Author Topic: Is my caliper piston useable???? (Read 4418 times)

1975cb550 · « **on:** March 12, 2008, 01:31:48 PM »

my caliper was frozen and then i got the piston out with a lil work. but it's somewhat pitted i don't know if it's still useable. here is a pic. its not to good quality but maybe it'll help.

TwoTired · « **Reply #1 on:** March 12, 2008, 01:41:33 PM »

I'm not sure. But, if you make the picture fuzzier, I'd say yes for sure.

Nice focus in the box of Kleenex though...

mystic_1 · « **Reply #2 on:** March 12, 2008, 01:43:29 PM »

most digital cameras have a "macro" mode, it's icon is often a flower, that lets you take extreme close-ups with good focus. Perhaps your camera has this feature?

mystic_1

fonz · « **Reply #3 on:** March 12, 2008, 02:48:33 PM »

Where exactly is it pitted? If it's on the inside of the piston, or on the end, I'd say it's alright, provided it's not pitted to the point of almost being eaten through. If the pitting is on the sides, I wouldn't use it, as the sealing ability would be compromised.

number13 · « **Reply #4 on:** March 12, 2008, 03:04:25 PM »

I recently tried re-using a piston that looked
very similar, it was not useable and had to be replaced.

1975cb550 · « **Reply #5 on:** March 12, 2008, 03:12:48 PM »

i think its the finish that screws the camera up. i'm not sure though. i think this pic is better

fonz · « **Reply #6 on:** March 12, 2008, 03:19:11 PM »

Personally, I wouldn't put much effort into that piston.

1975cb550 · « **Reply #7 on:** March 12, 2008, 03:31:20 PM »

where can i get a new piston? and how much am i looking at?

fmctm1sw · « **Reply #8 on:** March 12, 2008, 03:37:19 PM »

I bought one of those phenolic pistons from a guy here. Worked in my 350F...

fonz · « **Reply #9 on:** March 12, 2008, 03:38:24 PM »

Does bikebandit.com have them?

TwoTired · « **Reply #10 on:** March 12, 2008, 05:05:02 PM »

If money is tight, you can probably re-use that piston. It won't leak, but there is some risk that the caliper seal won't retract it properly, and allow the fiction elements to drag.

PM Kevin Hunter ( Kevin400F ) He sold me phenolic pistons that I intend to use on the next brake rebuild.

Cheers,

Blueridgerunner · « **Reply #11 on:** March 12, 2008, 06:02:17 PM »

the last time I checked the phenolic pistons were available on eBay. Won't fit my 650 tho. Had to get mine from David Silver Spares in the UK

hymodyne · « **Reply #12 on:** March 12, 2008, 06:09:47 PM »

I had a reused pitted piston ruin a trip to lake champlain. the last 150 miles of the trip, I my front caliper rubbed and built up heat... a new piston is well worth the money.

hym

UnCrash · « **Reply #13 on:** March 12, 2008, 06:14:10 PM »

My pistons looked like that on my 750 when I pulled them all apart for cleaning.

If it were me looking at that piston. I would try to clean it up and see how it worked before buying a new piston. That's just me though. I'm a cheapskate, and willing to try to clean and fix before purchasing. This sacrifices time, if you have that in abundance. If not just buy it.

If you do in fact have some time to put into it (probably only 3 hours) here's what I would do. Take some 600 grit wet sanding paper, and clean up the piston and the piston chamber in the brake caliper. With the caliper dry (wipe it out with a paper towel) the piston should drop in and out relatively easily while being a snug fit.

Re-assemble, bleed the brakes till they're firm and responsive and determine if the piston retracts successfully when you let go of the brake. Ride the bike down the driveway and see how it feels. If successfull ride it around the block and see how it feels. If you have any binding or brake dragging, you may need to replace the piston. If all is good, ride her like hell.

