1977 GS550 front brakes

[DennisDW]

On my 77 550 the front brake will start clamping the calipers while sitting. I've had it where I drive the bike to work and things are good and after work I get on the bike and the front brakes are on. I bleed the caliper and things are fine again. It doesn't happen happen all the time. It might go two weeks just fine and then all of a sudden they will be tight after sitting for a while. Is it my master cyclinder? I've had it apart and things look pretty normal. Is there a rebuild kit for a master cyclinder?

Thanks for your help
Dennis DW

[Nessism]

Could be the master or the caliper. I recommend a complete system tear down and clean out. Line should be replaced if it's old since they develop a scale on the inside. OE part sources sell parts. Do a search for various options such as Bike Bandit, Flat Out Motorcycles, motogrid.com, etc.

[Old Colt]

This sounds like the master is not returning properly. Make sure nothing up at the lever is sticky or binding. If nothing up there jumps out as being wrong you need to take both the caliper and master apart and freshen the seals.
Not knowing when or if they were serviced last it would be good to do so.

[rapidray]

It is also possible, with air in the lines, that if it went from your garage in the shade to sitting in the sun at work, that the air could heat up in the lines & expand & hold the brakes on. Not common, but possible. Ray.

[Suzuki_Don]

Fefurb both master and caliper. Ensure all holes in master cylinder are clear with no blockages. Especially the small bleed hole. Fit new stainless brake lines and all new seals and piston kit in MC and caliper. Make sure caliper is not sticking on slider pins. Remove, clean and grease with special caliper grease before reassembly.

[DennisDW]

Thanks for your ideas. I've had the caliper apart 3-4 time looking for things that could cause it to tighten up. I've had the master cyclinder apart once and 2 of the 4 holes in the cyclinder were plugged so I thought I had it figured out but it still did it after finding that. I'll do some checking to see if I can find the problem. The part about air in the lines and expanding when warmed up makes sense so I'll make sure all fittings are tight. I'll maybe look into the MC again to make sure everything looks clean and loose.
Dennis

[hampshirehog]

This happens if you get DOT5 brake fluid mixed up with even a trace of DOT3 or 4. PITA if that's the cause - complete clean (and I mean a deep, complete clean) or new bits is the only answer.