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Front Brakes Locking Up

30K views 24 replies 14 participants last post by  genetuck 
#1 ·
A few weeks ago I went to a track day in TX. While doing my warmup laps my front brakes began to drag and no matter how much throttle I applied it became clear I was stopping now. Luckily I was able to get out of the main line and stop safely. I also noticed that my brake lever was insanely stiff to where I couldn't squeeze it at all. I thought the reservoir was overfilled and as the brakes were heating up the fluid didn't have enough room to expand so I drained some out of the system. So I went back out and in one lap the same thing happened. I get back to the pits and cracked the bleed screw on the master cylinder and immediately the bike was free to roll.

I figured the problem was in the master cylinder and not allowing fluid to flow back up the lines. I ordered all new internals for the master cylinder, completely disasembled my brake system to blow out the lines. However, just dragging my brakes around the neighborhood I could get them to do the exact same thing. Brakes lock up and the lever get too stiff to squeeze. So I figured it must not be in the master cylinder but rather the calipers. I took the calipers off, bought new seals and rubber parts, and had my local shop rebuild them for me. Now this weekend I put everything back together and after quite a bit of work I was able to get the caliper pistons to finally move out against the pads. I've vacum bled the system, gravity bled it a few times, and left the brake lever ziptied against the bar over night. I do have brakes now but they are very weak. They will stop the bike, but I almost have to squeeze the lever to the bar and even then it doesn't try and crush my nutz like it should. During this process I also upgraded to shorty gold pazo levers and have them adjusted all the way out.

So please help me guys. I've searched the forum here a lot and found a few cases of people's bikes doing the EXACT same thing, and saw they had pretty much done the trouble shooting just like I have and thrown the same replacement parts at the bike, but never heard how the stories finished and what the exact problem is. Is the master cylinder somehow junk even though I replaced the internals? That seem to be one thought someone posted a while ago. Anyways I'm starting a new thread to get some new feedback and hopefully get a solution figured out. I'd also like to document the solution so that future owners can find an answer here.
 
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#3 ·
No I didn't get the new levers in time for the track day, the whole locking up thing was with stock levers, just SS brake lines that I had been running for a year.

When I put the calipers on after the shop rebuilt them the pistons were bottomed out in each caliper and using the lever I never could get them to press out against the brake pads. I saw in the forum here where someone suggested pulling the lever off and using a tool to manipulate the piston manually. I did that and it worked but getting that last little bit took/is taking forever. Last night with the braking power I have I really worked the brakes. I got the rotors so hot the heat almost instantly burned my hands while touching them with my gloves on. So maybe I fixed the over heating problem, but the brakes are still way too soft and squishy. I've been feeling that my brakes were getting weak on me for almost two years, so I upgraded to the SS lines, and currently have HH pads on. Still have never been impressed with the braking power.
 
#5 ·
I didn't have to pry the pistons out. They finally moved out when I manually manipulated the master cylinder piston. It's like the lever isn't letting the piston make a full pump, but it's not the lever I get a lot of range of motion, I think more than I did with the old lever. The master cylinder just doesn't pump very hard.

I'm thinking of taking it back into the shop and letting them figure out. Part of me just wants to ride now that it's finally stopped raining, and we're talking about my brakes here I can't afford to play around with a brake system that isn't functioning. It's just frustrating because it's such a simple mechanical system.
 
#7 ·
i experienced this and have the exact same problem. i made a thread about this last year. to this day my front brakes have never really felt as tight. i normally use 1 finger to brake and after the incident i had compensate and use more effort so now i'm back to using 2 fingers. i have a more positive feel in the rear brake.

before i went down the brakes were bled and there was dark fluid coming out. i think that had something to do with locking up the lever. where does that dark fluid come from?
 
#8 ·
i have the same problem before, I rebuilt my front calipers with new rubber seal, packing and wiper and the brakes didnt lock up on me anymore BUT when i pull my levers, its very soft but i can still brake, its not as strong, i changed my lines to new ones and it didnt solve my problem. So i went ahead and replaced the PISTON-COMP-BRAKE No. 43020 on the diagram on picture attached. since then, my brakes feels so strong.
 

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#9 ·
That's exactly where I'm at except I first replaced the piston-comp-brake, and the brakes still locked up on me, so then I had the calipers rebuilt. Now they aren't locking up but the brakes are way too squishy and weak. It's kind of sad that so many of us have had the exact same issue with the brakes.

Right now I'm debating between taking my bike to the shop to let someone else deal with, or just flat out replacing the entire master cylinder assembly.
 
