I have done the RGM conversion to the smaller diameter master cylinder. The conversion went well, I have a milling machine, so was able to drill & tap the master cylinder perfectly before fitting the kit.
Problem now is that it refuses to bleed. All new pipework, pistons and seals, but try as I might, all I'm getting is a few bubbles rising from the master cylinder. Any ideas as to what might be the problem?
I did this mod a while ago…
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Piston adjustment
I took a guess at the position of the plunger, that might be my problem, how could I tell?
I did blank off the outlet from the master cylinder when I i assembled it and it did give me some resistance when pumping the handle.
I have a syringe that I tried pushing fluid from the bleed nipple up to the master cylinder without success. I slackened off the pipe coupling at the caliper to check the oil was getting that far with the syringe. I did get oil, but it did require quite a bit of pressure!?
All the pipes are new, so I shouldn't have any blockages.
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Did you fill and bleed the m…
Did you fill and bleed the m/c before connecting it to the pipework? Easy done by blanking the outlet with the supplied 3/8" bleed nipple and working the lever till there is no more bubbles rising in the reservoir. This takes a bit of time but when done correctly you will have a solid lever. Then fill the reservoir and fit the diaphragm and cap. Upend the M/c so the bleed nipple is at the top then remove it and connect the m/c to the flexy pipe keeping the lever at the bottom and connection at the top. This keeps the fluid in the m/c and prevents air getting in. fasten M/C to handlebars. Use a pressure bleeder fitted to the m/c to bleed the pipe and caliper.
The adjustable piston pusher in the RGM kit makes 'tuning' the m/c an easy task. A quick way to set the pusher at the optimum length is to push the caliper pistons back into the body and check that fluid is able to return to the reservoir. If it is set too long, fluid is prevented from returning to the reservoir and the brake will gradually seize on as the fluid warms up in service and squeezes the pads onto the disc. When doing this, remove the cap and diaphragm and observe the fluid returning. You might have to align the caliper so the bleed nipple is uppermost as this will allow any air trapped to be bled.
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I did this mod a while ago. Reading the instructions I believe it refers to the port position in the body of the master cylinder may be being masked by the adjustable plunger. Move the plunger in and out and keep on pumping until you see the bubbles diminish and the lever getting less spongy and "solid" indicating that all air has been evacuated from the system.