master cylinder rebuild!

[andy230]

Hello,

Further to my investigations into the DR front brake, its become apparent that bullet350 was right, and I’m probably going to have to rebuild he master cylinder.

I noticed that initial application of the brake causes a slight raising of the level in the reservoir.

I am presuming that this means that rather than forcing fluid down the line to the calliper, its instead being forced back into the reservoir. 

Make sense?

So having never rebuild a master cylinder before, what am I looking at replacing?  Will go for genuine Suzuki parts I think, unless anyone suggests otherwise??  I have a good Suzuki shop quite local to me

www.spares-direct.co.uk

And how do I start??  Remove the rubber boot to get at a circlip?

Cheers for now, thanks for your help in this saga!  Why are all things I attempt an absolute mission?!?

speak soon

a

[Steve H]

Hello,

Further to my investigations into the DR front brake, its become apparent that bullet350 was right, and I’m probably going to have to rebuild he master cylinder.

I noticed that initial application of the brake causes a slight raising of the level in the reservoir.

I am presuming that this means that rather than forcing fluid down the line to the calliper, its instead being forced back into the reservoir. 

Make sense?

So having never rebuild a master cylinder before, what am I looking at replacing?  Will go for genuine Suzuki parts I think, unless anyone suggests otherwise??  I have a good Suzuki shop quite local to me

www.spares-direct.co.uk

And how do I start??  Remove the rubber boot to get at a circlip?

Cheers for now, thanks for your help in this saga!  Why are all things I attempt an absolute mission?!?

speak soon

a

It depends on how much the level is rising, I would expect some flow back into the reservoir. If you look at the bottom the the reservoir, there should be a small pin sized hole. This is the cut-off hole (I think thats its name) . The purpose of hole is to allow fluid in front of the piston seal, which sits upstream of the hole. Pulling on the lever pushes the piston and seal forward. As the piston moves forward it displaces fluid which comes up through the cut-off hole, after the seal passes the cut-off hole pressure starts to build and the caliper pistons move. So the fluid you are seeing coming back into the reservoir could be normal.
Another test for a duff m/cyl is to apply a constant pull on the lever, if the lever slowly moves back to the bar then fluid is leaking past the seal.
It might also be worth checking the hole is clear as if its blocked it will be a pig to bleed.

[andy230]

...right....

Its not masses of fluid coming back, so maybe ok??  And it feels ok once the brake bites.  Not too spongey, it just takes a lot of movement before anything happens with it, and I'm not cool with that!

Suspect I've been on the Skorp too long!

Time to supermoto??!

a

[Steve H]

Have you tried loosening the caliper yet ?
The other thing I do is hold the handlebar steady and hit the lever ball-end with the palm of my hand, this can often 'shock' air out of the m/cyl into the reservoir.

[andy230]

Have you tried loosening the caliper yet ?

Yes.

I'll try your idea about getting any air moving....

cheers, as ever!

a

[Steve Lake]

I agree 100% with SteveH......I have 4" of clear plastic pipe as a resevoir on my rear break (al la racers)... and you can see the  fluid rise in there....a bit...when the brake applied.....but that particular unit is the best brake in the fleet :-) (god knows why....and not much use on the back)

So , new fluid....and a good bleeding session......it has been said you're a bit of a bleeder Andy....so should be a piece of pi55 :-)

pip pip

[guest146]

Andy

The cut off hole is to let fluid back into the master cylinder when and if the pads/disc expand otherwise the brake would bind when hot and to allow you to bleed the system.The first fraction of movement will make a slight movement to the small fluid chamber after that the bleed hole is blocked off and the movemet puts on the brake.

 The name of the game is to keep it all clean and use either rubber grease or brake fluid. Look very closely at the edge of the seals on the piston for cuts or being rounded off and also the bore of the master cylinder for scoring and if unsure change it.

Regards Ken