Rear Brake Master Cylinder Fault

[ByJupiter]

Hello all!

(My Bike = 2003 single spark gs)

An hour or so ago I got my gear on to go out for a spin... started to move the bike off the centrestand and then noticed that she was hard to move once off the centrestand. (Felt like the rear brake was on).

So, I started to have a look around and found that the rear brake pedal had no resistance - then saw that the rubber part on the lower section of the master brake cylinder was flapping about and the thin rod which goes through the rubber is very loose & wobbling around. Have I lost a part perhaps, is it an easy fix or do I need to shell out on a new rmbc?

Grateful for any advice as always,

thanks in advance.,

Joops.

[Ian Porter]

I've just replaced my rear master cylinder today as it happens.

dead easy to do on the Funduro.

the plunger in the Master Cylinder usually gets to a point to where it doesn't return and leaves the actuator rod loose and the rear brake pressurised. if you undo the blead nipple on the rear calliper I bet the brake frees off.

I think Motorworks 'may' do a service kit but I couldn't get mine apart and a replacement was £40 (inc delivery) from Intobikes, and came next day.

I took the opportunity to clean the back calliper and fit new pads at the same time.

just got to take it for a test ride now

Ian

[ByJupiter]

Hi Ian:

Thanks for the advice,...I guess I'd better play it safe and splash out on a new mc like you suggest - handy things are brakes, so worth me keeping them in good nick!

40 quid ain't so bad, I thought it might be a frightening amount - thanks again, I'm most grateful.

TTFN,

Steve.

[PaulEngland]

I did mine last year, as Ian said not a hard job to do...

[ByJupiter]

Hi Lads:

Thanks again. Do you happen to know which is the correct one to get? I've seen the link (above) that Ian very kindly referred to, but being a bit of a duffer, I'm not 100% sure which is the right one for my 2003 f650gs (single spark - f for "fumper")

Thanks again, much appreciated,..

Steve.

[PaulEngland]

Is this the one you want!

Part number (10477660) with the link that Ian provided

[ByJupiter]

Hi Paul & Ian:

Many, many thanks chaps, I'll get onto it in the morning and will order one up!

Thanks for your patience and help. If you venture up to the Isle of Skye anytime, the beers are on me!

TTFN,

Steve

[Ton]

What happens to the master cylinder is that water gets past the rubber and it creates corrosion in the cylinder. And when the pads wear down it eventually gets to the part where corrosion is and it gets stuck. So if you push the piston back in you will see the corrosion. If you replace the pads the piston will have moved away from the corroded part already very often. And if you don't change brake fluid frequently you will also get rust inside the cylinder and in that case I would always renew it. The rust behind the rubber seal can be cleaned up and if you put some brake grease underneath the rubber sometimes you can keep this corrosion away. That is also a reason why I am not a fan of jetsprays. Good luck with replacing it. It should be a very easy job.

Ton

[ByJupiter]

Thanks Ton, that makes a lot of sense. Since having bought the bike in September, she has been outside in my back yard with only a bike cover for protection. I'm going to build a shed for her during the months ahead so's to avoid her being exposed so much to the elements next winter.

I'm on to ordering the part now. Will let you know how I get on.

Thanks again for the helpful info.

TTFN,

Steve,

[PaulEngland]

What Ton said about putting grease in the rubber shroud is a good idea this should keep the moisture out a bit...

A water resistant grease...

Not sure if a Petroleum jelly like vaseline would work or react with the rubber, not sure?