Author Topic: Front Brake Caliper Piston (Read 1700 times)

The Sovereign Man · « **on:** August 21, 2020, 10:57:44 PM »

What’s everyone’s thoughts on these pistons?

Piston #1

Piston #2

Usable? I see people replacing them when they’re pitted. Not sure how it affects operation.

RAFster122s · « **Reply #1 on:** August 21, 2020, 10:59:29 PM »

I wouldn't try to use them. Not worth the risk in my book.

spotty · « **Reply #2 on:** August 21, 2020, 11:37:42 PM »

my thoughts would be that #1 is fcuked, the pitting is on the end that goes where the seal is and would probably either leak, chew out the seal or just plain not work

#2 has the damage at the other end which pretty much just sits inside the caliper and goes nowhere near the seal so could be ok, having said that it still has to go through the seal to get inside the caliper and so could damage the seal on the way through

on the other hand $22 for new piston and seal...
https://www.ebay.com/itm/Brake-Caliper-Piston-Kit-CB450K-70-71-CB750K-69-76/324031648793?fits=Model%3ACB750&hash=item4b71ca9419:g:owgAAOSwOUNe2a8b

The Sovereign Man · « **Reply #3 on:** August 22, 2020, 12:10:15 AM »

Quote from: spotty on August 21, 2020, 11:37:42 PM

my thoughts would be that #1 is fcuked, the pitting is on the end that goes where the seal is and would probably either leak, chew out the seal or just plain not work

#2 has the damage at the other end which pretty much just sits inside the caliper and goes nowhere near the seal so could be ok, having said that it still has to go through the seal to get inside the caliper and so could damage the seal on the way through

on the other hand $22 for new piston and seal...
https://www.ebay.com/itm/Brake-Caliper-Piston-Kit-CB450K-70-71-CB750K-69-76/324031648793?fits=Model%3ACB750&hash=item4b71ca9419:g:owgAAOSwOUNe2a8b

Unfortunately, at least in regards to motorcycle parts, I’m in Australia. Trying to avoid lengthy, and expensive, shipping if I can help it.

spotty · « **Reply #4 on:** August 22, 2020, 02:35:34 AM »

i'm here too ( cold and wet melbourne, we had snow and hail today...)

might still be worth giving your local honda dealer a yell on monday, at least see what they're asking for the part

the othger thing is that one fom china might actually get sent via real post rather than the snail mail they use when its free post, they estimate 12+ days, at the moment free post is somewhere around 2 months ( where are my chainsaw parts you bastards ?)

if you do end up ordering one from O/S its probably worth paying a bit more and getting a stainless one, never have this problem again

Little_Phil · « **Reply #5 on:** August 22, 2020, 03:25:55 AM »

https://www.ebay.co.uk/itm/74-76-HONDA-CB550K-CB550F-FRONT-BRAKE-CALIPER-PISTON-W-SEAL-CI-CBFCPS-A/254338058256?hash=item3b37bac810:g:IAQAAOSwQTVV9nTA

DaveBarbier · « **Reply #6 on:** August 22, 2020, 04:16:30 AM »

Yeah, one with the pitting around the seal area is toast. The other one is probably ok, just use brake fluid or brake fluid compatible assembly lube when installing so it slides in easily. I would go with stainless or phenolic personally so you won’t have to worry about corrosion anymore.

Or if you have access to a lathe, make your own.

disco · « **Reply #7 on:** August 22, 2020, 04:43:46 AM »

https://www.cruzinimage.net/2018/05/17/69-76-honda-cb750k-front-brake-caliper-piston-w-seal/

Not worth the hassle. I’m Australia too. Order from Cruizin Image. Usually you’ll have the item within a week.

Bodi · « **Reply #8 on:** August 22, 2020, 04:53:05 AM »

I went with phenolic about 5 years ago and have no complaints. I think it is a Ford brake piston with some modification done by the seller. Regardless the original hardchromed ones last decades so whatever you can get quickly is probably best. The one pitted at the seal is unusable, IMO the other can be used in a pinch... likely from a caliper removed and then stored a long time in a humid place.

bryanj · « **Reply #9 on:** August 22, 2020, 08:02:34 AM »

Wouldnt use either, you only got one neck!
I use stainless but UK post aint too bad

754 · « **Reply #10 on:** August 22, 2020, 08:07:45 AM »

Polish the pitted areas down on 2 , so it does not harm seal... don't matter if it gets under size there.

bryanj · « **Reply #11 on:** August 22, 2020, 12:11:59 PM »

You gotta get one so get two, why risk it iffy brakes just aint worth it, i had an 18 wheeler fail, luckily not at full 90000 lb but you discover adrenalin is funny and brown!!!

