Brakes

[636steve]

Ok so I have replaced the seals in the front calipers on my track bike (GSXR750 k5) as I had a couple of stuck pistons.

I have now been trying to bleed the brakes and getting no where. Lever comes all the way back to the bar and just about manages to slow the front when pulled.

I have tried the following:
bleeding by filling the reservoir up and using a one way valve and pumping lever (always worked in the past) - no pressure
vacuum pump to pull the fluid through - no pressure
pushing fluid up with a syringe from the bottom - no pressure
cable tying the lever overnight - no pressure

I am now beginning to wonder if it is a problem with the master cylinder. The brakes worked before I started although have always been a bit spongy. The master cylinder was changed under a recall about 3 years ago and has probably done about 9 track days since. I have read that draining the system can cause problems with the piston moving further back than normal and causing problems. Don't know if this is the case.

I have removed the brake lines from the master cylinder and when I put my finger over the hole and pull the lever I get a bit of pressure but not a lot and if I pull in the lever and cover the hole there is a bit of suction but again not a lot. I am not sure how much pressure there should be.

Sorry for long post but thought I would include everything.

Anybody got any sensible suggestions?

[MOzZereLLa]

Is there a seal inside the master cylinder? Could that be leaking?

[636steve]

Not sure, you can buy a rebuild kit for it so I assume there is a seal of some sort.
Might just take it apart and have a look.

[Tiiimmmaaayyyy]

Didn't some of the K model GSXRs have a recall for the master cylinder?

EDIT: http://www.visordown.com/news/general/massive-worldwide-gsx-r-recall

Might be worth getting it done if not done already

[636steve]

The master cylinder was changed under a recall about 3 years ago and has probably done about 9 track days since.

See above

[Tiiimmmaaayyyy]

The master cylinder was changed under a recall about 3 years ago and has probably done about 9 track days since.

See above

See, I was right

[Green_Ninja]

It the master cylinder a radial one? If so there should be a bleed nipple on this.

I would suspect the MC seals as well so as you have the brakes apart get e seal kit and clean and rebuild the M/C.

Start bleeding by making sure all the caliper pistons are pushed all the way back into the calipers and use something to hold them in place.

Get a large syringe, fill with new brake fluid, use this with a short piece of bleed tube to push fluid up the system from the caliper to the M/C don't rush take it slowly. Assuming it is a radial M/C then one you have fluid through the system crack off the nipple on the M/C and gently pump the brake lever to expel any air trapped in the top of the system. Now bleed the system as normal but make sure the caliper pistons stay fully 'in' the caliper. Once you have no air coming through, one caliper at a time slowly pump the caliper pistons out until they make contact with the brake pads, continue to bleed until you have a good solid lever, Then do the other one.

Hopefully that should do it. DO NOT TRY TO RUSH IT.

Good luck
   

[Dom1]

Also try turning the bars so that the reservoir is at the highest point then wiggle the brake lever through the first 8th of its travel.

I was amazed how much air this got out of mine, although mine is currently a DR350 so brakes are a relative subject.

[Andy M]

Get a large syringe, fill with new brake fluid, use this with a short piece of bleed tube to push fluid up the system from the caliper to the M/C don't rush take it slowly. Assuming it is a radial M/C then one you have fluid through the system crack off the nipple on the M/C and gently pump the brake lever to expel any air trapped in the top of the system. Now bleed the system as normal but make sure the caliper pistons stay fully 'in' the caliper. Once you have no air coming through, one caliper at a time slowly pump the caliper pistons out until they make contact with the brake pads, continue to bleed until you have a good solid lever, Then do the other one.

absolutely this, has worked everytime for me

[636steve]

Sounds like it is the master cylinder playing up then.

Now do I rebuild the existing one or get a blingy new one

[Green_Ninja]

Sounds like it is the master cylinder playing up then.

Now do I rebuild the existing one or get a blingy new one
[/quote

depends on your budget I suppose 

[Dom1]

Bling it up, lets face it, you are not going to trust the one you have again really.

[Green_Ninja]

Bling it up, lets face it, you are not going to trust the one you have again really.

good point well made 

[636steve]

Bling it up, lets face it, you are not going to trust the one you have again really.

Good point.


Ok so what should I go for brembo, accossato or something else?
Also anyone got a simple exlanation of what the ratio number mean i.e 19x20? what is a standard one normally?

[Carbon_ZX6R]

Bling it up, lets face it, you are not going to trust the one you have again really.

Good point.


Ok so what should I go for brembo, accossato or something else?
Also anyone got a simple exlanation of what the ratio number mean i.e 19x20? what is a standard one normally?

is  accossato on par with brembo as I don't know much about them and that's what I have just taken off the b1