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Brakes won’t bleed

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Farmingstock
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PostPosted: 22:39 - 23 Jan 2022    Post subject: Brakes won’t bleed Reply with quote

The bike had been stood for a while so I decided to change the fluid before MOTing the bike (Rieju 50cc) rear brake

I’ve tried every which way to bleed the brakes and it’s not happening.

There is no fluid in the system, I have tried the following:

Filled the res up tried bleeding but it doesn’t seam to move from the res as the level isn’t going down.

Used a vacuum pump but it doesn’t suck anything through

Tried reverse filling but ended up with fluid everywhere when the pressure blew the pipe off

Tried bleeding for a good few hours with no joy

Taken off the MS seals are fine and build pressure

Taken off the caliper, seals and piston are fine and piston moves as it should

Brake pipe is clear.

Tried to bleed at the banjo instead and nothing

Can’t bleed at the MS banjo due to the design of the bike and no access.

Any other suggestions?
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xX-Alex-Xx
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PostPosted: 22:53 - 23 Jan 2022    Post subject: Reply with quote

Vacuum pump should work... You did have the cap off the reservoir when you tried?
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Farmingstock
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PostPosted: 23:26 - 23 Jan 2022    Post subject: Reply with quote

Yeah cap off the res, it just doesn’t seem to move any fluid out of the MS res, the vac pump builds up on the pump but when I open the bleed nipple the pressure drops instantly
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Easy-X
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PostPosted: 01:13 - 24 Jan 2022    Post subject: Reply with quote

Sounds like a blockage somewhere. If you disconnect the pipe from the master and try a reverse fill it should piss out the end.

My bet is either a rebuild of the M/C required or something stupid like the bleed nipple is totally bunged up.
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jaffa90
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PostPosted: 02:28 - 24 Jan 2022    Post subject: Reply with quote

[quote="Easy-X"]Sounds like a blockage somewhere. If you disconnect the pipe from the master and try a reverse fill it should piss out the end.

My bet is either a rebuild of the M/C required or something stupid like the bleed nipple is totally bunged up.
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jeffyjeff
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PostPosted: 07:38 - 24 Jan 2022    Post subject: Re: Brakes won’t bleed Reply with quote

1. Taken off the MS seals are fine and build pressure
2. Taken off the caliper, seals and piston are fine and piston moves as it should
3. Brake pipe is clear.
4. Tried to bleed at the banjo instead and nothing
5. Can’t bleed at the MS banjo due to the design of the bike and no access.

Assuming MS indicates Master Cylinder.

If you cannot bleed at the master cylinder banjo, how do you know that the seals are fine and build pressure...resistance on the brake pedal?

When you tried to bleed at the banjo (caliper end) you should have made a big fucking mess. If you did not, the problem lies before the caliper. Everything you have written suggests a blockage between the master cylinder and caliper.

First, confirm fluid is flowing through the line to the caliper. Remove the line and direct into a cup, then pump the brake pedal a few times to draw down fluid in the master cylinder.

If fluid does not flow, I would remove the master cylinder and brake line; disassemble, clean, and inspect. Blow out the brake line with compressed air to ensure no restriction. Assemble the system and bleed.

If you confirm fluid is flowing to the caliper, your problem is in the caliper. Most likely a knackered bleed screw.
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bikenut
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PostPosted: 08:51 - 24 Jan 2022    Post subject: T Reply with quote

Sounds like the tiny hole in the master cylinder is blocked.

This tiny hole is the recuperating port that allows fluid return from the caliper when brakes are off.

Post a picture of the master cylinder which may have a remote reservoir.

Is a seal kit available ?

If the reservoir is full, the hose clear, the bleed nipple clear and open, fluid should drop out due to gravity/Syphon.

You say you tried back hleebing but the hose blew off.

You could use the caliper to back bleed but fluid needs to be in the system, else the system will not pressurise...

Picture and seals ?

Your probably gunna have to strip the master cylinder.

Do you have a guitar ?
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Nobby the Bastard
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PostPosted: 09:15 - 24 Jan 2022    Post subject: Reply with quote

The easiest way to find out if it's the master cyclinder is to undi the banjo at that end and see if you can get brake fluid in by reverse bleeding. You should be able to tell if the fuild is going in quite easily.
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kgm
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PostPosted: 09:21 - 24 Jan 2022    Post subject: Reply with quote

I too would suggest stripping the master cylinder. Although realistically you can buy a whole new master cylinder and lever setup off eBay for about 15 quid.

At this point I'd strip and clean everything, new seals all round. Cheap and easy on that bike, could be done in an hour.
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xX-Alex-Xx
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PostPosted: 09:21 - 24 Jan 2022    Post subject: Reply with quote

Farmingstock wrote:
Yeah cap off the res, it just doesn’t seem to move any fluid out of the MS res, the vac pump builds up on the pump but when I open the bleed nipple the pressure drops instantly


Indicates a blockage either in the line or (more likely) towards the master then. Have you tried pumping the lever while trying keeping a vacuum on the pump? Can you see if anything is blocking the small apertues that allow fluid to drop into the lines?
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Farmingstock
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PostPosted: 16:14 - 24 Jan 2022    Post subject: Reply with quote

thank you for the responses,

I had completely removed the brake set up to check everything but the MS isn`t accessible once fitted to the bike, meaning everything has to come off again to check anything.

I put fluid in the MS when it was off the bike, finger over the end and pumped a bit of pressure and a dribble of fluid came out it didn`t spray everywhere, just a dribble.

The seal kits and MS its self are not obtainable in the UK and definitely not for £15-20.

I have tried filling from the caliper and fluid comes out of the pipe.

