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4RT rear brake bleeding


TimDH
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Sorry to start off here with a negative thread but I am having a complete mare with the rear brake on my 4RT.

It's been a little problematic but no big issues until 2nd last time out when I did a big jump which split the res to MC pipe,fixed that and but it then refused to bleed even though we tried new MC parts.

I replaced the MC with new and it bled easily enough,took it out again and the brake started binding as I guess in my desperation to get a brake I over adjusted it.Backed it off and pushed the pads back and no brake pressure no matter what we did.

I have bled the normal way,reverse bled,used a vacum bleeder and some of the finest trials brains have given advice it just won't bleed.

I have a new MC,tried a new hydraulic pipe and the caliper is 100 per cent not leaking.Every individual part works fine but I have no brake pressure at all.

This is the most frustrating thing I've ever come across in 40 years of bike ownership and I used to race 2 stokes!

Any help much appreciated as I'm at the point of breaking it for parts.

 

Edited by TimDH
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I have had an issue like this once on my 07 4RT, from a drained system I was having an issue getting the air out even with vacuum and reverse bleeding.  I ended up doing one last good reverse bleed and then having to pull the rear peddle off the bike lift the rear of the bike up with a strap and then pump the piston with a small rod (tip of a small screw driver) to get enough volume through the system to get the air out.  Apparently there just is not 100% of the movement in the piston from the peddle and being able to fully push it in with the driver was all I needed. 

good luck. 

Edited by jonnyc21
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I wish I new why but I found that on all of my family trials bikes it has been easier to bleed the rear brakes this way.  Daughters 06 Beta 80, Wife's 08 Gas Gas 125 (was the worst of the bunch), my 07 Montesa 4RT. 

I noticed your other post about reliability, you may want to double check your master dose not have a bur in the boar cutting the seal as well.  I know of several people that had a buddy hone the bur out of the master and then have to put new seals into the Braktech masters. 

Good luck. 

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5 hours ago, lineaway said:

You need to burp the banjo bolt on both ends of the hose. Just a quick loosening and retightning will get it moving. It helps if the caliper is higher than the m/c.

We must have done that a thousand times.

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5 hours ago, jonnyc21 said:

I wish I new why but I found that on all of my family trials bikes it has been easier to bleed the rear brakes this way.  Daughters 06 Beta 80, Wife's 08 Gas Gas 125 (was the worst of the bunch), my 07 Montesa 4RT. 

I noticed your other post about reliability, you may want to double check your master dose not have a bur in the boar cutting the seal as well.  I know of several people that had a buddy hone the bur out of the master and then have to put new seals into the Braktech masters. 

Good luck. 

It's a new MC.

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1 hour ago, TimDH said:

It's a new MC.

The ones that my friend rebuilt where all brand new on new bikes... manufacturing defects happen and it might be hard to tell what lot or year the new one you have was built. good luck.

Edited by jonnyc21
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9 hours ago, jonnyc21 said:

The ones that my friend rebuilt where all brand new on new bikes... manufacturing defects happen and it might be hard to tell what lot or year the new one you have was built. good luck.

Ok thanks I'm leaving it until I come back from skiing or I may smash it with a hammer.

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I couldn't resist another go before I go away.

Thanks to those that tried to help but I still have no brake pressure despite trying the lifting of the bike method,all the parts are fine.

On the plus side I resisited the temptation to smash it with a hammer.

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Stupid question, but have you enough free play on the pedal-m/cylinder if the brake pedal is still on? Also, the reservoir cap  and rubber can seal too well not allowing fluid to be sucked through. They can be infuriating, keep at it.

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13 hours ago, TimDH said:

I couldn't resist another go before I go away.

Thanks to those that tried to help but I still have no brake pressure despite trying the lifting of the bike method,all the parts are fine.

On the plus side I resisited the temptation to smash it with a hammer.

One more FYI on my comment about the issue with the master needing to be honed.  The bur is small and cuts a very small scratch into the rubber seal that is only easy to see under a microscope or quality magnifying glass.  Even at that size it is large enough to let in just a touch of air. 

I hope its okay to cross post from another forum, if so here is the thread on the exact issue I am talking about from ADVRider. (almost forgot one was over there)
https://www.advrider.com/f/threads/braktec-master-cylinder-problems-why.1090928/

 

PS. I see the images on the 3rd page are not showing up for me any more, however they looked a lot like post 57. - https://www.advrider.com/f/threads/braktec-master-cylinder-problems-why.1090928/page-3#post-28052194

Edited by jonnyc21
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21 hours ago, jrsunt said:

Stupid question, but have you enough free play on the pedal-m/cylinder if the brake pedal is still on? Also, the reservoir cap  and rubber can seal too well not allowing fluid to be sucked through. They can be infuriating, keep at it.

The sum total of brake pressure today is a slight movement of 1 piston and that's if I use a plunger on the MC piston.

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