CB 650C brake problems

nashbuilder

nashbuilder

Active Member
Ok long story short - My 81 CB650C has been sitting for 5 years. I went to move it and the front wheel would not move. I had pressure in the master cylinder. I thought if I released the hose from the master cylinder it would take the pressure out and allow it to move. That didnt work so I just took the caliper off. I discovered the piston is stuck. Trying to push the piston out with the MC I have bolted the hose back to the MC and to the caliper and I have attempted to bleed the brakes. I have not been successful with this. Any ideas of what could be the issue?
 
probably just a ton of gunk & corrosion that has it locked up. you will need a new piston if it's that stuck so don't sweat getting some lockjaws on it to snatch it out after a good loNg soak in wD-40 & or k-1 . full caliber rebuild too!
 
Are you able to get a look at the piston itself? Scored? Rusty? One thing you REALLY dont want to do is force it, especially if its rusted. How did the brake lever feel before taking the caliper off? Firm? Spongy? fluid color?
 
Drain the caliper and fill it with a mixture of pb blaster and trans fluid. Soak over night. New pistons are 15 bucks or so. Buy a new one. Grip it with some vise grips and wiggle it until it breaks free. Order a full rebuild kit as well. They're cheap.
 
The brake lever was firm, didnt seem to have any problems prior to this piston locking up. I am more worried about the MC problem then just getting the piston out. I dont mind buying a new piston and replacing that. I might just have to do all new MC, Piston, and rebuild kit for the caliper. But if I can work around having to do all that I would like to right now. I am just trying to get the bike running and stopping before I put money in to it.


Here are some pictures of the piston. I tried pushing the piston back in with a C Clamp and it would not budge. I wonder if it is all the way in already?
 

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ok! Thats pretty bad! Definetley want to take your time getting it out. I did see pistons on ebay and I'm sure even your local dealer will have them. I'm curious to see what the inside looks like since you cant even get that piston to move. Remove the caliper, if you havent already. It'll be way easier to work on off the bike. doesnt matter if you use PB blaster, or my favorite skin so soft, youre going to have to let it soak. Maybe this is a good time to upgrade to a dual piston caliper.
 
The nissan is an upgrade for sure, but you can probably get one for less unless you like dimecitys style. Theres always used too.
 
What should I soak the caliper in? Its painted and I don't want to have to re paint. I think I am going to hold of on a new MC until I get the piston out clean it up, the caliper, and take the MC apart and clean that out. Then if its still not working I guess I will invest in a new MC.
 
I'd hit it with brake clean first to get it all as clean as possible. You can soak it in pb blaster. Its paint safe as far as I know.
 
So I took the MC off last night and this is what I found. No wonder my piston is stuck. Someone has offered to give me a good 80's xs650. I have a CB650 do you think that will work on my CB? If not then I think I am going to get the Nissin and a set of clubmans soon.
 
It should fit no problems. Free is always best! Your picture didnt come thru but I'm sure it was ugly. I'm a firm believer in brakes and bearings as the best bang for your buck upgrade on old whips.
 
Yeah I think I am going to go with the freebie first and get the bike up and running smoothly then do my upgrades. My reservoir was starting to rotting away, that is what all the white powder in the picture is ( I believe).
 

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Ok so I got a used MC and bolted it on. Hooked up my lines and hooked up the caliper with the stuck piston. I do not have the whole caliper on, just the main part not the brake pads or brake housing ( not sure the technical term). I attempted to bleed the brakes and build pressure back up in the system to no avail. It is pushing the fluid through because I had to fill more in the MC. I just cant get it pressurized. Any ideas?
 
Yeah... if your mastercylinder looked like that I'm sure the caliper is fracked too. But disconnect the line at the caliper and give the break lever a squeeze to see if fluid comes out of the line. Youre better of not bleeding it since you still need to settle the stuck piston issue. Brake fluid ansorbs water from the air... yep.. right out of the air... and retains it. Since you have to remove the caliper for a time, you're just going to have to repeat the whole fill and bleed process again.
 
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