Best o luck. And please remember that's just what I would do (and have done with more than 2,500 miles of success) with my bike.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #14 on:** March 12, 2008, 06:22:20 PM »

The way I look at it is if the pits traverse the seal then pitch it. If that is the case then the pits will carry brake fluid past the seal. OR you could try to fill the pits with something that is resistant to brake fluid and very carefully sand them down. If the second choice is appealing you need to decide whether you're going to use DOT3/4 or DOT5 to determine what you'll use to seal the pits. Epoxy or JB weld perhaps?? I DO NOT KNOW (my disclaimer). Some of the guys have tried this but I have no experience doing so. My last tear down determined my pits were not an issue since they did not traverse the seal. I then went with DOT5.

Gordon · « **Reply #15 on:** March 12, 2008, 06:44:15 PM »

To answer your question, "is it useable?". Yes.

Is it ideal?, No.

tomswift · « **Reply #16 on:** March 12, 2008, 07:04:13 PM »

my vote is for reuse the piston... but read this carefully:

pull off the caliper and inspect behind the pad after 500-1000 miles. if it is wet with brake fluid, go straight to the ordering place and put yer money down

don't forget... clean out that indented space where the square-ring goes... especially the part you cannot see!!! Gotta use bent tools, I bent a coat hanger, then flattened out a scraping edge. I sell this fine tool on ebay for $75!! <joke>

Seriously, by cleaning out the seal seat you allow it to spread evenly around the caliper body, and then evenly against the piston. Your little pits may allow a miniscule amount of fluid to seep out, but you shouldn't see a "wet spot" unless there's something on the back of the piston I don't see.
Good luck!!
TS99

1975cb550 · « **Reply #17 on:** March 12, 2008, 07:14:55 PM »

yea i can't see spending $80 bux on it. thank for all your input. Tomswift is your bike a cb550? year? it looks a lot like mine. rock on!

tomswift · « **Reply #18 on:** March 13, 2008, 05:32:47 AM »

Yes, it was a CB550K I bought and got back on the road looking good for $500 - it was the 3rd CB550 I have owned

I just pulled this photo up to post, I will replace it with the CB750F project I have started in about a month - yesterday I painted the frame

here is a "before" photo

and here is after...check out the funky blue chain

bozo4onion · « **Reply #19 on:** March 13, 2008, 07:34:41 AM »

Yours looks just like mine. Crap. Just ordered one from honda parts direct. About $65. Thought a new seal would fix my leak. No such luck. Good luck.

crazypj · « **Reply #20 on:** March 13, 2008, 07:57:32 AM »

Quote from: hymodyne on March 12, 2008, 06:09:47 PM

I had a reused pitted piston ruin a trip to lake champlain. the last 150 miles of the trip, I my front caliper rubbed and built up heat... a new piston is well worth the money.

hym

A pitted piston WONT CAUSE BRAKES TO RUB.
It may leak but it wont cause brakes to rub/drag.
Bad adjustment or set up causes that problem.
Even if brakes drag, when pressure gets too high fluid returns to master cylinder
See post about non-return valve for probable cause
http://forums.sohc4.net/index.php?topic=31966.0
PJ

Gordon · « **Reply #21 on:** March 13, 2008, 08:33:17 AM »

Quote from: crazypj on March 13, 2008, 07:57:32 AM

A pitted piston WONT CAUSE BRAKES TO RUB.
It may leak but it wont cause brakes to rub/drag.

So you're saying a rough, pitted, rusted surface on the piston can in no way cause extra drag against the piston seal, thus keeping the piston from fully retracting into the caliper?

I have to disagree.

crazypj · « **Reply #22 on:** March 13, 2008, 08:59:53 AM »

Quote from: Gordon on March 13, 2008, 08:33:17 AM

So you're saying a rough, pitted, rusted surface on the piston can in no way cause extra drag against the piston seal, thus keeping the piston from fully retracting into the caliper?

I have to disagree.

