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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> More front brake issues
Post Info TOPIC: More front brake issues
Firestorm809


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Front brake issue.
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Help I'm losing the will to live 😫...the front brake was never any good when I bought the bike so I replaced the pads, serviced the caliper (pins and rubbers) and serviced the master cylinder. I also put fresh dot 4 fluid in. My issue is I don't seem to be generating pressure from the master cylinder. I have disconnected the hose and little oil is coming out from the reservoir. So a few questions:

1. Does anyone have a photo on how the master cylinder plunger looks, in particular the seal near the spring.

 

2. A brief description on how the system works. I notice 2 holes in the reservoir, one much smaller than the other.

 

3. Any independent tests I can perform on the master cylinder subassembly to make sure it's working correctly. 

 

Matthew

 

 



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TTRfan


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Sorry to hear of your brake problems Matthew.

All my knowledge about the TTR master cylinder went into the guide here . The page also includes tips on bleeding.

Brian



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Firestorm809


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Awww bloody hell my main seal was on back to front. It's been one of those days 🙄...cheers Brian

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Firestorm809


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More front brake issues
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My front brake problems seem to be never ending. I have serviced the master cylinder using the all balls kit. I have also serviced the front caliper. I'm still unable to bleed the system, i simply cannot get any pressure build up. After many tests it seems air is getting in via the piston in the master cylinder. Has anybody had this issue in the past? Would this be a new master cylinder piston or new master cylinder housing? 



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TTRfan


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If you loosen the banjo where the brake hose attaches to the caliper, can you squeeze fluid out of that joint?  Messy thing to do I know but you sound desperate cry



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Firestorm809


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Hi Brian

No I cannot get it to travel down the brake line under pressure. I have tested the brake line by injecting fluid down it in a syringe and it's ok. I'm just wondering if putting a vacuum pump on it may resolve it....not that I have a vaccum pump.

Matthew

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ttboof


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They either go OK or are a headache 

I used a syringe and a bit of hose and filled the system from the bleed bolt up and it worked 

Just a different way of doing it 



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mossproof


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Try using the syringe to suck at the caliper end. First remove the bleed nipple and grease the threads (copper grease works well and keeps it from seizing in future) this helps prevent air being drawn in via the loose thread. Short length of hose to the syringe and suck away!
For some reason this master cylinder is the worst I've come across for bleeding from dry.
Good luck,
Persevere.

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Firestorm809


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After hours and hours and hours of fun I tried reverse filling the system from the bleed nipple and it worked straight away. Cheers for all the help 👍

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ttboof


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Great result  

I found rebuilding the motor and gearbox easier than bleeding the front brake biggrin



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robs


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Firestorm809 wrote:

After hours and hours and hours of fun I tried reverse filling the system from the bleed nipple and it worked straight away. Cheers for all the help 👍

 This is the only way I ever bleed brakes now as it's the only method that seems to work consistently that I've tried.



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petenz


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Firestorm809 wrote:

My front brake problems seem to be never ending. I have serviced the master cylinder using the all balls kit. I have also serviced the front caliper. I'm still unable to bleed the system, i simply cannot get any pressure build up. After many tests it seems air is getting in via the piston in the master cylinder. Has anybody had this issue in the past? Would this be a new master cylinder piston or new master cylinder housing? 

Hydraulics 101...…………………….

 

 if you remove the master cylinder …

put it on the ground below the caliper..

keeping all the brake hose below the caliper

it will bleed in half a dozens pumps..

I clamp the master cylinder to a old set of bars..

" it is very hard to bleed any system with the bleed nipple

the lowest part of the system.... air rises.."

And motor bike is one of the worst.... the caliper is

directly below the master cylinder 

 

 

..

 

 

 

 



-- Edited by petenz on Thursday 30th of May 2019 07:12:31 AM

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JOHNYBOY


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ive never heard of doing that before pete but as they say your never too old to learn a new thing john

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ttboof


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Sounds good 

Got to get the air to go up might try it next time 



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ttr steve


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very good tip



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jasparach


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Good information, i was recently bleeding my front brake and couldn't get pressure in it despite bleeding it into a jar full of fluid, reverse bleeding it so in the end after bleeding it all i tied the brake lever to the handlebar all night and the following morning lo and behold the brake fairies had  sorted it overnight and is fine since!



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tom13


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Should the vent be left unscrewed overnight, or screwed on? (sorry for the translation)



-- Edited by tom13 on Thursday 6th of August 2020 12:32:09 PM

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TTRfan


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No. The idea is to let any remaining air in the caliper and brake lines to escape up into the master cylinder.



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JOHNYBOY


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thats what i do if i cannot get all the air out tie a cable tie / lace clip from the handlebars to the front brake lever tight leave over night cut cable tie in morning you will have a good front brake john

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