GS500 back brake issues

[Shay HTFC]

Ok... Ever since I've bought this bike, the back brake hasn't worked properly.

I replaced the pads and cleaned out the brake pistons etc, but couldn't bleed them. Tested everything (as per a previous thread) and decided that the master cylinder was bust.

I've just got a new one, but the same problem exists.

Now, this is hard to explain, but I tried playing with my old one and when I replicated the bleeding process (used my fingers to cover the entry and exit holes and test the pressure and vacuums that are created when pushing the arm in and out)

I learnt that the master cylinder essentially 'blocks up' when the arm is pushed only a little bit in (I blew down the pipe that comes from the reservoir and after the push arm bit went in just a tad, it blocked my blowing).

Now my theory is that when the brake is off, the master cylinder isn't actually fully released, in that the through passage from the fluid reservoir to the brake line is still blocked and therefore not sucking fluid down the pipe.

Not sure if I rambling or even understandable, but the master cylinder worked when I was trying it out in my hands using my fingers to block off holes and test out the suction and vacuums that are created.

What do I do? As far as I can tell, the arm needs to come right back out, but the brake mechanism is keeping it pushed in a bit and I can't seem to adjust it as the brake lever and 'rear set' seems to be locked in place.

Anyone ever had a similar issue or got any tips?
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Full Motorbike License - GS500E '95

[Shay HTFC]

EDIT: Just been for a better look and it seems I need to adjust some of the nuts on the 'arm'. Just gonna have a play around with that.

The master cylinder definitely works. I've just unattached it from the brake lever and let the push rod go out to its fully extended length and manually pushed it in and out and the bleeding process works fine.

Only I think that the pushrod is at its most extended already. I might have to cut some of it off, but that doesn't seem right!

(I'll try and get some photos to explain what its like later because this is hardly easy to understand and picture )

EDIT:
Added a video with a bit of commentary
https://www.youtube.com/watch?v=jb7pJFX0Gfg

As you can see, the rear brake lever is as high as it goes. Infact, it's too high and should be lower. But making it lower involves pushing it down and just makes the problem worse.

How can I make the push rod come further out even though it is as far out as seems possible? I've read two manuals and the net and it says that you should just adjust the adjuster nut. Doesn't give any more info.

All I can think of is cutting the push rod and making it shorter!
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Full Motorbike License - GS500E '95

[Thom]

Hmmm i wonder...

I have a GS500 fromm 1990 and i have a problem with my rear brake. i press it a canny way (3-5cm) before i feel any resistance (however it seems to work the brake slightly)

I don't think i bled the brake wrong so i wonder if by tightening those bolts i can make the brake more effective...

Let me know how you get on!
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Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[Shay HTFC]

Well I've been looking through the manual thoroughly and on other things that aren't directly related to the brake pedal. It turns out there is a pinch bolt that determines the position of the brake springs etc AND the bracket that the master cylinder connects to.

I don't have the right allen key to take of the whole footrest bracket , but hopefully tomorrow I can get hold of one, take off the pinch bolt and put it back on a slightly more rotated angle which should have the master cylinder bracket pulled further away. Will get my brake pedal in a better position too hopefully.

I've attached a pic of the pinch bolt and the mechanism around that area.
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Full Motorbike License - GS500E '95

[Shay HTFC]

Just to bring this to a close and complete the 'story' for any others who might search for this... I ended up taking off the whole footrest bracket and on the back side, there is a shaft. I took off the 'pinch bolt' and just spun it round a few degrees and put it back on the shaft.

Now my brake pedal is at the perfect height and the push rod on the master cylinder goes out to its maximum 'out' position perfectly.

I'm soo happy now to have it sorted after so long!
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Full Motorbike License - GS500E '95