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Bleeding brakes again sorry


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I had this same problem when using a new MC, wouldn't bleed and required adjustment of the push rod.

Gareth

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Thank you Chris and John for trying to help me all useful tips and much appreciated. The thing is I already have a gap across the servo of .02 So if it won't bleed at that then I am in to guess work. I was thinking is there a measurement for the master cylinder push rod to the face of the cylinder so I can measure what I have a work out what I am trying to achieve? Also I can't see whats wrong with making up a gasket to fit between the cylinder and the servo. Would this not achieve the same outcome?

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Hi Richard

You need to increase the gap by shorting the rod its trial and error as Ive mentioned the manual is a guide for like for like replacements

don't go down the road of making gaskets its not good practice and could have safety implications its a pain I know but will be worth it in the end 

Chris 

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Richard

Have you got anyway to measure how far the MS concave part is below the mounting flange, then you could reduce the top of the rod in the servo, is your dimension of 0.02 imperial or metric?

Can you give us a picture of the end of the MC, to see if there is something different with it?

I think I have an old MC, I will try and measure it tomorrow if that would be any help?

John

Edited by John L
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Richard

Having looked at my old unit, I think I have the answer to your problem,  its the valve at the very front of the master cylinder, its not closing the opening to the reservoir, and so when the valve is pushed it just sends the fluid for the front brakes back into the reservoir, I suppose you didnt notice this earlier.

I had the same problem, but not on a new unit, there is a little white plastic part that holds the seal in place, this plastic part had shrunk and was not allowing the seal to seal the port back to the reservoir, luckily my old cylinder had a good part and was able to swap it around.

I would ask PP if they can send you a new white nylon part. Here is a picture the pin should push the seal, but on this one the plastic was holding the seal like a claw.

John

IMG_2301 (2).JPG

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Hi John 

Yes my measurement was imperial. I cant take a picture of the mounting end of the cylinder yet as its still connected to the car by the brake lines. I will take it of when my bag of willpower arrives. I am reluctant to start taking it apart on the assumption that it could be the plastic seal. If I had the skill I would have rebuilt the unit myself but have read on here rebuilding can have limited success. I paid Past parts to rebuild for me as experts and they assure me they test the unit on the bench before they send them out. I would like to know what the measurement from the concave push rod to the back of the cylinder should be to compare mine. Might give me an idea of how far out I am. 

I don't know if its the tipping valve NCT but as above Past parts claim they test before send back.

Thanks Chris I hear what your saying but would have thought that the master cylinder push rod would sit back in the 'right' place. Its my old cylinder after all and I would guess the same plunger?

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I did measure my old master cylinder, the concave part of the piston to the mounting flange is approx 0.006" below the mounting flange. So there will be no interference with the pushrod pin in the servo.

This should give you some idea what to expect on yours,  let us know.

John

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APPROX 0.006' !! Wow I also tried to measure mine but don't have the skill or the toys to measure that accurately  but the depth of the concave part of the piston to the front of the flange that goes into the servo was around the same as the depth of the flange so it should have been ok with the push rod being .02 below the servo. I also put some blue tack on the end of the cylinder and pushed into the push rod and they didn't touch metal to metal but I didn't tighten the bolts. In the end I turned the nut in 1/4 of a turn (easy once I blocked the brake pedal down. thanks for the tip) I have put the cylinder on and have bled the brakes no problem. So I'm hoping all is good. If not at least I know now where it all fits, symptoms if I have a problem and how it works and can re-visit. Just waiting for it to stop raining and I'll give it a road test. Thanks for all your help on here I don't think I would have got this far without your tips and motivation thank you all

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