Author Topic: CB550 Brake Caliper Issue (Read 1788 times)

Paul E. · « **on:** July 16, 2019, 08:31:04 AM »

My brake caliper piston is not retracting when I squeeze the brake lever. If I tap on the flat body of the caliper, the piston will retract allowing the swingarm to move left and right. Grabbing the brake lever another time, clamps the brake pads against the rotor again. I don't think the piston and caliper are binding, but I'm not sure what's preventing the piston from retracting.

I took the bike around the block to see if the rotor would float the pads back to the middle, but it did not change anything. The rotor became quite hot; a licked finger sizzled when touched against the face, and the drag was very noticeable while riding.

Additional information

This is with brand new EBC brake pads, paint filed off so they drop in smoothly.
The piston itself is clean and free of pitting.
Piston installed with Raybestos assembly fluid and the nylon backing washer. Piston cap facing out.
Applied Dow Corning to the caliper side walls - not the piston bore.
Set stationary pad clearance to 0.006 in. with the adjuster spring prior to bleeding the brakes.
Saw bubbles coming from the master cylinder return hole during bleeding.
Stainless steel lines.

With the old brake pads, the adjuster screw was backed off to the point that it was not engaged.

ekpent · « **Reply #1 on:** July 16, 2019, 08:49:44 AM »

Crack open the bleeder next time it starts to seize and see if it releases. Still could have a blocked return hole in the master.

bryanj · « **Reply #2 on:** July 16, 2019, 09:45:00 AM »

Did you clean out the seal groove scrupulously before fitting new seal?
Small hole in master could be blocked
Flexible hoses could be collapsing internaly

Paul E. · « **Reply #3 on:** July 16, 2019, 09:30:37 PM »

I cracked the bleeder valve after it started to seize, no fluid came out. Squeezing the lever with the bleeder still cracked, made some brake fluid came out.

I believe this means the fluid behind the piston isn’t under pressure. So something else is keeping the piston from retracting, perhaps the seal?

I picked up a e guitar string and threaded it into the MC return hole. This did not release the piston, but it did free a tiny bubble.

bryanj · « **Reply #4 on:** July 16, 2019, 11:54:55 PM »

Sounds like you have secret additive in the seal groove(krap) NOTE you need to clean it out with a tool like a dental pick a dremmel brush just polishes the krap and leaves it there, new seal is a good idea and they dont cost much

ekpent · « **Reply #5 on:** July 17, 2019, 08:16:41 AM »

What you wanted to do was to see if the caliper freed up when you cracked the bleeder and not what came out of the nipple. If it freed the caliper then you can work upstream to find the problem. If the caliper stayed stuck or sticking I would start there.

Paul E. · « **Reply #6 on:** July 17, 2019, 06:54:41 PM »

I picked up a new seal on the way home. During disassembly, I noticed the old seal has a small raised bit in the middle. Looking at the groove in the caliper body, it appears there is a small channel inside that groove. The raised portion on the outer edge of the rubber seal must have come from it. Is this standard for these caliper bodies?

Went after the groove with dental picks. There wasn't much that came off but I'm going to install the new seal and see if it helps.

bryanj · « **Reply #7 on:** July 17, 2019, 09:27:44 PM »

First picture i can see crud in the groove, last picture a lot better.
Never seen a seal ridge like that and have never noticed a groove in one.
The groove is machined to slightly distort the seal into a diamond shape so just a corner seals, it is the "twist" in the seal that pulls the piston back into the caliper.

Paul E. · « **Reply #8 on:** July 18, 2019, 06:29:11 AM »

Pads are continuing to seize with the new seal and freshly cleaned caliper. Cracking the bleeder valve did not free the caliper.

Whacking the caliper body with a rubber mallet freed the rotor and I could spin it by hand.

To test if the piston was retracting at all, I removed the caliper from the swingarm and then squeezed the brake lever.

For each pump, the pad would advance forward, releasing the brake lever would retract only 10-20% of the amount it advanced.
I repeated pumping it out and using a C-clamp to press it back in a few times, but it never seemed to retract more than that 10-20%.

Not sure what to try next

BenelliSEI · « **Reply #9 on:** July 18, 2019, 06:38:12 AM »

Paul..... the piston only has to retract a very small amount to release the pads from the disc.
How old are your rubber brake hoses? I’ve had a set that deteriorated so badly they were acting as a check valve. Pressure from the master forced fluid to the caliper, but the hoses were so choked up it took forever to relax......

Little_Phil · « **Reply #10 on:** July 18, 2019, 06:43:44 AM »

Quote from: BenelliSEI on July 18, 2019, 06:38:12 AM

Paul..... the piston only has to retract a very small amount to release the pads from the disc...

Exactly, only 0.006 will release the disc. A full pump of the lever will advance it far more, but as long as it retracts 0.006" it should free up when in use.

Paul E. · « **Reply #11 on:** July 18, 2019, 06:58:49 AM »

Well hey, it might be retracting the correct amount then. It was advancing about a 1/16" at 10% retraction we are right around 0.006 in.

The rubber lines got the boot back in 2012, I put on some braided stainless steel lines from Shaun at Slingshot.

BenelliSEI · « **Reply #12 on:** July 19, 2019, 06:00:55 AM »

The other thing that assists this process is “knock-back”. Your disc usually has a high spot that kicks the pads back too. If you can roll the bike easily after a brake application, your done.

Paul E. · « **Reply #13 on:** July 19, 2019, 01:43:21 PM »

Dial gauge on the brake rotor shows 0.003 in. difference with one full rotation. Is that acceptable, or should it be 0.000?

Last night I disassembled, cleaned, and greased the caliper swing arm. After bleeding, I had a little progress where I could move the front wheel after applying the brake lever. It still took a lot of force to rotate, definitely isn't free spinning.

Knocked the back of the caliper to reset the pads and rode it down to the gas station, using only the rear brake. Checked the front rotor, it was still sizzling hot. But it did seem to roll better.

Master cylinder rebuild kit has arrived so that's next.

Is there a way to align the brake pad faces? I noticed the feeler gauge will be loose at the front but experience drag towards the back of the bad, closer to the engine.

Bankerdanny · « **Reply #14 on:** July 19, 2019, 02:04:59 PM »

You area very very unlikely to ever get a rotor that is absolutely flat with no runout.

Paul E. · « **Reply #15 on:** September 01, 2020, 08:29:48 AM »

Returning to this thread, my stuck brake pad was caused by fitting too tightly inside the brake caliper housing. I had removed all the paint from the EBC pads, but I had to continue removing metal to get it all to work. Hopefully, this can save someone else some headaches.

Does anyone have suggestions on a suitable sealant for the exposed metal on the brake pads—that won't contaminate the brake pads as well? I imagine that bare metal is rusting away as I type.

bryanj · « **Reply #16 on:** September 01, 2020, 01:24:28 PM »

Coppaslip grease

Deltarider · « **Reply #17 on:** September 02, 2020, 07:52:00 AM »

Or Ate or similar.

Paul E. · « **Reply #18 on:** September 03, 2020, 07:22:05 AM »

Appreciate the suggestions, I'll if either are available locally.

I do have some Dow Corning high vacuum grease, but it's thick—seems like you would want something that would lubricate the brake pad moving in and out of the caliper.

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Author Topic: CB550 Brake Caliper Issue (Read 1788 times)