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New Master Brake Cylinder not working - faulty ?


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Question for those who know their hydraulics..

Brake pedal to the floor on the 300 Tdi Defender.

Replaced the MBC with a new one (TRW) and could bleed the rear brake OK.

Front brakes no fuid whatsoever.

Took the MBC in the vice and get onlly fkuid from 1 outlet.

Is this a faulty MBC or is there some internal "thinghy" that blocks the front 2 outlets when notinh is connected ?

Thanks !

 

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There is nothing internally which blocks the second port.  There are two separate pistons to deliver fluid independently to the two ports however.

master-brake3.jpg

 

You can see that you need to block the Right brake line to develop enough pressure in the middle chamber to push the left piston.  I would however expect to see some fluid expelled.

I would have it apart & make sure the left piston is free to move and that the ports to the reservoir are open.   With the right hand piston & spring removed, you should be able to push the left piston alone to see if it works.

This arrangement ensures that the rear brakes are applied just before the front.  The rear brakes act like a rudder, trying to keep the vehicle in a straight line. 

Personally, I would be inclined to send it back and buy one from a more reputable source.  If it has failed before it's even fitted, I wouldn't want to rely on it when I really need it!

Si

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Thank You !

However, sourcing another one is not easy as there seems to have changed something in the supply chain...

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4 hours ago, simonr said:

There is nothing internally which blocks the second port.  There are two separate pistons to deliver fluid independently to the two ports however.

master-brake3.jpg

 

You can see that you need to block the Right brake line to develop enough pressure in the middle chamber to push the left piston.  

Not so, if there's no pressure in the right hand line, the primary piston will simply contact the rear of the secondary piston and push it forward.

That's the whole point of dual circuit brakes, if there is a pressure loss on one circuit the other will still work.

I'd guess the secondary piston is stuck forwards, try blowing back up the front outlet to free it, or just pop it apart.

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Is it a 90? I had a terrible problem with brakes it passed mot ect but they were not right. It turned out to be that pressure regulator to the rear wheels. Dont ask me how it was limiting pressure to the front even though the front line was not going to the regulator.  So I mig welded a brake fitting removed the line going to the rear and hey presto brakes fantastic. Try that if a 90 if not well I don't know. I just rewatched your video try as the other guy said block the rear. put a welded up brake fitting into the rear. I think it needs pressure resistance from the rear circuit somehow

Edited by andy _1
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