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82 GS650G Master Cylinder Rebuild

  • Thread starter Thread starter 92G
  • Start date Start date
9

92G

Guest
I've noticed that my front brake has a little fade in it "sometimes" when using really low brake pressure. It never fades if I grab it hard. This leads me to believe a seal has low pressure leakage in the master cylinder.

Do I need to order anything other than the piston-cup set in the parts list to rebuild it? Also, Can anyone give me the instructions?

Do you think it's the master cyl, or am I barking up the wrong tree? I've already flushed(replaced all of the old fluid), and bled calipers.

Thanks,

Terry
 
I see that no one jumped on this to give any suggestions. I don't know about rebuilding the master cylinder on your particular bike, but... You said that you changed the fluid and bled the brakes. Was there a brake fade before you changed the fluid? If not, then you have air traped in the system. Often, to properly bleed a master cylinder you need a vaccum pump bleeder to get the air out and purge the system.

If you have spongy feel in the brake lever, its traped air. When I rebuilt my master cylinder it was only the "O" rings and seals that needed to be replaced. Good Luck!
 
Thanks for the advice.

The low pressure softness was why I exchagned the fluid. I found a NOS Master Cylinder on Ebay for $40, so I'm not going to worry about rebuilding the old one.

Unfortuately, it is slightly different from my original in that the fitting is on the end instead of the back, so I need a new brake line with the banjo fitting rotated 90deg.

Terry
 
92G said:
Thanks for the advice.

The low pressure softness was why I exchagned the fluid. I found a NOS Master Cylinder on Ebay for $40, so I'm not going to worry about rebuilding the old one.

Unfortuately, it is slightly different from my original in that the fitting is on the end instead of the back, so I need a new brake line with the banjo fitting rotated 90deg.

Terry
Click to expand...

I've also had problems bleeding the brakes after installing new lines or anytime I had the system completely drained. The symptom is that the brakes feel spongy on the bottom end but work ok with more pressure.

I have found that this has been caused by air trapped near the banjo bolt. I have had to crack the bolt several times, pumping up pressure and holding it for a few seconds in-between each crack. The idea is to have a helper pump up the brakes and hold pressure on them while you crack the fitting and retighten it quickly enough to bleed the system slightly but not enough that you totally loose pressure on the system and draw air back into the line. I usually wrap a rag around the fitting while I do this to keep from getting brake fluid spilled on the bike.

Mike
 
Re: bleeding brake lines. I have found that tapping the whole brake system lightly with a rubber mallet can loosen any air bubbles clinging to the inside of the system before you open the bleeder valve.
 
mdole said:
...I have found that this has been caused by air trapped near the banjo bolt.
Click to expand...

Good advice.... Same for the tapping. I'll give it a try.

Thanks, :)

Terry
 
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