LF200GY-2 rear disc seizing

[TheLoneRoger]

About a year ago without warning my rear disc starting seizing up as I was on my way home; by the time I found somewhere to pull in it was locked up and smoking - iirc, after half an hour it had cooled down enough to ride cautiously the rest of the way home.
As it was so cheap, I replaced the whole assembly and it's been good as gold since - until two days ago, when it happened again, in almost exactly the same place give or take a 1/2 mile!
This time I had pulled in for fuel anyway and it only took a few minutes to cool down enough to ride away.
So, any ideas what's up with these brakes? They may be cheap compared to Jap parts, but not if you have to replace them every year!
Is there any maintenance I should be doing to keep them from crapping out like this?
Cheers
Roger

[david3921]

Does it seize after applying the brakes? If so, the fluid is not returning to the MC correctly. It may be blocked somewhere. Try bleeding the brakes in reverse, pumping fluid through the caliper to the MC. You may see some debris. Maybe the problem is in the brake line. Is it rubber or steel braded? If it is rubber it may be deteriorated and allowing debris to clog the MC. Make sure that the brake fluid you use is new and clean, also.

[Weldangrind]

Is the bike normally stored outdoors? Perhaps the caliper is a little rusty. If all else fails, find a new riding area that has better luck.

[FastDoc]

This happened on Ron's GY2 and we have seen this here before here on CR. In Ron's case the rear wheel locked up at about 50 MPH and he skidded safely to a stop on a country road, thank God.

IIRC the resevoir was overfilled in China and left no room for expansion.

I changed the fluid, inspected the caliper, rotor, and pads and it was good to go.

[Wild_Alaskan]

the most common cause of this on hydraulic brakes is a poorly adjusted master cylinder, the master cylinder MUST be allowed to fully extend, otherwise if the fluid boils or otherwise expands it can not flow back in the the cylinder even though the brake is not being pushed so it expands the only place it can which is pushing out the caliper (making any heat problems worse)

The adjustment for the rod pushing on the master cylinder is solely for compensating changes in pedal height not for adjusting how soon the break engages. a properly bleed system will engage quickly with out forcing the master cylinder to be compressed. running with the master cylinder compressed also will not allow the system to properly compensate for pad wear either as it will not pump its self up like a properly adjusted system will.

[Weldangrind]

Excellent info, WA. I hadn't thought of how over-filling a master might impact the caliper.

[TheLoneRoger]

Thanks - lots of useful stuff there.
Thinking about it, both times it happened on an unusually hot day, so fluid expansion sounds likely.
Also the rubber boots protecting the pins that the two halves of the caliper slide on had melted clean off by the time I stopped last time, and I notice this time that the top one has more or less gone completely and the bottom has perished, so I'm guessing a load of dust and stuff has probably got in there, making it likely to stick.
I'll change the fluid and give it a clean - also think about moving the reservoir; where it is now, it's at a crazy angle 'cos the feed pipe doesn't seem long enough...
Cheers
Roger

[SpudRider]

I agree with FastDoc and Wild Alaskan. ;)

[katoranger]

I replaced mine with a modified honda cbr600 master. Never had a problem again.

[Aj1]

LoneRoger,

Back in college my roommate had a Yamaha R1 that had this exact problem. The only
Difference is that it was on the front wheel. Well I took apart and cleaned both calipers, the master cylinder several times and blew the brake lines out with compressed air hoping
That maybe something was stuck within. No e of that worked and finally in a last effort I had him buy new brake lines and it fixed the problem. It was weird because they were definitely not blocked. Anyhow hope this helps somehow. It was the first time I had ever heard of something like that.