#12 ·
FELLAS....ok heres what you need to do....mines finally fix after a few parts.....
you need to take the whole brake system apart....open your MC and check if theres any rubbing marks in it...IT NEEDS TO BE SMOOTH...open it and youll see what im talking about....IF THERES SOME RUBBING MARKS>>REPLACE ASAP........then open up your calipers and replace the piston seals and dust wiper>>REPLACE WITH NEW ONES...then make sure your lines are in good condition...clean it with brake fluid or air hose...DO NOT CLEAN IT WITH WATER or BLOW ON IT USING your mouth......whe everything is clean and dry put everything back together....BUY A NEW BOTTLE OF BRAKE FLUID then bleed...trust me this is how i fix mine and GOOD LUCK FELLAS....

i replaced mine with brembo rcs19 which cost me at least $350
Seals i think $60...i dont remember.......GOOD LUCK GOOD LUCK GOOD LUCK
 
#13 ·
I can finally put this story to bed. I'm pretty sure all of the problem was in the stock master cylinder. However, after reading on here about the Nissin calipers being a significant upgrade over the stock set, I decided to do a little looking on ebay. I found a complete front brake system from an 08 ninja for $150. Yesterday that came in the mail, the system was still totally sealed and had just been unbolted from from the bike. I was happy I didn't have to worry about anything sitting dry. I quickly bolted the Nissin calipers on and swapped out my old master cylinder with the 08 model. I'm still running my SS lines made for the 05 calipers so there is bit of slack in the lines, not ideal but not a problem. The brakes finally feel great again. If I was a better person I would put the old calipers on to confirm that it was my master cylinder that was failing, but I'm too lazy to go through all the bleeding again. The new Nissin calipers do feel powerful, but I can't yet say if they are an upgrade yet as I've had terrible brakes for long.
 
#18 ·
I can finally put this story to bed. I'm pretty sure all of the problem was in the stock master cylinder. However, after reading on here about the Nissin calipers being a significant upgrade over the stock set, I decided to do a little looking on ebay. I found a complete front brake system from an 08 ninja for $150. Yesterday that came in the mail, the system was still totally sealed and had just been unbolted from from the bike. I was happy I didn't have to worry about anything sitting dry. I quickly bolted the Nissin calipers on and swapped out my old master cylinder with the 08 model. I'm still running my SS lines made for the 05 calipers so there is bit of slack in the lines, not ideal but not a problem. The brakes finally feel great again. If I was a better person I would put the old calipers on to confirm that it was my master cylinder that was failing, but I'm too lazy to go through all the bleeding again. The new Nissin calipers do feel powerful, but I can't yet say if they are an upgrade yet as I've had terrible brakes for long.

How are you using the 08 mc on your 05? did you change to a 08 lever?
 
#14 ·
Good to hear Merc.. I will get my MC tomorrow. I am definitely sure it is the MC I am having difficulty with.

As mentioned in my previous posts.. I was just hard to believe it was my MC because it was goofy right when I did the caliper swap..

But now that I think about it my lever was not as firm 3 weeks prior right after a recent flush.

Be very careful when bleeding your mc guys.. because the proper way is to use a pressure flush from the reservoir and opening up all the bleeders from the top down..

I believe pumping the MC too many times to try and flush it somehow F up the MC..
 
#15 ·
Brakes locking up?%$%)(*((*^

The issue you had was caused from the lever not being allowed to return all the way to zero braking force being applied. The lever prob. contacted the aftermarket line banjo at the mc and was very slightly bent. I unfortunately have experience with this issue. Unfortunately even after finding and fixing the lever damage on my 06 zx6r the brakes never worked 100% compared to as factory delivered. I believe a flaw in caliper design prevents or makes proper bleeding very difficult to obtain. Just ordered the zx14 set up from Canada, very much looking forward re-joining the world of adequate stopping!
 
#17 ·
Just ordered the zx14 set up from Canada, very much looking forward re-joining the world of adequate stopping!
I think you'll find the Nissin calipers more than adequate, I finally feel like I could do a stoppie again if I had the balls haha.
 
#23 ·
there is a problem with the pistons within the front brakes, sometimes they get too stiff and don't move.
1. remove the screws to open the front brakes
2. open it all the way
3. remove calipers and brake pads.
4. go to work on the piston blocks remove them with pliers and scrape them with sandpaper.
5. also scrape the piston container.
6. bleed the brakes and u might be good to go.
 
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