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master cylinder - 81 GS850L

  • Thread starter Thread starter remo
  • Start date Start date
R

remo

Guest
im having a problem with the master cylinder, hoping someone can lend some advice. im not getting any compression from the front brake system, so i checked right at the master cylinder connection, and didnt feel any compression there either. i assumed i needed to rebuild it, but when i disassembled it, i couldnt get into where the piston is to rebuild it. i did notice alot of rust and gunk inside, so i took as much apart as i could, cleaned it all up, filled it back up with new fluid and... nothing. the brake lever pulls all the way in, but no fluid comes out, and theres no resistance against the lever. im assuming i still need to rebuild the cylinder, or do you think its worth it just to buy a new one and be done with it?

thanks for any and all help!

ps on the same note, the pistons in the front brake calipers are seized, any advice on getting them out will be appreciated as well.
 
There's a snap ring holding the piston set in. You have to get that out first. Some skinny dollar-store pliers with the tips ground to a fine point might help. If the bore is pitted then you should probably get a new master cylinder. Look for a good used one here, or find one with the same or similar size bore meant for 7/8" handlebars. Bore should be 5/8", 16mm is close.

Several threads recently about stuck caliper pistons. Like this one:

http://www.thegsresources.com/_forum/showthread.php?t=181073
 
I agree with continuing disassembly. Rust on the outside does not necessarily mean pitting in the bore. Cliff has a write-up on the front master that may be of some help. bwringer has found a set of snap ring pliers that are slender enough and have enough reach to get in there. I ground down a set of needle-nose pliers from Harbor Freight before I saw that. The factory service manual for your bike on Cliff's site has a cross section view of the master that may help you see how to get it apart.

It may feel like throwing good money after bad, but I'd recommend rebuilding any replacement master you may get from eBay or wherever or even another GSR member. You never know what abuse they may have suffered over 30 years, and this is a key component of your most critical safety feature.
 
okay thanks guys. im re-inspired to disassemble it again tomorrow and give it another shot.
 
so when i disassembled it again, i noticed that there was actually alot more rust and crud that needed to be cleaned out. so i gave it a very thorough cleaning this time, paying particular attention to the small port where the fluid enters the bore. so i reassembled it, and before i reattached it onto the bike, i submerged it in brake fluid and pulled the lever. i could now see bubbles which means its working. which is great. then i had the problem of the stuck caliper pistons, so i figured i could just clamp the brake lever down and it would force the pistons out, as ive read other people having success with this method. but when i did this, after everythings connected, i still have the same spongy feeling from the brake lever. i disconnected the banjo fitting at the master cylinder, and put my thumb against it, there is still compression there and fluid squirting out, so i know the cylinder is working now. im thinking there must be a leak in one of the hoses somewhere down the line. am i on the right track or is there something im missing?

thanks for any and all advice!
 
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