GS550 Sudden stuck brake caliper during ride

[salty_monk]

It will likely break if it's as brittle as the one I replaced on my 1000G years ago...

If you want to cut your losses there are more modern master cylinders that will work... For example the one from a KLR 650 works on a single brake GS, plenty of other 14mm bore master cylinders out there and will probably not cost any different to a new reservoir

and yes.... you should replace the lines if they are old stock rubber ones. There is a company a lot recommend on here.. Canadian from memory. You can also make your own using parts from Earls & Nessism's "how to" or order them from Z1 Enterprises as well.

https://www.z1enterprises.com/wheel-brake-tire/brake-line-bolts-fittings-z1enterprises.html

[Isoparmesan]

Managed to get it apart last night (without breaking the reservoir). That little hole is completely rusted through (at least it appears to be rust). I went at it with a guitar string and brake cleaner for about 90 min before sticking it in the ultrasonic cleaner to another 90 min. Barely made any progress.

does the hole go straight through, or is there a bend in it? I couldn’t find the other end of the hole inside the cylinder.

Probably going to look at getting a new master cylinder anyway.

edit: should I steer clear of these suspiciously cheap ones on eBay and Amazon? https://rover.ebay.com/rover/0/0/0?m...2F113360932741

https://www.amazon.com/dp/B07ZPKWMQK/ref=cm_sw_r_cp_api_i_eTcZDbDKJXFD3

edit edit: for $13, I figure one of those cheapies are worth a shot. I've probably wasted more money on less. It may at least function as a stop gap until find a oem (for this bike, or a compatible one) that's in good shape and at a decent price. Or until I chip away all that rust.

[salty_monk]

Even cheaper under different links... I'd be wary of buying something like that just as it's brakes...! https://www.ebay.com/itm/Front-Brake...8AAOSw1Thc2zeF

For my money I'd get something like this: https://www.ebay.com/itm/08-12-KAWAS...UAAOSw8YVaxq0s

or from a 300: https://www.ebay.com/itm/FRONT-BRAKE...0AAOSwAQBayVWu

https://www.ebay.com/itm/17-Kawasaki-Ninja-300-FRONT-BRAKE-MASTER-CYLINDER-lever-mount-oem-ex300-G2/303295114608?fits=Model%3ANinja+300&epid=2103082644&hash=item469dcc2d70:g:8jQAAOSwfyJdiN3j:sc:USPSPriority!90505!US!-1

I have an upgrade for the single rotor models using a Blackbird rotor & a Concourse/Ninja twinpot caliper, I thought I'd point you to it as you're looking at brakes. Makes a massive difference (for the hills of San Fran )

https://www.thegsresources.com/_forum/showthread.php?222546-Twinpot-Brake-Upgrade-on-GS550E-GS750C-GS1000C&highlight=

[Isoparmesan]

Ah, yes. I have considered your radical looking front brake upgrade! Potentially a future project. And, it looks like I pulled the trigger on that $13 brake cylinder mere seconds before you recommended against it. I'll update this thread with the results.