master cylinder ????????

[kwackkev22]

hi all just a question about the pump part of the master cylinder does the alloy part with the rubber seals do any thing to compress the brake fluid i know the rubber seals obviously compress it but if the alloy part is slightly worn would this effect the leaver pumping up iam having real problems bleeding the front brakes up on a zx9r ive emptied the fluid 5 times now and put ptfe tape on the bleed nipples and all the bolts are tight did look at the master cylinder and found the ally part worn slightly just wonderd if a rebuild kit would help gettin the leaver hard again
thnks kev

[Greeboid]

My limited understanding of brake fluid makes me think it doesn't compress under pressure at all (unless it is contaminated with water.... or air).
As to the bleeding problem... older 4 pot kwak brakes can be difficult to bleed. Why not try a garage! it may not be as expensive as you think.

My problem is slightly more complex. I just bought an L9 bike from what I now consider to be a dodgy little shop in Poole.
I have now discovered it has a front brake disk from a breakers, a wiring loom that's been patched up more than Joan Rivers and lots of other problems.
The brakes were spongy but I bought it anyway even after they took it out back of the shop and bled it again.... I guess I was blinded to its faults because I have always wanted one.
Can I bleed it? can I b "e" g g e r! Back brake no problem, but I can still pull the lever back to the bar after putting about a litre of fluid through the front.
I thought it might be the hoses so I put Goodridge stainless hoses on it. Nope.
I dismantled the master cylinder and found a nick in one of the seals. AHA!
Bought a kit for the L6-L9 which arrived today. (Interestingly it will also fit, of all things, a Yamaha TDR125).
But I have my doubts about my bike though, as it would seem that it has an (L5 or older) brake master cylinder. What the microfiche doesn't show is that the early L models had exactly the same cylinder as H models. They changed it for what appears to be a smaller bore at L6.
So I have a question:
Will the seals from the new kit fit my piston?
Somehow I doubt it but, watch this space, I find out tomorrow.

[masterofinsanity]

i've just rebuilt Gems master cylinder with new piston/seals and spring and it made feck all difference.

[Greeboid]

How did you get on? Is it sorted?
I have fitted a new Brake Master Cylinder and coupled with Goodridge hoses they are still spongy-ish but a hell of an improvement.
If you did get it sorted it would be great if you have any bleeding tips. (That's tips on bleeding, not to be read in the coarse vernacular).

The dodgy little shop in Poole also left a rotting foam filter in the airbox. Some pre-delivery check! Replaced this with a K&N but now need to strip the carbs to get the rotting foam out of my float bowls.

A big learning experience this is turning out to be. Don't buy a ZXR400 because they are desireable. Not everyone has looked after theirs.

[zimm]

our ZX4 had a bit of excessive lever travel (its got zxr H2 brakes, goodridge braided hoses and EBC HH pads)) today, so i whipped the calipers off, pumped the lever till the two pistons on whichever side moved first extended fully (left pads in so they didnt pop out) wiped round the pistons with a cotton bud soaked in WD40, lever'd them back home, did the same to the other side, and then repeated the process on the other caliper.

job done, no more "lever to the bar" and nice and firm.

what happens is that the pistons get used to being in one place, and stay there so when the pads are worn a bit the pistons have miles to travel before the pad contacts the disc, this translates as excessive lever travel (which feels spongy, because as the pistons extend the ratio between lever movement and piston movement changes due to the pivoting design of the lever), cleaning them up, then pumping them up lets the pistons sit at the correct distance from the discs and its all good again.

[zxr_oli]

our ZX4 had a bit of excessive lever travel (its got zxr H2 brakes, goodridge braided hoses and EBC HH pads)) today, so i whipped the calipers off, pumped the lever till the two pistons on whichever side moved first extended fully (left pads in so they didnt pop out) wiped round the pistons with a cotton bud soaked in WD40, lever'd them back home, did the same to the other side, and then repeated the process on the other caliper.

job done, no more "lever to the bar" and nice and firm.

what happens is that the pistons get used to being in one place, and stay there so when the pads are worn a bit the pistons have miles to travel before the pad contacts the disc, this translates as excessive lever travel (which feels spongy, because as the pistons extend the ratio between lever movement and piston movement changes due to the pivoting design of the lever), cleaning them up, then pumping them up lets the pistons sit at the correct distance from the discs and its all good again.

Just did that to my brakes, it's amazing!
Now bites just after the click of the switch, rather than about 1cm away from the handle bar.

[Gemini]

may have a go at that, also thinkin about coating the piston in rubber grease then putting back together

gem

[kwackkev22]

i got it sorted to hes standards he was happy when he took it away but i wasnt happy with the leaver travel . There just a pain in the ass to bleed.I did the single caliper with single brake line on my mito in 20 mins tops and the leaver was rock hard. So its the fact that these double caliper systems are the pain. I did put the new master cylinder on this bike and it made sod all difference. As for tips on bleeding them theres ptfe tape on the bleed nips (plumbers tape) and i modified my mity vac pump to suck of both calipers with some clear pipe from bnq and some 3 pointed pipe connections. One end in to the pump its self and one length of pipe to each caliper i could have both bleed valves open at the same time and could empty the brake res at least 2 and a half times with out having to reset the pump.If you have braided lines as well i was told that the lines in side are really thin so its easy for air to get trapped so tapping flicking the lines can help thats my 2ps worth lol you just have to stick with it bleeding brakes is both hard and boring thats my finding
kev
thanks for all your help and input

[masterofinsanity]

don't think its the case of twin pots cos my gix has twin pots and they are fantastic brakes, i think its just kawasaki brakes mate they always have been shite!

[kwackkev22]

oh i mean in beeding terms theres more room for air to get traped. i back beld the brakes on my mito and it just pushed all the air stright out the res at the top. where if you try that on a double line system chances are you would push the air in to the other caliper :smt013