Author Topic: Master cylinder swap?  (Read 152 times)

Itsme

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Master cylinder swap?
« on: June 30, 2021, 07:45:45 AM »
Hi all

The front brake lever on the Mighty Midget (GN250) has very little movement or feel and has been quoted on a previous MOT certificate that came with the bike as 'too hard' whatever that means. It is hard to use though due to the lack of travel and the total lack of progressive feel, it is off or on but on has marginal performance.

I intend to check the calliper etc, but have a master cylinder left over from my CBF500 and just wondered if it might be advisable to try a swap. I understand there are considerations of bore size and capacity of the cylinder etc, but feel it might be worth a try.

Failing that there are GN250 specific master cylinders on ebay (Chinese) for £12.99 would one of those be a better bet?

I look forward to your wisdom gents.

Spartacus

iansoady

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Re: Master cylinder swap?
« Reply #1 on: June 30, 2021, 09:40:33 AM »
The bore of the cylinder does make a big difference to feel. Have you tried other similar bikes / is there anyone here who could say whether the "woodenness" is normal?

I changed the front brake master cylinder on my Guzzi for a 13mm bore one from a Honda Silverwing and it gave a much nicer feel. The brake still wasn't that good however.....

I'd probably steer clear of the ebay ones for my braking system.

This might help: http://ducatimeccanica.com/brake_ratios.html
Ian.
1952 Norton ES2
2008 Yamaha 250 X-Max

Itsme

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Re: Master cylinder swap?
« Reply #2 on: July 01, 2021, 05:11:25 AM »
Thank you Ian for a very considered reply and a very interesting article. I gave the calliper a good clean, bled through new fluid and shaved a very small amount off the heel of the brake lever where it presses on the end of the piston and that has improved things a little. I have also ordered some new pads as a different compound might help too so I think rather than get all experimental I will stick to these small gains.

On reflection I also think I agree with not buying a Chinese replacement!

Spartacus