No rear brake pressure

[Noobi06]

I cant seem to get any pressure in my rear brake on my EC 125 2005.
The bike was bought in parts so the rear brake wasnt in the best condition. Ive rebuilt the master cylinder, not the slave. I reverse bleeded and everything but I cant get any pressure

 

[gasgasman]

The brake hose can delaminate internally, preventing fluid flow.

 

[(F5)]

That is fairly preposterous. I've never seen a tube failure.
Until I did. Ohh. So yeah, worth checking.

I've tipped bikes up to try make caliper at very bottom. 300s are easy but not sure of 125 setup.

Actually that's not 100% true. 300 was easy. Until it was not. Was an odd size, like 1/2". I couldn't find a similar mc.

In the end I sent it to a crowd that relined it with a steel sleeve. No problem thereafter.
The ally bore wears pear shape. A new seal leaks 50% of the travel.

 

[Noobi06]

If it helps, fluid comes out of the nipple so it cant be the hose right?
Feels like the piston seal is the only possible thing
By the way I am using dot 5.1, not dot 4 but that shouldnt make a difference Im pretty sure of

 

[SS109]

Have you tested to see if the MC is putting out pressure?

 

[Noobi06]

Im sorry but I dont quite understand what you mean by that. What does it mean and how do I test it? Thank you

 

[SS109]

Sorry, I forget that not everyone is a tool freak like me. I know it's not common for most to have but a hydraulic pressure gauge that you can bolt on to the output of the MC, or at the caliper, that allows you to see what pressure it makes and if it holds that pressure. There is always some bleed down but pressure shouldn't drop fast enough that you can see it easily.

 

[Noobi06]

Oh okey, well no I have not got one. Right now I am really confused to why its not getting ?ressure. I really want to fix it so I can get inspection done and ride it during summer

 

[(F5)]

So. You state that it must be the rear piston.

Closed minded thinking right there.

It Could be. But never Must.

If the tiniest corner could harbour a pocket of air, you will never bleed it. That's why I try reposition the caliper relative to the cylinder..that worked on several race bikes with hybrid brakes. European bikes may be susceptible.

Until I fould the cylinder was not working correctly.

 

[Noobi06]

sd

Okey. Do you recon I should have the caliper at the bottom and put the cylinder above it, that way the fluid goes down into the caliper, like gravity? I attached an image showing what I mean.

 

[(F5)]

Other way. Airbubbles rise and hide out in crevices above caliper bleed nipple. I've also taken calipers off and squeeze with clamps to force liquid towards master, hopefully flushing any bubbles with it.
I bleed the hose banjos as well if they have a nasty loop. Rag over banjo, press lever, crack bolt open and close. Release lever.

 

[Noobi06]

I will try. Thank you!

 

[Noobi06]

I have tried bleeding evey way. I have rebuild the master cylinder. I have checked it twice if anything was wrong. I have a new brake line. I cannot get it to work. Dot 5.1 oil (should be dot4 but its the same). Im gonna give up. I cant do this anymore. What the fuck is wrong

 

[webmaster]

Makes me thing of something I read from the late Jim Snell (RIP). If the master cylinder adjuster is adjusted out too far it will block the bleed hole and it won't replenish the system from the reservoir. I would make sure the adjustment at the master cylinder/brake pedal is "middle of the range" - to ensure this isn't the case.

Just something to check.

Also, I have a motive vacuum bleeder. Pulls through the system from the bleeder at the rear brake. Have you tried one of these?

Note that, given Jim Snell's comment above - if you pull the brake system off and "hang it" to get it to bleed out, then you need to have the master cylinder plunger in a good position so that the bleed hold in the piston is free and open.

jeff

 

[(F5)]

Actually, I've seen that. My Beta Rev3 I needed to take the lever off to work that out.

 

[Noobi06]

Finally finally finally works. Was actually about to quit everthing and just give up. Just going to fix some minor things now and pass inspection. After that im putting fresh plastics, a number plate instead of headlight and a pair of bolt on chrome supermoto wheels! Will be nice alongside with a new engine and rebuild suspension and everything else