Hey everyone, Looking to see if anyone here had this happen to them and know how to remediate it(other than "bleed the brakes"). When I first use the brakes after cleaning the pistons(or anytime I move the pistons in or out for any reason, like front wheel changes, caliper cleaning, etc) the bite/pressure build up/engagement point is right there, almost no lever travel. However, over time(sometimes over 2 trackdays(if it's hotter outside), sometimes 4 trackdays) the bite point moves closer to the bar, brakes are still FIRM/work them same, but the bite point moved(about 1/2"). And once it reached that point then it doesn't change any further. The travel distance stays the same no matter the temperature or whether bike is moving or not. Brakes are NOT squishy! Cannot be pumped up. Best I can come up with is that the seals are getting stuck to the pistons and pulling the pistons in too far, but soon as I move them - that position is reset and the cycle starts over. Is this a seal and/or caliper design issue? Calipers are nissin monoblocks from a 2019 zx6r that I got pretty much with no miles on them, it's been doing that from day 1. I fully disassemble, clean and lube the calipers every 10 days or so and clean the pistons(without removing) every couple events(vesrah's are dusty). I tried using brake fluid as assembly lube and tried using caliper rubber grease - no difference. Different rotors didn't make a difference either. Thoughts or ideas?
Bleed the brakes. I know you don't want to hear that but I think it's common to rebleed after multiple track days or races. What brake fluid are you running? I have to rebleed my racebike after each weekend and sometimes during the weekend if I do alot of heavy braking. The fluid will get hot and start to boil which creates air bubbles and that is the feeling of compressed air in the lever. You hinted it happens more often if it's hotter outside. This helps boil the fluid faster. If I am wrong about this then you are not the only one who has to rebleed brakes often. It could be a minor air leak in the system or maybe the seals in your calipers but I have always dealt with this. I think this is more common then you think. I'm on a stock M/C with RBF600 fluid, steel lines, Vesrah pads, and deal with this too. We all deal with this on the race team. Brake fade is real and is why they make adjusters to move your lever further or closer to the bar.
I'm not discounting the possibility of air in the system, but I tried bleeding them when the travel increases - I wouldn't get any air and no improvement in lever travel. Motul 5.1 It just doesn't feel like air in the system(but it's possible I just don't know what that feels like(no sarcasm)). Lever is always firm once engaged. The reason why I'm leaning towards not being air in the system is that if there was air in the system, then why is that when I barely push the pistons in during the front tire change - the lever returns to normal? Maybe like you said - maybe it's normal...
If everything is good mechanically I would bet there's moisture/contamination in the system from either too much time on the brake fluid or from new brake fluid that wasn't up to normal spec. So to fix all of the variables, clean the whole system, check all of the seals, and spend extra time filling and bleeding the new fluid! And always add fluid from an unsealed bottle.
I agree with that, however wouldn't that happen soon as I get rolling, instead of days? Also at standstill, since the rotor isn't moving, it should pump up and feel normal, right? but it doesn't...
Brain fart and yes! When I used to sell chemicals at Tucker Rocky I did run into new brake fluid bottles that weren't sealed correctly at the factory so moisture did ruin the product
so i had this issue all season and it took a while to figure out my issue. i rebuild two sets of calipers and masters. lever kept getting soft. i zip tied the brake lever overnight to see if there was fluid leaking out, which would cause air to come in. turns out my OEM bleeders went bad. i kept seeing fluid seeping out by the threads and this was after torquing them to spec (yea there is a torque spec for bleeder screws). once i put new OEM bleeders in and zip tied the lever overnight again, no fluid was found! now my lever is consistent again.
Was this on a GSXR or another model? Usually on street bikes the bleeder screws rarely get touched... on track/race bikes they seem to be a wear item.
Old news, I know, but the gsxr also had a strange condition with the MC where gas would be produced through some sort of chemical reaction in the piston/bore. doesn't sound like what's happening here since he states simply changing front tires and pushing the pistons solves the problem for a while... 1 / 7 Service Bulletin SUZUKI MOTOR OF AMERICA, INC. 3251 E. Imperial Hwy, Brea CA 92821 USA MOTORCYCLE DIVISION GS/GSX/GSX-R NO. 228 DATE: 10/28/2013 SUBJECT: SAfETY RECALL CAMpAIGN — fRONT BRAKE MASTER CYLINDER MODELS: 2004-2013 GSX-R600 2004-2013 GSX-R750 2005-2013 GSX-R1000 This notice is sent to you in accordance with the requirements of the National Traffic and Motor Vehicle Safety Act. Suzuki Motor Corporation has decided that a defect which relates to motor vehicle safety exists in certain 2004-2013 model Suzuki motorcycles listed above. What is the problem? After a long-term service life of the motorcycle without changing the brake fluid, the brake fluid can deteriorate and absorb moisture. The brake piston inside the front brake master cylinder of some motorcycles may not have uniform surface treatment. This combination of conditions can lead to corrosion of the brake piston. Corrosion of the brake piston generates gas, which may not be adequately purged from the master cylinder due to the side position location of the reservoir port. Gas remaining in the master cylinder can affect braking power by reducing proper fluid pressure transmission to the front brake. Over time, as gas continues to slowly accumulate above the reservoir port, the front brake lever may develop a “spongy” feel and stopping distances may be extended, increasing the risk of a crash.
The stock master on mine is also a nissin but it's the newer style, the one with the reservoir port at the top, thank you tho!
I wouldn't say my lever was getting soft, but I'll give it a shot - it's easy enough to try. Thanks Jim!
just re-read your issue. if the lever is still the same stiffness but less brake bite, have you changed brake pad brands a few times? have you scuffed up the rotors? i'm wondering if the rotors are glazed a bit. how worn are your pads? also, you want to be on RBF600. use the 5.1 for a street bike.
Same stiffness, same bite, but different engagement point. Same pad compound all year, still have 3mm of pad material on them(3.8mm when new)
Maybe check rotor run out. I know you said it happened after rotor change. Maybe the wheels mounting surface is warped? If not, I'd replace the MC. even the replacement was just not best quality...