Stuck brake caliper

[KRISTI'SGS550]

As you all are aware of I have been having troubles with my front brakes on my 1982 CB650. I have cleaned everything, replaced all O-rings, rebuilt the calipers, replaced the brake line and added new fluid. The caliper is functioning correctly. I attach a clear tube to the breather nipple and compress the brake lever. As I compress fluid comes out, when I let out the brake lever fluid goes back into the opening. So this tells me it is functioning correctly.

My problem seems to be the cylinders inside the calipers. They don't seem to want to budge. When the calipers are off I can hammer them in with a hammer and than push about 150 psi through the bleeder to shoot them out. But I can't move them with my hands, and my manual says I should be able to move them freely by pushing them in with my hands.

Can I put some sort of grease on these cylinders and new O-rings to help them slide better? I have smoothed the bore and cylinders but I think my problem lies between the cylinders and the O-rings, just too dry to operate. When I first put everything back together I used brake fluid, but it didn't seem to work.

Any suggestions are appreciated. We have figured out everything else on both bikes, just have these brakes to go and the bikes are on the road ready to scream.

Cory

[p_s]

The front calipers on my GS were tormenting me last week. Finally I found that compressing the pots all the way in with a clamp got me most of the way there (bad drag but rideable) and then mounting the calipers, loosening the axle and the lower fork nuts on both sides under the axle, bouncing everything around, tightening it up, and my brakes are prefect.

When the calipers are off, you should be able to squeeze the lever and see them come out and then retract slightly. If not your seal might be bad or contaminated.

[KRISTI'SGS550]

My seals are brand new, I think that is the problem, the seals and the cylinders that push the brakes are sticking or stuck. When I compress the brake lever, nothing happens.

Cory

[p_s]

My seals are brand new, I think that is the problem, the seals and the cylinders that push the brakes are sticking or stuck. When I compress the brake lever, nothing happens.

Did you get anything on the seals besides brake fluid? Er, also a hammer shouldn't be used when rebuilding brakes.

[TooManyToys]

First, where did you get the rebuild kits? Are they factory?

You should be able to push the pistons in with your thumbs. The square cut O-Rings fit into a tangential groove, with some slop in the normal caliper piston direction. As you apply pressure, the O-Ring and piston moves forward, compressing the O-Ring in the tighter bore of the tangential groove, sealing better. The ring distorts as the piston moves forward and then "rolls back" when pressure is released. Thats how the piston retracts, with the O-Ring returning from it's distorted shape. The hardness of the O-Ring and it's sizes determines the amount of seal roll back for the piston and intimately, pads. The only time there is any slide motion between the O-Ring and the piston is when the piston moves up due to pad wear.

If the O-Ring is the wrong size, or the wrong durometer hardness (possible with aftermarket parts), then things won't work as they should. The other possibility is if there is any corrosion in the tangential bore where the O-Ring resides, whcih would cause the O-Ring to fit much tighter then it was intended to be.

As another person mentioned, any petroleum product on these rubber parts will cause them to swell, which could also be the issue.

[KRISTI'SGS550]

No, I didn't use anything else besides brake fluid. That is my main question. Do I need to use grease or something on my rings and cylinders to make them slide better?

I used the hammer to get the pistons and brakes to get together, otherwise there was no way to get them moving. I did use a piece of wood against the brake pads and then hit the hammer, hopefully that is better.

Cory

[Nessism]

First, where did you get the rebuild kits? Are they factory?

You should be able to push the pistons in with your thumbs. The square cut O-Rings fit into a tangential groove, with some slop in the normal caliper piston direction. As you apply pressure, the O-Ring and piston moves forward, compressing the O-Ring in the tighter bore of the tangential groove, sealing better. The ring distorts as the piston moves forward and then "rolls back" when pressure is released. Thats how the piston retracts, with the O-Ring returning from it's distorted shape. The hardness of the O-Ring and it's sizes determines the amount of seal roll back for the piston and intimately, pads. The only time there is any slide motion between the O-Ring and the piston is when the piston moves up due to pad wear.

