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Mike, Honda Technician
Category: Honda
Satisfied Customers: 39198
Experience:  Tech Expert
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My car failed its mot on the brake pipes, therefore all metal

Resolved Question:

My car failed its mot on the brake pipes, therefore all metal brake pipes were replaced with copper. Brakes were then bled, all air from system. Brake pedal was fine until car started and then faded into floor. Definitely no fluid leaks at all.

If all 4 brake flexes are clamped a full pedal is achieved, even with car running. Take any one clamp off and car pedal fades to the floor on start up.
Have replaced master cylinder and servo from breakers yard and have the same symptoms. If I pipe from the 2 outlets on the master cylinder, direct to front callipers, brakes fade on start up. If I connect to one front calliper and blank one side of master cylinder, full pedal even on start up. I have replaced master cylinder with brand new one and now brake pedal is slightly better, but I have no servo assistance. Vacum pipe is vacuuming through the servo as it should.

I have been a mechanic for years and never had this problem before. At the end of my tether with it. Does anyone know what to do next?
Submitted: 2 years ago.
Category: Honda
Expert:  Mike replied 2 years ago.
Hello and Welcome -

My name is XXXXX XXXXX Im happy to help you ..

Having read through all you have done - it would appear that the master cylinder was your issue - most likely caused by the bleeding etc - but whatever you have changed that now for new so thats good - and I assume you have re bled the brakes fully... with the new one on... If not - then you need to do that...

Too - some can be espeically difficult to bleed - if you are doing it "manually" - I suggest to use a pressure bleeder - you can get these at a reasonable price from car shops etc that work ok.. Often that is whats needed on the more modern vehicle to be sure of a good bleed.

Re the servo now though - you have no servo working..

If the vacuum is there as it should be- then you can only have a faulty servo... That wouldn't be surprising being its second hand- I would actually suggest to re fit your old one and retry as its likely ok Check the connections to it from the pedal are all ok as well.. Again - if the vacuum is there - it either (the servo) is not being actuated by the pedal properly -or, its faulty inside.

When you have sorted the servo, bleed the brakes as above - with the engine running, that should ensure it bleeds properly.. Then - however the pedal feels, take it for a drive - often it will come right / as it should be after its driven. ( Vw's etc are all like that too )

Do let me know if you need anything else at all -

Kind Rgds - MIKE.

...Meantime..............Please do click on the "OK/ Excellent ratings" for me for my time etc - as that's how Im credited for helping you - Thank you in advance for that...

You can and are most welcome to get back to me anytime you might need - clicking the OK ratings does not close you out at all..

Rgds, MIKE.

Mike, Honda Technician
Category: Honda
Satisfied Customers: 39198
Experience: Tech Expert
Mike and other Honda Specialists are ready to help you
Customer: replied 2 years ago.

Hi Mike,

many thanks for that, feel like I'm going mad with this, never had this problem before.


Re bleeding, I have used a high pressure bleeder, though I didn't have the car running at the time.


Re servo, I have put the original one back on though just about to re-check the connections to it from the pedal as you suggested.


Hopefully your advice will put me back on the right track.

Many thanks again


Expert:  Mike replied 2 years ago.
Hello again Darren -

My apologies - I have been on a break.

Thank you for your reply.

As a further thought - make sure the one way valve in the servo supply pipe is operating as it should - that can cause odd issues / non working servo / binding brakes etc... Let me know how you get on.

Best Rgds, MIKE.
Customer: replied 2 years ago.

Hi Mike, thanks for getting back to me.

I'm afraid I have not been able to pin down the original problem again.

Here's the outcome of my investigations.


Today I put a new seal in the servo and that fixed the servo problem but I'm still back to the initial problem with losing pressure.


I also pipe clamped all 4 corner flexes after bleeding air out of system. This gives full pedal even with engine started and holds pressure. If I released 1 clamp only a slight drop in pressure found, which I would think is normal but as soon as I release any of the others in addition to the first one, the pedal drops to the floor.


Have bled the system with engine running as you suggested and taken the car for a considerable drive, to no avail.


Thinking about it tonight, I have a questions you may be able to answer.

  • If i clamp front offside and rear nearside, am I right in assuming the brakes are in a diagonal dual circuit? If I pipe clamp diagonals will that prove if theres a fault in that circuit?


As the system holds pressure: engine started with all 4 flexis clamped, everything I have replaced, i.e. master cylinder and all steel brake pipes must be holding pressure and not bypassing or leaking. Do you agree with this?


Just wanted to highlight, 1 brake pipe burst during mot test. Don't know if this has anything to do with my problem.


ps next course of action, a box of swanvesta's!!


Look forward to your response.






Expert:  Mike replied 2 years ago.
Hello again Darren..

Ok -- well generally speaking yes - clamping the pipes should ID the faulty circuit...

I have known on odd occasions where when brake pipes have been replaced - the wrong unions have been used - meaning on pedal "up" - it draws air back into the system, via past the threads on the unions.

Also - are you sure the flares you have used are the correct ones - ie, Op1 / Op2.. you know - when you flare the pipes.. If not - they will draw air in - not necessarily leak fluid..

Too - you can pressurize the system - leave it pressurized - check for leaks.. bubbles in the master - and any leak in the component parts.

After that - as above, Im assuming you have ABS on this.. and I would say then, thats the problem - trapped air in the Abs pump... These generally will clear with a "garage" compressed air pump arrangement - you may have to resort to that Darren - at least to try ... before condemning the Abs pump etc....

Let me know how you get on...

Best Rgds, MIKE.

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