Front disc on rear...

[postman_pat]

Huh, the '83 550 has a smaller disc than the '78 rear disc?

That is correct. The 1983 GS(X)550 has two 260mm diameter discs at the front. Both are 5mm thick, 4.5 mm min thickness, slotted pattern.

http://www.metalgear.com.au/view_model_details.php?model_id=9062

[salty_monk]

I assume the offset is the same & it's centred between the pistons ok...?

If so at that point it can only be heat soak / transfer. What else is there?

[tkent02]

I assume the offset is the same & it's centred between the pistons ok...?

If so at that point it can only be heat soak / transfer. What else is there?

yes, it all looks good and I rarely use the back brake anyway.

[AxelP]

To hi-jack a tread. I had similar experience with another bike( Yamaha Virago 750) and front brakes. After winter storaging in the relatively warm and humid enviroment (underground parking lot) I was trying to ride it to my home and after few miles brakes seazed. First it feels like small drag then more more and more until it gave enough drag to stop bike. So I just bled some amount of brake fluid through the caliper nippel and it released brakes and allowed me make it home.
I believe that moisture made it's way in to the fluid and increased internal volume which increased pressure in the system and created drag. Moreover it is possible due to the weather conditions bringing bike from relatively cold garage to warm outside may helped too.

[Steve]

... I was trying to ride it to my home and after few miles brakes seazed. First it feels like small drag then more more and more until it gave enough drag to stop bike. So I just bled some amount of brake fluid through the caliper nippel and it released brakes and allowed me make it home.
I believe that moisture made it's way in to the fluid and increased internal volume which increased pressure in the system and created drag. Moreover it is possible due to the weather conditions bringing bike from relatively cold garage to warm outside may helped too.

No, what likely happened is the equalizer port in the master cylinder plugged up. It's a tiny little hole that is easily plugged, and when it happens, it can not allow warmed-up brake fluid (normal, while riding) to expand back into the reservoir. The only place the fluid can expand is by pushing on the piston(s), which creates more heat, causing more expansion, etc., leading to your lock-up.

It's easy to clean the equalizer port. Just get access to it, then try blowing air through it. If that doesn't work, spray brake cleaner through it. If THAT doesn't work, use a single strand of wire to poke your way through the crud, followed by brake fluid and air. Finally, be sure to flush the entire system, to prevent it from happening again.

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