If the O-Ring is the wrong size, or the wrong durometer hardness (possible with aftermarket parts), then things won't work as they should. The other possibility is if there is any corrosion in the tangential bore where the O-Ring resides, whcih would cause the O-Ring to fit much tighter then it was intended to be.

As another person mentioned, any petroleum product on these rubber parts will cause them to swell, which could also be the issue.

This post pretty much sums it up. Something is wrong with your seals and/or the groove has crud in it - you should be able to push the pistons in with your hand.

Brake fluid only upon assembly. Pads sometimes slide on a pin(s), a little high temp grease is appropriate here. Also, the pin should not have grooves or steps which allow the pads to hang up on.

Good luck.

[KRISTI'SGS550]

The pads move freely, it is definately the two cylinders within the brake caliper (not master cylinder) that are the problem. Just wondering if I can grease them up so they will slide better against the new O-rings?

Everything is about a week old and factory.

I am not sure if you all noticed it's a 1982 Honda CB650, not a GS.

Cory

[Nessism]

The pads move freely, it is definately the two cylinders within the brake caliper (not master cylinder) that are the problem. Just wondering if I can grease them up so they will slide better against the new O-rings?

Everything is about a week old and factory.

I am not sure if you all noticed it's a 1982 Honda CB650, not a GS.

Cory

No grease.=;=;=;

[KRISTI'SGS550]

No grease.=;=;=;

Do you have any suggestions of how to make them move freely? Without having to use a hammer or 150psi of air? The brake fluid doesn't work, it just dries it up and makes it worse.Cory

[KRISTI'SGS550]

[quote=TooManyToys;795593]If the O-Ring is the wrong size, or the wrong durometer hardness (possible with aftermarket parts), then things won't work as they should. The other possibility is if there is any corrosion in the tangential bore where the O-Ring resides, whcih would cause the O-Ring to fit much tighter then it was intended to be.

The O-rings in the brake caliper before the new ones did the same thing, so I assume both are factory rings. The only conclusion I can come up with is I need to clean the channels the O-rings fit into again. Maybe I will get some of those scraper toold dentist use and try them?Thanks for the explaination, it was great!Cory

[p_s]

Just for the heck of it, take out the seal from the caliper and make sure the piston moves easily in the bore, and then that the piston moves easily in the seal.

[Guest]

dunno if your case, but if the brake pads are totaly worn out and then the bike is left to sit for a long time the piston may develop corrosion
and when you reassemble the lot they wont slide in readily
other than honing the piston cylinder and smoothing the piston, sometimes a new piston is required

[Zooks]

I have rebuilt dozens of calipers using fine emery paper to remove the crud and gum. After all of the crap is cleaned out, reassemble the caliper using decent amounts of caliper lube. Caliper lube is basically liquid silicon. It feels a lot like KY in texture (don't use it in the bedroom) and helps everything slip and slide nicely. I have a small 'squeezy' bottle of it in my workshop and use it to slide all sorts of mechanical things together.



Any of these will do the trick nicely. There are also dozens of 'generic' lubes that will also do the trick. Just make sure they don't effect rubber. Normal grease is mineral (petroleum) based and is not good for rubber seals and 'o'-rings. You want one that is silicon based if possible. Do not use vaseline (petroleum jelly).

[Nessism]

I have rebuilt dozens of calipers using fine emery paper to remove the crud and gum. After all of the crap is cleaned out, reassemble the caliper using decent amounts of caliper lube. Caliper lube is basically liquid silicon. It feels a lot like KY in texture (don't use it in the bedroom) and helps everything slip and slide nicely. I have a small 'squeezy' bottle of it in my workshop and use it to slide all sorts of mechanical things together.



Any of these will do the trick nicely. There are also dozens of 'generic' lubes that will also do the trick. Just make sure they don't effect rubber. Normal grease is mineral (petroleum) based and is not good for rubber seals and 'o'-rings. You want one that is silicon based if possible. Do not use vaseline (petroleum jelly).

Those lubes are for external parts on the caliper: sliding pins, back side of brake pads, etc. Do not use those lubes on the internal parts like the piston and seals. The Suzuki service instructions are very clear, brake fluid only on internal parts.


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