Looking like an issue with the MS, can you buy generic seals and anyway of measuring them?

Cheers
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Bhud
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PostPosted: 17:37 - 24 Jan 2022    Post subject: Reply with quote

Can you remove the piston? Try pulling it out completely and pushing it in again a couple of times, in case there's a bit of dirt or something blocking the in or out fluid holes. This might be enough to push out an obstruction. Make sure you don't put in any kind of fluid except brake fluid.

If you're going to replace seals or any brake parts at all, I recommend you stick with OEM.
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Ayrton
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PostPosted: 17:46 - 24 Jan 2022    Post subject: Reply with quote

What model bike Reiju is it? You can buy whole master cylinders with the brake calliper for some of these Chinese bikes cheaper than a seal kit may even cost Laughing
https://www.ebay.co.uk/itm/173831628710?epid=5030234721&hash=item28792c27a6:g:LMYAAOSw-lVhqDZv
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Nobby the Bastard
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PostPosted: 17:54 - 24 Jan 2022    Post subject: Reply with quote

Was it working before you decided to change the fluid?

If so, you've probably dropped something into the master cylinder.

Always assuming you didn't remove the whole system just touching the fluid...
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Farmingstock
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PostPosted: 18:56 - 24 Jan 2022    Post subject: Reply with quote

It’s an RS3 2018, I’ll get a picture of the MS when I take it off but it’s not a generic one unfortunately.

The rear brake was very soft and spongy prior to removing the fluid, didn’t stop the bike.

I cleaned everything before refitting, may remove again and put in ultrasonic cleaner just to make sure it’s perfect.

Is there a test to make sure the MS is fine??
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Farmingstock
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PostPosted: 19:49 - 24 Jan 2022    Post subject: Reply with quote

Taken the MS off again! I can definitely get fluid back to the banjo at the MS by pumping back from caliper bleed nipple!
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bikenut
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PostPosted: 21:23 - 24 Jan 2022    Post subject: Thread Reply with quote

Post a picture of the res floor.

A large hole more towards the phone stone rod and a tiny hole nearer the hose end


They may be covered by a tin "roof".

You did assemble the MC correctly.

You said on initial inspection that there was no fluid in the system and the brakes didn't work, so its leaked out. Good thickness of pad material ?

Any staining on the pedal end of the MC ?

Any staining on the floor of its resting place below the MC ?

With MC assembled correctly and res filled with fluid, fluid should drip out of hose end...

Do es that happen on the bench ?
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Farmingstock
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PostPosted: 21:58 - 24 Jan 2022    Post subject: Reply with quote

There was fluid in the system I was just changing it as the rear brake didn’t work properly, didn’t stop the bike but if on a stand it would slow the rear wheel if I turned it by hand!

The MC definitely wasn’t leaking before hand and doesn’t leak now either.

Trying it on the bench it doesn’t seam to build any pressure, it will dribble fluid out when I put my finger over the end but definitely doesn’t squirt out!

The piston has some marks on it like someone has messed with it before.
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bikenut
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PostPosted: 08:52 - 25 Jan 2022    Post subject: T Reply with quote

Picture fuzzy but seals look the right way.

Still not picture of res floor.

The MC should pump fluid...

Is that tiny hole blocked ?

Shine light into res and look down bore, you should see the light ...
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Farmingstock
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PostPosted: 11:47 - 25 Jan 2022    Post subject: Reply with quote

The holes look clear
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Polarbear
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PostPosted: 14:33 - 25 Jan 2022    Post subject: Reply with quote

Surely that is a generic master cylinder made by an outside company and available from other sources? I mean, even the big Japanese M/C companies buy in their brake components.
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Farmingstock
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PostPosted: 15:00 - 25 Jan 2022    Post subject: Reply with quote

I’ve looked high and low but nothing!

After an hour of bleeding I am getting somewhere, however each time there are lots of bubbles coming through, I have left zip tied the brake on to try and release some bubbles, will see how it goes.
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Bhud
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PostPosted: 16:16 - 25 Jan 2022    Post subject: Reply with quote

Polarbear wrote:
Surely that is a generic master cylinder made by an outside company and available from other sources? I mean, even the big Japanese M/C companies buy in their brake components.


I bought a new "YBR125" master cylinder once, for a project. It was cheap. Looked exactly the same as the real thing, and it was new.
However, it really wasn't! It was absolute junk. I ended up buying a used YBR125 master cylinder to replace it. Both the assembly and the components were different. The brake light switch on the Chinese one was a tiny bit of ABS plastic secured in place by a key ring... Yeah. The actual piston was different and the hole sizes were different, and it didn't draw in enough fluid quickly enough. It had a bit of solid plastic as the cap seal. The used one (actual Yamaha) looked shabby but it was a completely different kettle of fish!


Last edited by Bhud on 16:20 - 25 Jan 2022; edited 1 time in total
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Bhud
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PostPosted: 16:19 - 25 Jan 2022    Post subject: Reply with quote

Farmingstock wrote:
there are lots of bubbles coming through


Your seals are not visible damaged from what I can see in the photo. There are scratches on the piston but I can only speculate someone got in there with a bit of guitar wire or something in an attempt to clean the holes. If you're getting bubbles you're getting somewhere and they are pumping so keep going! If the bubbles are coming up I'd just keep doing it the conventional way. I don't think zip tying it down will be enough. There is probably lots of air in it. Just keep going.
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Farmingstock
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PostPosted: 19:22 - 25 Jan 2022    Post subject: Reply with quote

Pretty much there I think, probably still some bubbles in there but the back wheel locks up now and the pedal is solid, much better than it was when I started, that is for sure
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