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Rear brake locking

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So it startedlast year. It locked up on the trail. So i cleaned the master cylinder and changed my piston seals. It worked fine for a ride or two then i parked it for the winter. I noticed over winter i lost fluid and brakes kept going getting stiff. Went for a ride down my road to test it out and it stuck again after.i took it aprs anfpd found a little bit of gunk in the master cylinder (nothing really that should cause problems but ) after putting it back together went for a little ride and worked perfict. Havnt rode it since and its stiff and lockes up when i run it. I thought it might have been my warped roater, but once it worked fine for a ride. So know i dont know what do to

1999 rm125

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Is your wheel out of whack?

Are your rear wheel position lock nuts even on both sides?

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You didn't accidentally put DOT 5 fluid in it, did you?

or DOT 3

 

dot 4 is what you want.

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or DOT 3

 

dot 4 is what you want.

 

 

As far as the context of this discussion (brakes locking up and sticking) DOT 3 won't hurt anything, it just boils at a lower temperature. DOT 5 (not to be confused with DOT 5.1 ) on the other hand is completely incompatible with the seals in any brake system that uses DOT 3 or DOT 4 fluid. It will cause the seals to swell and stick.

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I used out dot 3 in way back when it first got messed uo. Then noticed right it wast right. So its dot 4, besides dot 3 can go in a dot 4 system but not the othe war round. And my tire is level. I just changed my tires, im an auto tech so im no newb but i cant figure it out

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I used out dot 3 in way back when it first got messed uo. Then noticed right it wast right. So its dot 4, besides dot 3 can go in a dot 4 system but not the othe war round. And my tire is level. I just changed my tires, im an auto tech so im no newb but i cant figure it out

 

ok well i just know dot 4 only.

 

not disrespecting your credibility as an auto tech but everyone does make mistakes.

 

give it a look because i have worked in a shop as well as seen MMI master tech ( My Grandfather) &%$#@! up the alignment and its worth a look.

 

if your rotor is fine, you sprocket is fine, your aligned. your Master C. is cleaned your brake lines are in working order and arent trash, your brake is working properly. i dont know. i just wanted to try and help as best i could. without a bit more information or maybe a picture im out

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If you're losing fluid, a seal is bad. If a seal is bad and fluid can leak out, moisture WILL get in (brake fluid is hygroscopic) and cause corrosion to the pistons and deteriorate the seals. You need to rebuild the caliper and master cylinder, and completely flush the system of all old fluid.

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You need to  thoroughly clean, and rebuild the master. Clean the line, disassemble the caliper, and clean it too

Edited by 717 MOTORSPORTS
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Its all new fluid and i cant find were the fluid could have leaked from. I just noticed the low fluid. And i thought rotor at first but after cleaning the MC it worked fine. Then i didnt use it for a week and got stiff

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If you're losing fluid, a seal is bad. If a seal is bad and fluid can leak out, moisture WILL get in (brake fluid is hygroscopic) and cause corrosion to the pistons and deteriorate the seals. You need to rebuild the caliper and master cylinder, and completely flush the system of all old fluid.

Agree this is the only way to completely fix the problem. 

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Pulling the calipers apart and cleaning thoroughly then popping in new seals is not a difficult or expensive job.  Same with the MC.  You can do it all in a couple hours.  Best way I found to clean the pistons is to use rubber electric tape to build up a small grinding stone so you can mount the piston on the stone and spin it with a drill.  I started with WD-40 and Scotch-Brite and then went progressively from 800 to  3000 sandpaper.  Probably overkill, but they looked new and worked like new, too.  

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I would look at adjustment. Ran into it many times. If the piston on the master isn't clearing the reservoir port your brake pressure will build and lock the brake.

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I cleand the MC with a brake clean and a tooth bruch and the caliper has all new seals. But what adjustment? i know theres one to adjust the pedal how far you go push down. Right now its adjusted all the way down so i can get the MC to be open all the way and be sure its closing

*get full motion/pump

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Hey Kodey! What part of rebuild the master, caliper, and clean the system do you not understand??? By the time you keep reading,typing, and trying all these half assed solutions, you could have had the repair done properly

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What part of i have and the problem keeps coming back do you not understand. Ive cleaned it more then once and they still stick. Now im low on fluid and dont have the means of getting more right now. So im looking to find anything that could help.

Ive read somewhere that the inside of the line could get old and the lining could fall off and act like a check valve? Any thoughts,

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Ive read somewhere that the inside of the line could get old and the lining could fall off and act like a check valve? Any thoughts,

 

 

I've seen that happen on old high-mileage cars. Never saw it on a bike, but I suppose anything is possible.

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