

[jlh3rd]

i thought you were talking nos.....

[754]

You can get stainless  pistons out of Germany for 50 bux or less shipped, the guy sells Allen bolt kits too like around 22 bux..

[bryanj]

Same piston on CB 360 twin, 350 four, 400 four, 500twin, 500 four, 550 four and look at it this was you only got one neck!
Also fit new seal and clean the groove out with something like a dental pick as a dremel brush just polishes the crud

[Popwood]

Thanks, All,
Just ordered new piston from David Silver Spares. Cylinder all cleaned up, especially the groove for the seal. I also have a dental mirror so I can inspect the groove.

[754]

 Your Whizzer, is it an H model or a J model ? And what frame is it in ?

[Jerry Rxman Griffin aka MuthaF'er]

Welcome back 

[my name is nobody]

a little late, but ebay seller had them in stainless for about 37.00 last time I bought one. 

[rotortiller]

Some guys use these. http://power-barn.com/honda-replacement-phenolic-front-brake-caliper-pistons-for-cb350-cb360-cb400-cb450-cb500-cb550-cb750-45107-323-020/ I have used the replacement steel ones from https://4into1.com/front-brake-caliper-piston-45107-392-003-honda-cb750/ and unfortunately it is slightly smaller by a few thousands of an inch  causing poor retraction by the rubber seal, it works and it does not leak but it will drag the pads more. I'd measure the old and new before installation.

[my name is nobody]

a little late, but ebay seller had them in stainless for about 37.00 last time I bought one. 

Forgot to mention sellers store name is "dgs38" if anyone is interested..

[Popwood]

754, The Whizzer was on a Schwinn bicycle frame, the kind with a front fork spring. Don't know the model number. Here's a nice little story behind it:

Grew up in a small town. There was a tradition that each year a high school senior would gift the bike to a junior. I was the lucky one. Then the following year I passed it on. I did get pulled over by a cop while riding it without a helmet. Really? I argued before the judge it wasn't really a motorcycle and therefore not subject to mandatory helmet law. Judge wasn't hearing any of that.