DaveBarbier · « **Reply #12 on:** August 22, 2020, 04:09:17 PM »

If there’s no pitting under where the seal goes there’s zero problem running that piston.

BenelliSEI · « **Reply #13 on:** August 22, 2020, 04:56:17 PM »

I try and always do the complete job, and you won’t ever have to do it again...... replace both.

bryanj · « **Reply #14 on:** August 23, 2020, 12:21:13 AM »

There IS a problem as you have to get the damaged area through the tight seal, sorry I WILL NOT AND CAN NOT UNDERSTAND penny pinching on such a critical area as brakes, if you dont care about your life fine but what about the person you hit when they fail

DaveBarbier · « **Reply #15 on:** August 23, 2020, 04:20:09 AM »

Jeepers creepers, fine replace the piston. All you squares care about life so much, if it makes you happy replace it

If it was me alone in my shop I’d smooth out the pits so it won’t hurt the seal going in and I wouldn’t give it another thought because it will function 100% as a new piston would. But if you all were here throwing a tantrum I’d give in just to shut you up, haha

The Sovereign Man · « **Reply #16 on:** August 23, 2020, 05:48:40 PM »

I don’t understand how pitting, which is recessed not raised, will affect either the seal or the operation?

Genuinely trying to understand the mechanics of it here, not trying to be a smart arse.

I get it if there’s corrosion etc. that is raised on the surface. But if the surface is otherwise smooth and the imperfections are recessed, what is that going to do?

ekpent · « **Reply #17 on:** August 23, 2020, 06:00:14 PM »

If the recess is inline with the rubber seal there is a possibility that there could be a brake fluid leak under the seal through that recess. I have re-used pistons before with some slight pitting especially if I replace worn out brake pads and the seal rides in a better section of the piston. New is always good but these are so easy to tear down that a leaker can be addressed easily if indeed new parts are needed.
Some people have filled minor pits with JB Weld and smoothed out, not sure if Super Glue could hold up to brake fluid. The chances of an instant catastrophic complete front brake failure is pretty minimal as long as there is fluid in the master but pads and discs can get compromised reducing braking power.

spotty · « **Reply #18 on:** August 23, 2020, 06:02:34 PM »

The seal, which basically operates under pressure, will expand into the gap made by the pitting and get cut up by the rough edges
Also , even if the pitting were as smooth as the dimples on a golf ball, brake fluid will fill the pits and once past the seal will leak that fluid into the big wide world, or in this case onto the brake pad
Also also, once the pitting has emptied itself of fluid into your brake pads it will then carry air back past the seal into the caliper and make the brakes spongy

The number 2 piston from your original pics shouldn't do any of these things as the pitting is way below the working area that the seal contacts. If you wish to give it a good polish and ease it gently through the seal it should've ok
But.....to get either of those pistons out of a caliper will have involved dragging that pitting through the seal which will therefore have damaged them and they'll leak anyway.so minimum you're needing a new seal even if you want to use number two piston

seanbarney41 · « **Reply #19 on:** August 23, 2020, 06:58:58 PM »

Quote from: The Sovereign Man on August 23, 2020, 05:48:40 PM

I don’t understand how pitting, which is recessed not raised, will affect either the seal or the operation?

Genuinely trying to understand the mechanics of it here, not trying to be a smart arse.

I get it if there’s corrosion etc. that is raised on the surface. But if the surface is otherwise smooth and the imperfections are recessed, what is that going to do?

you are probably exactly right. In fact, I would bet $100 that you can slam that junk together and it will work fine for many years. But, no one wants to be that guy that told you it will be ok when your brakes fail and you slam into the back of minivan at 65 mph. Get it? You have already figured it out for yourself. So stop asking questions on the internet that you know you are going to disregard and take responsibility for your own actions.

low-side · « **Reply #20 on:** August 23, 2020, 07:26:56 PM »

I've never had a pitted caliper piston leak (I'm sure it could though), but pitting can cause problems. If the pitting is in line with the seal, the seal doesn't flex the way that it should and the piston doesn't retract properly, causing dragging brakes. Piston #1 is definitely in that camp. #2 has pitting that isn't in line with the seal, so it would probably be fine. Personally, I'd order new for both while it's apart.

The Sovereign Man · « **Reply #21 on:** August 23, 2020, 08:03:01 PM »

Thanks for the input everyone

To be clear, I’ll order new parts when I have a shopping list to minimise the shipping costs. In the meantime I’ll reuse the best-of-a-bad-bunch caliper piston (I actually found a third ... also pitted haha) and the seal that looks visibly okay.

News:

Author Topic: Front Brake Caliper Piston (Read 1700 times)

The Sovereign Man

The Sovereign Man

The Sovereign Man

The Sovereign Man