Zakalwe Posted December 7, 2008 Report Share Posted December 7, 2008 OK, so I have replaced the caliper seals on the front calipers on the Gixxer track bike. New Goodridges braided lines are on. A Kawasaki ZX-10 master cylinder is doing the pumping duties (the guy I bought it off said it was brand new...I have no reason to doubt himm judging by the condition of it). I have bleed the lines and have a decent brake. I cable-tied the lever back overnight and re-bled the master cylinder again this morning. However, leave it for 30 or so minutes and the lever comes back to the bar. Pump it a couple of times and the brake is good again. It looks like the pistons on one caliper are moving back into the caliper.....almost like their is a partial vacuum in the system. I can see where the pads have moved back from the disc on one side. Any ideas guys, 'cos it is doing my nut in? Link to comment Share on other sites More sharing options...
Liamo Posted December 7, 2008 Report Share Posted December 7, 2008 Are they 6 pots? Link to comment Share on other sites More sharing options...
RealityRSV Posted December 7, 2008 Report Share Posted December 7, 2008 assuming there are no leaks anywhere, i'd have thought your problem lies at the master cylinder. not having stripped one down however... i'm afraid i cant offer further specific advice. i'd start doubting that seller though, at least until you've found where the problem lies. only other scenario i could think of is if the disks are slightly warped, but i'd have thought that would be pretty apparent when you brake. Link to comment Share on other sites More sharing options...
David W Posted December 7, 2008 Report Share Posted December 7, 2008 Sounds to me like something isn't right between the caliper piston and seals, and the seal is acting like a spring and pulling the pistons back into the caliper. It will feel spongy because it's having to take up the gap when you first pull the lever. Link to comment Share on other sites More sharing options...
David W Posted December 7, 2008 Report Share Posted December 7, 2008 Someone might correct me, but I think one of the functions the seals have is to pull the piston back a touch when you release the brake and the pressure drops. If the seal isn't lubricated properly the piston can come back too far. Just an idea? Link to comment Share on other sites More sharing options...
Mr.Pigdog Posted December 7, 2008 Report Share Posted December 7, 2008 Hello mate-try unbolting the caliper with the pads still in position and pull it off the disc just so theres about 1-2 mm of pad contacting the disc.Then give the lever a couple of pumps so that you have to kind of 'wedge' the caliper back on.Those symptoms sound like a binding seal-as you say with the seal retracting the piston too much. Link to comment Share on other sites More sharing options...
lorenzo Posted December 8, 2008 Report Share Posted December 8, 2008 Another nice way of getting that last bit of air out is to pump the pistons more or less fully out once you've done your final bleed. Take the caliper off the discs, and get a dirty great screwdriver or something and push them all the way in, with the bleed nipple open. It's not unknown for air to be lurking within the space behind the piston. Having written all of that, I had exactly the same problem with an 'as new' master cylinder once, and guess what the problem was? I proved it in the end by swapping over to an old master cylinder. Irrespective of its size and design etc, a known working m/c will tell you what you need to know. Link to comment Share on other sites More sharing options...
ronenige Posted December 8, 2008 Report Share Posted December 8, 2008 If the pistons are sticking on the seals , one way around it is to remove your pads , one calliper at a time , pump the pistons a fair way out and assuming your pistons are clean lubricate them with silicone grease , a small paint brush is ideal for this purpose , , the easiest place to get silicone grease is at your local plumb centre or b and q warehouse , a small tube will last you for years , do this once a year to keep your brakes feeling at their best .obviously then push your pistons in gently and refit the pads , if the pistons do not go back in easily , ideally by hand then they are either out of square or there is a problem that needs further investigation Link to comment Share on other sites More sharing options...
David W Posted December 13, 2008 Report Share Posted December 13, 2008 I think discs can be replaced singularly, but I think personally I'd have to buy two. Link to comment Share on other sites More sharing options...
kwakbiker Posted December 13, 2008 Report Share Posted December 13, 2008 Dont forget new pads to go with new discs as well...sorry. Link to comment Share on other sites More sharing options...
Mr.Pigdog Posted December 13, 2008 Report Share Posted December 13, 2008 Yeah i'm with david W-i reckon its best to replace as a pair-guess it's dependant on lots of things:quite often if they warp its either because they're that thin that they need replacing anyways or the dreaded disc lock thing.Are the discs genuine and therefore quite pricey?personally i'm the kind of guy to replace both fork seals if one goes,so it's often down to personal choice.Saying that im not quite sure what the effects of having one thick new disc and one thin old one.i would also like to add i have spent the evening in a pub and have a bellyfull of quite nasty belgian beer.Hey whats the worst can happen if you replace only one disc? Link to comment Share on other sites More sharing options...
Ascalon Posted December 18, 2008 Report Share Posted December 18, 2008 this is also a common problem with older Kawasakis running Tokicos. Even if your discs are true, you can get a situation where you have too much lever travel before full pressure is applied. After owning two ZZ-R400s, a ZZ-R600 and a ZX-6R (with six pots) I have found the best thing to do is red rubber grease (Castrol) on a rebuild and the push out, clean and grease method described above regularly thereafter. As the calipers get older, the seal seats seem to do something odd, and the seals can rock a little as the pistons start to move. This can lead to the exagerated withdrawal of the pistons into the caliper meaning that too much lever travel is then taken up pushing the buggers back out. The red rubber grease is hydraulic seal compatible, so it doesn't bugger things up and ensures a smooth, even slide every time. Good luck, A Link to comment Share on other sites More sharing options...
budda Posted December 18, 2008 Report Share Posted December 18, 2008 I had a snag where there was corrosion behind the seals where they seat causing the seals to grip the pistons. Also if its a radial m/c off one of the later zx10's yer ok but the 04/05 is crap as I had to replace mine with a brembo m/c. Good luck fella. Link to comment Share on other sites More sharing options...
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