Extra drag means the piston wont extend which will cause it to over-retract, at least until there is enough wear on pads to allow too much movement in lever and you have to pump up brakes to get them to work.
PJ

Gordon · « **Reply #23 on:** March 13, 2008, 09:03:18 AM »

Quote from: crazypj on March 13, 2008, 08:59:53 AM

Extra drag means the piston wont extend which will cause it to over-retract, at least until there is enough wear on pads to allow too much movement in lever and you have to pump up brakes to get them to work.
PJ

But the force applied by the rider, via the MC, to extend the piston inside the caliper is much greater than the force required/applied to retract the piston.

mustangcar · « **Reply #24 on:** March 13, 2008, 09:52:04 AM »

should still be good.just wetsand the fk out of it,with 400 grit then 2000 grit so long as the pits don't scratch the seal,also wetsand the bore and if using an old brake pad the side of holding pad plate,

TwoTired · « **Reply #25 on:** March 13, 2008, 10:01:47 AM »

Quote from: crazypj on March 13, 2008, 07:57:32 AM

A pitted piston WONT CAUSE BRAKES TO RUB.
It may leak but it wont cause brakes to rub/drag.
Bad adjustment or set up causes that problem.
Even if brakes drag, when pressure gets too high fluid returns to master cylinder

I have to disagree with with you on this one, pj.

Although a blocked return will certainly prevent hydraulic pressure release, and proper adjustment is required, that is not the force that withdraws the piston from the disk.
The reason why the caliper seal is a square section seal, is that on brake application the seal square section goes parallelogram before sliding. When fluid pressure is released, it returns to square, withdrawing the piston enough to lose brake pad contact with the disk. The piston doesn't really slide on the seal until pad wear requires it.

When the pits in the piston get large enough, and are under the seal, the seal fills those pits and changes the geometry of the square section, reducing its piston retracting effectiveness. A few small pits have less debilitating effect as as many large ones.
Therefore, when the pits get bad enough, the seal is no longer a square section and the pad rubs the disk.

I've seen badly pitted pistons where the seal still retained fluid properly. But, after a time period of a week or month, the brakes would then drag. Repositioning the seal would cure this... for about a week or month. And then, the problem returned as the seal took a set in its new position in the corrosion pits.

Cheers,

crazypj · « **Reply #26 on:** March 13, 2008, 10:38:28 AM »

Quote from: TwoTired on March 13, 2008, 10:01:47 AM

The reason why the caliper seal is a square section seal, is that on brake application the seal square section goes parallelogram before sliding. When fluid pressure is released, it returns to square, withdrawing the piston enough to lose brake pad contact with the disk. The piston doesn't really slide on the seal until pad wear requires it.

When the pits in the piston get large enough, and are under the seal, the seal fills those pits and changes the geometry of the square section, reducing its piston retracting effectiveness. A few small pits have less debilitating effect as as many large ones.
Therefore, when the pits get bad enough, the seal is no longer a square section and the pad rubs the disk.

I've seen badly pitted pistons where the seal still retained fluid properly. But, after a time period of a week or month, the brakes would then drag. Repositioning the seal would cure this... for about a week or month. And then, the problem returned as the seal took a set in its new position in the corrosion pits.
Cheers,

As you say, the piston in effect 'ratchets' out due to pad wear.
Initially though, the pads over-retract.
The amount of rubbing is never severe enough to cause wheel lock up, usually it only glazes the moving pad.
Almost all the Honda calipers I've looked at 9 and Yamaha ones) have the bottom of the seal groove machined at a slight angle (about 5~10 degrees?) the 'inner' edge is higher than the outer, the seal is angled when fitted and the piston slides in with less force than it slides out. the pressure from fluid helps to seal things up. Worn seals show a 'flat' on one edge/lip only when removed
PJ

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Author Topic: Is my caliper piston useable???? (Read 4418 times)

tomswift

tomswift